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Everything you need to know about space travel (almost)

We're a long way from home...

Paul Parsons

When did we first start exploring space?

The first human-made object to go into space was a German V2 missile , launched on a test flight in 1942. Although uncrewed, it reached an altitude of 189km (117 miles).

Former Nazi rocket scientists were later recruited by both America and Russia (often at gunpoint in the latter case), where they were instrumental in developing Intercontinental Ballistic Missiles (ICBMs) – rockets capable of carrying nuclear weapons from one side of the planet to the other.

It was these super-missiles that formed the basis for the space programmes of both post-war superpowers. As it happened, Russia was the first to reach Earth orbit, when it launched the uncrewed Sputnik 1 in October 1957, followed a month later by Sputnik 2, carrying the dog Laika – the first live animal in space.

The USA sent its first uncrewed satellite, Explorer 1, into orbit soon after, in January 1958. A slew of robotic spaceflights followed, from both sides of the Atlantic, before Russian cosmonaut Yuri Gagarin piloted Vostok 1 into orbit on 12 April 1961, to become the first human being in space . And from there the space race proper began, culminating in Neil Armstrong and Buzz Aldrin becoming the first people to walk on the Moon as part of NASA's Apollo programme .

Why is space travel important?

Space exploration is the future. It satisfies the human urge to explore and to travel, and in the years and decades to come it could even provide our species with new places to call home – especially relevant now, as Earth becomes increasingly crowded .

Extending our reach into space is also necessary for the advancement of science. Space telescopes like the Hubble Space Telescope and probes to the distant worlds of the Solar System are continually updating, and occasionally revolutionising, our understanding of astronomy and physics.

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But there are also some very practical reasons, such as mining asteroids for materials that are extremely rare here on Earth.

One example is the huge reserve of the chemical isotope helium-3 thought to be locked away in the soil on the surface of the Moon . This isotope is a potential fuel for future nuclear fusion reactors – power stations that tap into the same source of energy as the Sun. Unlike other fusion fuels, helium-3 gives off no hard-to-contain and deadly neutron radiation.

However, for this to happen the first challenge to overcome is how to build a base on the Moon. In 2019, China's Chang’e 4 mission marked the beginning of a new space race to conquer the Moon, signalling their intent to build a permanent lunar base , while the NASA Artemis mission plans to build a space station, called Lunar Orbital Platform-Gateway , providing a platform to ferry astronauts to the Moon's surface.

Could humans travel into interstellar space and how would we get there?

It’s entirely feasible that human explorers will visit the furthest reaches of our Solar System. The stars, however, are another matter. Interstellar space is so vast that it takes light – the fastest thing we know of in the Universe – years, centuries and millennia to traverse it. Faster-than-light travel may be possible one day, but is unlikely to become a reality in our lifetimes.

It’s not impossible that humans might one day cross this cosmic gulf, though it won’t be easy. The combustion-powered rocket engines of today certainly aren’t up to the job – they just don’t use fuel efficiently enough. Instead, interstellar spacecraft may create a rocket-like propulsion jet using electric and magnetic fields. This so-called ‘ ion drive ’ technology has already been tested aboard uncrewed Solar System probes.

Another possibility is to push spacecraft off towards the stars using the light from a high-powered laser . A consortium of scientists calling themselves Breakthrough Starshot is already planning to send a flotilla of tiny robotic probes to our nearest star, Proxima Centauri, using just this method.

Though whether human astronauts could survive such punishing acceleration, or the decades-long journey through deep space, remains to be seen.

How do we benefit from space exploration?

Pushing forward the frontiers of science is the stated goal of many space missions . But even the development of space travel technology itself can lead to unintended yet beneficial ‘spin-off’ technologies with some very down-to-earth applications.

Notable spin-offs from the US space programme, NASA, include memory foam mattresses, artificial hearts, and the lubricant spray WD-40. Doubtless, there are many more to come.

Read more about space exploration:

• The next giant leaps: The UK missions getting us to the Moon
• Move over, Mars: why we should look further afield for future human colonies
• Everything you need to know about the Voyager mission
• 6 out-of-this-world experiments recreating space on Earth

Space exploration also instils a sense of wonder, it reminds us that there are issues beyond our humdrum planet and its petty squabbles, and without doubt it helps to inspire each new generation of young scientists. It’s also an insurance policy. We’re now all too aware that global calamities can and do happen – for instance, climate change and the giant asteroid that smashed into the Earth 65 million years ago, leading to the total extinction of the dinosaurs .

The lesson for the human species is that we keep all our eggs in one basket at our peril. On the other hand, a healthy space programme, and the means to travel to other worlds, gives us an out.

Is space travel dangerous?

In short, yes – very. Reaching orbit means accelerating up to around 28,000kph (17,000mph, or 22 times the speed of sound ). If anything goes wrong at that speed, it’s seldom good news.

Then there’s the growing cloud of space junk to contend with in Earth's orbit – defunct satellites, discarded rocket stages and other detritus – all moving just as fast. A five-gram bolt hitting at orbital speed packs as much energy as a 200kg weight dropped from the top of an 18-storey building.

And getting to space is just the start of the danger. The principal hazard once there is cancer-producing radiation – the typical dose from one day in space is equivalent to what you’d receive over an entire year back on Earth, thanks to the planet’s atmosphere and protective magnetic field.

Add to that the icy cold airless vacuum , the need to bring all your own food and water, plus the effects of long-duration weightlessness on bone density, the brain and muscular condition – including that of the heart – and it soon becomes clear that venturing into space really isn’t for the faint-hearted.

When will space travel be available to everyone?

It’s already happening – that is, assuming your pockets are deep enough. The first self-funded ‘space tourist’ was US businessman Dennis Tito, who in 2001 spent a week aboard the International Space Station (ISS) for the cool sum of $20m (£15m).

Virgin Galactic has long been promising to take customers on short sub-orbital hops into space – where passengers get to experience rocket propulsion and several minutes of weightlessness, before gliding back to a runway landing on Earth, all for $250k (£190k). In late July 2020, the company unveiled the finished cabin in its SpaceShipTwo vehicle, suggesting that commercial spaceflights may begin shortly.

Meanwhile, Elon Musk’s SpaceX , which in May 2020 became the first private company to launch a human crew to Earth orbit aboard the Crew Dragon , plans to offer stays on the ISS for $35k (£27k) per night. SpaceX is now prototyping its huge Starship vehicle , which is designed to take 100 passengers from Earth to as far afield as Mars for around $20k (£15k) per head. Musk stated in January that he hoped to be operating 1,000 Starships by 2050.

10 Short Lessons in Space Travel by Paul Parsons is out now (£9.99, Michael O'Mara)

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Basics of Spaceflight: Glossary

Use your browser's " FIND " capability to locate a word right away on this page. You should also have a good English dictionary at hand. Additional resources are the "SEARCH BSF" function at the bottom of each page, and the Units of Measure section. You might also wish to consult the SEDS Basic Astronomical Terms page, or the NASA Thesaurus . Some additional glossaries that may be useful are linked here .

a, A -- Acceleration. a = Δ velocity / Δ time. Acceleration = Force / Mass

A -- Ampere, the SI base unit of electric current.

Å -- Angstrom (0.0001 micrometer, 0.1 nm).

A Ring -- The outermost of the three rings of Saturn that are easily seen in a small telescope.

AAAS -- American Association for the Advancement of Science.

AACS -- Attitude and Articulation Control Subsystem onboard a spacecraft.

AAS -- American Astronomical Society.

AC -- Alternating current.

Acceleration -- Change in velocity . Note that since velocity comprises both direction and magnitude (speed), a change in either direction or speed constitutes acceleration.

ALT -- Altitude.

ALT -- Altimetry data.

AM -- Ante meridiem (Latin: before midday), morning.

am -- Attometer (10 -18 m).

AMMOS -- Advanced Multimission Operations System.

Amor -- A class of Earth-crossing asteroid .

AO -- Announcement of Opportunity.

AOS -- Acquisition Of Signal, used in DSN operations.

Aphelion -- Apoapsis in solar orbit.

Apoapsis -- The farthest point in an orbit from the body being orbited.

Apogee -- Apoapsis in Earth orbit.

Apochron -- Apoapsis in Saturn orbit.

Apojove -- Apoapsis in Jupiter orbit.

Apollo -- A class of Earth-crossing asteroid .

Apolune -- Apoapsis in lunar orbit.

Apselene -- Apoapsis in lunar orbit.

Argument -- Angular distance.

Argument of periapsis -- The argument (angular distance) of periapsis from the ascending node.

Ascending node -- The point at which an orbit crosses a reference plane (such as a planet's equatorial plane or the ecliptic plane) going north.

Asteroids -- Small bodies composed of rock and metal in orbit about the Sun.

Aten -- A class of Earth-crossing asteroid .

Attometer -- 10 -18 meter.

Astronomical Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

au -- Astronomical Unit, based on the mean Earth-to-Sun distance, 149,597,870 km. Refer to "Units of Measure" section for complete information.

AZ -- Azimuth.

B -- Bel, a unit of ratio equal to ten decibels . Named in honor of telecommunications pioneer Alexander Graham Bell.

B Ring -- The middle of the three rings of Saturn that are easily seen in a small telescope.

Barycenter -- The common center of mass about which two or more bodies revolve.

Beacon -- Downlink from a spacecraft that immediately indicates the state of the spacecraft as being one of several possible states by virtue of the presence and/or frequency of the subcarrier. See Chapter 10.

Bel -- Unit of ratio equal to ten decibels. Named in honor of telecommunications pioneer Alexander Graham Bell.

Billion -- In the U.S., 10 9 . In other countries using SI, 10 12 .

Bi-phase -- A modulation scheme in which data symbols are represented by a shift from one phase to another. See Chapter 10.

BOT -- Beginning Of Track, used in DSN operations.

BPS -- Bits Per Second, same as Baud rate.

BSF -- Basics of Space Flight (this document).

BVR -- DSN Block Five (V) Receiver.

BWG -- Beam waveguide 34-m DSS, the DSN's newest DSS design.

c -- The speed of light, 299,792 km per second.

C-band -- A range of microwave radio frequencies in the neighborhood of 4 to 8 GHz.

C Ring -- The innermost of the three rings of Saturn that are easily seen in a small telescope.

Caltech -- The California Institute of Technology.

Carrier -- The main frequency of a radio signal generated by a transmitter prior to application of any modulation.

Cassegrain -- Reflecting scheme in antennas and telescopes having a primary and a secondary reflecting surface to "fold" the EMF back to a focus near the primary reflector.

CCD -- Charge Coupled Device, a solid-state imaging detector.

C&DH -- Command and Data Handling subsystem on board a spacecraft, similar to CDS.

CCS -- Computer Command subsystem on board a spacecraft, similar to CDS.

CCSDS -- Consultative Committee for Space Data Systems, developer of standards for spacecraft uplink and downlink, including packets.

CDR -- GCF central data recorder.

CDS -- Command and Data Subsystem onboard a spacecraft.

CDSCC -- DSN's Canberra Deep Space Communications Complex in Australia.

CDU -- Command Detector Unit onboard a spacecraft.

Centrifugal force -- The outward-tending apparent force of a body revolving around another body.

Centimeter -- 10 -2 meter.

Centripetal acceleration -- The inward acceleration of a body revolving around another body.

CGPM -- General Conference of Weights and Measures, Sevres France. The abbreviation is from the French. CGPM is the source for the multiplier names (kilo, mega, giga, etc.) listed in this document.

Chandler wobble -- A small motion in the Earth's rotation axis relative to the surface, discovered by American astronomer Seth Carlo Chandler in 1891. Its amplitude is about 0.7 arcseconds (about 15 meters on the surface) with a period of 433 days. It combines with another wobble with a period of one year, so the total polar motion varies with a period of about 7 years. The Chandler wobble is an example of free nutation for a spinning non-spherical object.

Channel -- In telemetry, one particular measurement to which changing values may be assigned. See Chapter 10.

CIT -- California Institute of Technology, Caltech.

Civil Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

Clarke orbit -- Geostationary orbit.

CMC -- Complex Monitor and Control, a subsystem at DSCCs.

CMD -- DSN Command System. Also, Command data.

CNES -- Centre National d'Études Spatiales, France.

Conjunction -- A configuration in which two celestial bodies have their least apparent separation.

Coherent -- Two-way communications mode wherein the spacecraft generates its downlink frequency based upon the frequency of the uplink it receives.

Coma -- The cloud of diffuse material surrounding the nucleus of a comet.

Comets -- Small bodies composed of ice and rock in various orbits about the Sun.

CRAF -- Comet Rendezvous / Asteroid Flyby mission, cancelled.

CRS -- Cosmic Ray Subsystem, high-energy particle instrument on Voyager.

CRT -- Cathode ray tube video display device.

DC -- Direct current.

DC -- The DSN Downlink Channel, several of which are in each DSN Downlink Tracking & Telemetry subsystem, DTT.

DCC -- The DSN Downlink Channel Controller, one of which is in each DSN Downlink Channel, DC.

DCPC -- The DSN Downlink Channel Processor Cabinet, one of which contains a DSN Downlink Channel, DC.

DEC -- Declination.

Decibel -- dB , an expression of ratio (see dB, above). One tenth of a Bel. See NIST website for further definition.

Declination -- The measure of a celestial body's apparent height above or below the celestial equator.

Density -- Mass per unit volume. For example , the density of water can be stated as 1 gram/cm 3 .

Descending node -- The point at which an orbit crosses a reference plane (such as a planet's equatorial plane or the ecliptic plane) going south.

DKF -- DSN keyword file, also known as KWF.

Doppler effect -- The effect on frequency imposed by relative motion between transmitter and receiver. See Chapter 6 .

Downlink -- Signal received from a spacecraft.

DSOT -- Data System Operations Team, part of the DSMS staff.

DSCC -- Deep Space Communications Complex, one of three DSN tracking sites at Goldstone, California; Madrid, Spain; and Canberra, Australia; spaced about equally around the Earth for continuous tracking of deep-space vehicles.

DSMS -- Deep Space Mission System, the system of computers, software, networks, and procedures that processes data from the DSN at JPL.

DSN -- Deep Space Network, NASA's worldwide spacecraft tracking facility managed and operated by JPL.

DSS -- Deep Space Station, the antenna and front-end equipment at DSCCs.

DT -- Dynamical Time. Replaces Ephemeris Time, ET, as the independent argument in dynamical theories and ephemerides. Its unit of duration is based on the orbital motions of the Earth, Moon, and planets. DT has two expressions, Terrestrial Time, TT, (or Terrestrial Dynamical Time, TDT), and Barycentric Dynamical Time, TDB. More information on these, and still more timekeeping expressions, may be found at the U.S. Naval Observatory website .

DTT -- The DSN Downlink Tracking & Telemetry subsystem.

Dyne -- A unit of force equal to the force required to accelerate a 1-g mass 1 cm per second per second. Compare with Newton.

E -- Exa, a multiplier, x10 18 from the Greek "hex" (six, the "h" is dropped). The reference to six is because this is the sixth multiplier in the series k, M, G, T, P, E. See the entry for CGPM.

Earth -- Third planet from the Sun, a terrestrial planet.

Eccentricity -- The distance between the foci of an ellipse divided by the major axis.

Ecliptic -- The plane in which Earth orbits the Sun and in which solar and lunar eclipses occur.

EDL -- (Atmospheric) Entry, Descent, and Landing.

EDR -- Experiment Data Record.

EHz -- ExaHertz (10 18 Hz)

EL -- Elevation.

Ellipse -- A closed plane curve generated in such a way that the sums of its distances from the two fixed points (the foci) is constant.

ELV -- Expendable launch vehicle.

EM -- Electromagnetic.

EMF -- Electromagnetic force (radiation).

EMR -- Electromagnetic radiation.

EOT -- End Of Track, used in DSN operations.

Equator -- An imaginary circle around a body which is everywhere equidistant from the poles, defining the boundary between the northern and southern hemispheres.

Equinox -- The equinoxes are times at which the center of the Sun is directly above the Earth's equator. The day and night would be of equal length at that time, if the Sun were a point and not a disc, and if there were no atmospheric refraction. Given the apparent disc of the Sun, and the Earth's atmospheric refraction, day and night actually become equal at a point within a few days of each equinox. The vernal equinox marks the beginning of spring in the northern hemisphere, and the autumnal equinox marks the beginning of autumn in the northern hemisphere.

ERC -- NASA's Educator Resource Centers.

ERT -- Earth-received time, UTC of an event at DSN receive-time, equal to SCET plus OWLT.

ESA -- European Space Agency.

ESP -- Extra-Solar Planet, a planet orbiting a star other than the Sun. See also Exoplanet.

ET -- Ephemeris time, a measurement of time defined by orbital motions. Equates to Mean Solar Time corrected for irregularities in Earth's motions. Obsolete, replaced by TT, Terrestrial Time.

eV -- Electron volt, a measure of the energy of subatomic particles.

Exoplanet -- Extrasolar planet. A planet orbiting a star other than the Sun.

Extrasolar planet -- A planet orbiting a star other than our Sun. Exoplanet.

FDS -- Flight Data Subsystem.

FE -- Far Encounter phase of mission operations.

Femtometer -- 10 -15 meter.

Fluorescence -- The phenomenon of emitting light upon absorbing radiation of an invisible wavelength.

fm -- Femtometer (10 -15 m)

FM -- Frequency modulation.

FTS -- DSN Frequency and Timing System. Also, frequency and timing data.

FY -- Fiscal year.

G -- Universal Constant of Gravitation . Its tiny value (G = 6.6726 x 10 -11 Nm 2 /kg 2 ) is unchanging throughout the universe.

G -- Giga, a multiplier, x10 9 , from the Latin "gigas" (giant). See the entry for CGPM.

g -- Acceleration due to a body's gravity. Constant at any given place, the value of g varies from object to object (e.g. planets), and also with the distance from the center of the object. The relationship between the two constants is: g = GM/r 2 where r is the radius of separation between the masses' centers, and M is the mass of the primary body (e.g. a planet). At Earth's surface, the value of g = 9.8 meters per second per second (9.8m/s 2 ). See also weight .

g -- Gram, a thousandth of the metric standard unit of mass (see kg ). The gram was originally based upon the weight of a cubic centimeter of water, which still approximates the current value.

Gal -- Unit of gravity field measurement corresponding to a gravitational acceleration of 1 cm/sec 2 .

Galaxy -- One of billions of systems, each composed of numerous stars, nebulae, and dust.

Galilean satellites -- The four large satellites of Jupiter so named because Galileo discovered them when he turned his telescope toward Jupiter: Io, Europa, Ganymede, and Callisto.

Gamma rays -- Electromagnetic radiation in the neighborhood of 100 femtometers wavelength.

GCF -- Ground Communications Facilities, provides data and voice communications between JPL and the three DSCCs.

GDS -- Ground Data System, encompasses DSN, GCF, DSMS, and project data processing systems.

GDSCC -- DSN's Goldstone Deep Space Communications Complex in California.

GEO -- Geosynchronous Earth Orbit.

Geostationary -- A geosynchronous equatorial circular orbit. Also called Clarke orbit.

Geosynchronous -- A direct, circular, low inclination orbit about the Earth having a period of 23 hours 56 minutes 4 seconds.

GHz -- Gigahertz (10 9 Hz).

GLL -- The Galileo spacecraft.

GMT -- Greenwich Mean Time. Obsolete. UT, Universal Time is preferred.

Gravitational waves -- Einsteinian distortions of the space-time medium predicted by general relativity theory (not yet directly detected as of March 2010). (Not to be confused with gravity waves, see below.)

Gravity assist -- Technique whereby a spacecraft takes angular momentum from a planet's solar orbit (or a satellite's orbit) to accelerate the spacecraft, or the reverse. See Chapter 4.

Gravity waves -- Certain dynamical features in a planet's atmosphere (not to be confused with gravitational waves, see above).

Great circle -- An imaginary circle on the surface of a sphere whose center is at the center of the sphere.

GSSR -- Goldstone Solar System Radar, a technique which uses very high-power X and S-band transmitters at DSS 14 to illuminate solar system objects for imaging.

GTL -- Geotail spacecraft.

GTO -- Geostationary (or geosynchronous) Transfer Orbit.

HA -- Hour Angle.

Halo orbit -- A spacecraft's pattern of controlled drift about an unstable Lagrange point (L1 or L2 for example) while in orbit about the primary body (e.g. the Sun).

HEF -- DSN's high-efficiency 34-m DSS, replaces STD DSSs.

Heliocentric -- Sun-centered.

Heliopause -- The boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the Sun's influence, perhaps 100 AU from the Sun.

Heliosphere -- The space within the boundary of the heliopause, containing the Sun and solar system.

HEMT -- High-electron-mobility transistor, a low-noise amplifier used in DSN.

HGA -- High-Gain Antenna onboard a spacecraft.

Hohmann Transfer Orbit -- Interplanetary trajectory using the least amount of propulsive energy. See Chapter 4.

Horizon -- The line marking the apparent junction of Earth and sky. For the technical definition, please follow this link to the U.S. Naval Observatory's Astronomical Applications .

h -- Hour, 60 minutes of time.

Hour Angle -- The angular distance of a celestial object measured westward along the celestial equator from the zenith crossing. In effect, HA represents the RA for a particular location and time of day.

ICRF -- International Celestial Reference Frame. The realization of the ICRS provided by the adopted positions of extragalactic objects. Link .

ICRS -- International Celestial Reference System. Conceptual basis for celestial positions, aligned with respect to extremely distant objects and utilizing the theory of general relativity. Link .

IERS -- International Earth Rotation and Reference Systems Service. Link .

IF -- Intermediate Frequency. In a radio system, a selected processing frequency between RF (Radio Frequency) and the end product (e.g. audio frequency).

Inclination -- The angular distance of the orbital plane from the plane of the planet's equator, stated in degrees.

IND -- JPL's Interplanetary Network Directorate, formerly IPN-ISD.

Inferior planet -- Planet which orbits closer to the Sun than the Earth's orbit.

Inferior conjunction -- Alignment of Earth, Sun, and an inferior planet on the same side of the Sun.

Ion -- A charged particle consisting of an atom stripped of one or more of its electrons.

IPAC -- Infrared Processing and Analysis Center at Caltech campus on Wilson Avenue in Pasadena.

IPC -- Information Processing Center, JPL's computing center on Woodbury Avenue in Pasadena.

IPN-ISD -- (Obsolete. See IND) JPL's Interplanetary Network and Information Systems Directorate, formerly TMOD.

IR -- Infrared, meaning "below red" radiation. Electromagnetic radiation in the neighborhood of 100 micrometers wavelength.

IRAS -- Infrared Astronomical Satellite.

ISM -- Interstellas medium.

ISO -- International Standards Organization.

ISOE -- Integrated Sequence of Events.

Isotropic -- Having uniform properties in all directions.

IUS -- Inertial Upper Stage.

JGR -- Journal Of Geophysical Research.

Jovian -- Jupiter-like planets, the gas giants Jupiter, Saturn, Uranus, and Neptune.

JPL -- Jet Propulsion Laboratory, operating division of the California Institute of Technology.

Jupiter -- Fifth planet from the Sun, a gas giant or Jovian planet.

K -- Kelvin, the SI base unit of thermodynamic temperature.

K-band -- A range of microwave radio frequencies in the neighborhood of 12 to 40 GHz.

kg -- Kilogram. See below.

Keyhole -- An area in the sky where an antenna cannot track a spacecraft because the required angular rates would be too high. Mechanical limitations may also contribute to keyhole size. Discussed in depth under Chapter 2 .

kHz -- kilohertz.

Kilogram (kg) -- the SI base unit of mass, based on the mass of a metal cylinder kept in France. See also g (gram).

Kilometer -- 10 3 meter.

Klystron -- A microwave travelling wave tube power amplifier used in transmitters.

km -- Kilometers.

KSC -- Kennedy Space Center, Cape Canaveral, Florida.

KWF -- Keyword file of events listing DSN station activity. Also known as DKF, DSN keyword file.

Kuiper belt -- A disk-shaped region about 30 to 100 AU from the Sun considered to be the source of the short-period comets.

LAN -- Local area network for inter-computer communications.

Large Magellanic Cloud -- LMC, the larger of two small galaxies orbiting nearby our Milky Way galaxy, which are visible from the southern hemisphere.

Laser -- Light Amplification by Stimulated Emission of Radiation. Compare with Maser.

Latitude -- Circles in parallel planes to that of the equator defining north-south measurements, also called parallels.

L-band -- A range of microwave radio frequencies in the neighborhood of 1 to 2 GHz.

LCP -- Left-hand circular polarization.

Leap Second -- A second which may be added or subtracted to adjust UTC at either, both, or neither, of two specific opportunities each year.

Leap Year -- Every fourth year, in which a 366th day is added since the Earth's revolution takes 365 days 5 hr 49 min.

LECP -- Low-Energy Charged-Particular Detector onboard a spacecraft.

LEO -- Low Equatorial Orbit.

LGA -- Low-Gain Antenna onboard a spacecraft.

Light -- Electromagnetic radiation in the neighborhood of 1 nanometer wavelength.

Light speed -- 299,792 km per second, the constant c.

Light time -- The amount of time it takes light or radio signals to travel a certain distance at light speed.

Light year -- A measure of distance, the distance light travels in one year, about 63,197 au.

LMC -- Large Magellanic Cloud, the larger of two small galaxies orbiting nearby our Milky Way galaxy, which are visible from the southern hemisphere.

LMC -- Link Monitor and Control subsystem at the SPCs within the DSN DSCCs.

LNA -- Low-noise amplifier in DSN, either a maser or a HEMT.

Local time -- Time adjusted for location around the Earth or other planets in time zones.

Longitude -- Great circles that pass through both the north and south poles, also called meridians.

LOS -- Loss Of Signal, used in DSN operations.

LOX -- Liquid oxygen.

m -- Meter (U.S. spelling; elsewhere metre), the international standard of linear measurement.

m -- milli- multiplier of one one-thousandth, e.g. 1 mW = 1/1000 of a Watt, mm = 1/1000 meter.

m, M -- Mass. The kilogram is the standard unit of mass. Mass = Acceleration / Force .

M -- Mega, a multiplier, x10 6 (million) from the Greek "megas" (great). See the entry for CGPM.

M100 -- Messier Catalog entry number 100 is a spiral galaxy in the Virgo cluster seen face-on from our solar system.

Major axis -- The maximum diameter of an ellipse.

Mars -- Fourth planet from the Sun, a terrestrial planet.

Maser -- A microwave travelling wave tube amplifier named for its process of Microwave Amplification by Stimulated Emission of Radiation. Compare with Laser. In the Deep Space Network, masers are used as low-noise amplifiers of downlink signals, and also as frequency standards.

Mass -- A fundamental property of an object comprising a numerical measure of its inertia; the amount of matter in the object. While an object's mass is constant (ignoring Relativity for this purpose), its weight will vary depending on its location. Mass can only be measured in conjunction with force and acceleration .

MC-cubed -- Mission Control and Computing Center at JPL (outdated).

MCCC -- Mission Control and Computing Center at JPL (outdated).

MCD -- DSN's maximum-likelihood convolutional decoder, the Viterbi decoder.

MCT -- Mission Control Team, JPL Section 368 mission execution real-time operations.

MDSCC -- DSN's Madrid Deep Space Communications Complex in Spain.

Mean solar time -- Time based on an average of the variations caused by Earth's non-circular orbit. The 24-hour day is based on mean solar time.

Mercury -- First planet from the Sun, a terrestrial planet.

Meridians -- Great circles that pass through both the north and south poles, also called lines of longitude.

MESUR -- The Mars Environmental Survey project at JPL, the engineering prototype of which was originally called MESUR Pathfinder, later Mars Pathfinder.

Meteor -- A meteoroid which is in the process of entering Earth's atmosphere. It is called a meteorite after landing.

Meteorite -- Rocky or metallic material which has fallen to Earth or to another planet.

Meteoroid -- Small bodies in orbit about the Sun which are candidates for falling to Earth or to another planet.

MGA -- Medium-Gain Antenna onboard a spacecraft.

MGN -- The Magellan spacecraft.

MGSO -- (Obsolete. See TMOD) JPL's Multi-mission Ground Systems Office.

MHz -- Megahertz (10 6 Hz).

Micrometer -- µm, 10 -6 meter.

Micron -- Obsolete terms for micrometer, µm (10 -6 m).

Milky Way -- The galaxy which includes the Sun and Earth.

Millimeter -- 10 -3 meter.

MIT -- Massachusetts Institute of Technology.

MLI -- Multi-layer insulation (spacecraft blanketing). See Chapter 11 .

mm -- millimeter (10 -3 m).

MO -- The Mars Observer spacecraft.

Modulation -- The process of modifying a radio frequency by shifting its phase, frequency, or amplitude to carry information.

MON -- DSN Monitor System. Also, monitor data.

Moon -- A small natural body which orbits a larger one. A natural satellite. Capitalized, the Earth's natural satellite.

Moonrise -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

Moonset -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

MOSO -- Multimission Operations Systems Office at JPL.

MR -- Mars relay.

µm -- Micrometer (10 -6 m).

Multiplexing -- A scheme for delivering many different measurements in one data stream. See Chapter 10.

N -- Newton, the SI unit of force equal to that required to accelerate a 1-kg mass 1 m per second per second (1m/sec 2 ). Compare with dyne.

N -- North.

Nadir -- The direction from a spacecraft directly down toward the center of a planet. Opposite the zenith.

NASA -- National Aeronautics and Space Administration.

Nautical Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

NE -- Near Encounter phase in flyby mission operations.

Neptune -- Eighth planet from the Sun, a gas giant or Jovian planet.

NiCad -- Nickel-cadmium rechargable battery.

NIMS -- Near-Infrared Mapping Spectrometer onboard the Galileo spacecraft.

NIST -- National Institute of Standards .

nm -- Nanometer (10 -9 m).

nm -- Nautical Mile, equal to the distance spanned by one minute of arc in latitude, 1.852 km.

NMC -- Network Monitor and Control subsystem in DSN.

NOCC -- DSN Network Operations Control Center at JPL.

Nodes -- Points where an orbit crosses a reference plane.

Non-coherent -- Communications mode wherein a spacecraft generates its downlink frequency independent of any uplink frequency.

Nucleus -- The central body of a comet.

Nutation -- A small nodding motion in a rotating body. Earth's nutation has a period of 18.6 years and an amplitude of 9.2 arc seconds.

NRZ -- Non-return to zero. Modulation scheme in which a phase deviation is held for a period of time in order to represent a data symbol. See Chapter 10.

NSP -- DSN Network Simplification Project. A project that re-engineered the DSN to consolidate seven data systems into two data systems that handle the same data types.

OB -- Observatory phase in flyby mission operations encounter period.

One-way -- Communications mode consisting only of downlink received from a spacecraft.

Oort cloud -- A large number of comets theorized to orbit the Sun in the neighborhood of 50,000 au.

OPCT -- Operations Planning and Control Team at JPL, "OPSCON." Obsolete, replaced by DSOT, Data Systems Operations Team.

Opposition -- Configuration in which one celestial body is opposite another in the sky. A planet is in opposition when it is 180 degrees away from the Sun as viewed from another planet (such as Earth). For example, Saturn is at opposition when it is directly overhead at midnight on Earth.

OPNAV -- Optical Navigation (images).

OSI -- ISO's Open Systems Interconnection protocol suite.

OSR -- Optical Solar Reflector, thermal control component onboard a spacecraft.

OSS -- Office Of Space Science, NASA. Obsolete, replaced by Science Mission Directorate (SMD).

OSSA -- Office Of Space Science and Applications, NASA (Obsolete, see OSS).

OTM -- Orbit Trim Maneuver, spacecraft propulsive maneuver.

OWLT -- One-Way Light Time, elapsed time between Earth and spacecraft or solar system body.

Packet -- A quantity of data used as the basis for multiplexing, for example in accordance with CCSDS.

PAM -- Payload Assist Module upper stage.

Parallels -- Circles in parallel planes to that of the equator defining north-south measurements, also called lines of latitude.

Pathfinder -- The Mars Environmental Survey (MESUR) engineering prototype later named Mars Pathfinder.

PDS -- Planetary Data System.

PDT -- Pacific Daylight Time.

PE -- Post Encounter phase in flyby mission operations.

Periapsis -- The point in an orbit closest to the body being orbited.

Perigee -- Periapsis in Earth orbit.

Perichron -- Periapsis in Saturn orbit.

Perihelion -- Periapsis in solar orbit.

Perijove -- Periapsis in Jupiter orbit.

Perilune -- Periapsis in lunar orbit.

Periselene -- Periapsis in lunar orbit.

Phase -- The angular distance between peaks or troughs of two waveforms of similar frequency.

Phase -- The particular appearance of a body's state of illumination, such as the full or crescent phases of the Moon.

Phase -- Any one of several predefined periods in a mission or other activity.

Photovoltaic -- Materials that convert light into electric current.

PHz -- Petahertz (10 15 Hz).

PI -- Principal Investigator, scientist in charge of an experiment.

Picometer -- 10 -12 meter.

PIO -- JPL's Public Information Office.

Plasma -- Electrically conductive fourth state of matter (other than solid, liquid, or gas), consisting of ions and electrons.

PLL -- Phase-lock-loop circuitry in telecommunications technology.

Plunge -- In describing the tracking motion of an AZ-EL or ALT-AZ mounted radio telescope, to "plunge" means to exceed 90° in elevation and then to continue tracking as elevation decreases on the other side without swiveling around in azimuth. This is not a capability of DSN antennas.

Pluto -- Ninth planet from the Sun, sometimes classified as a small terrestrial planet.

pm -- Picometer (10 -12 m).

PM -- Post meridiem (Latin: after midday), afternoon.

PN10 -- Pioneer 10 spacecraft.

PN11 -- Pioneer 11 spacecraft.

Prograde -- Orbit in which the spacecraft moves in the same direction as the planet rotates. See retrograde.

PST -- Pacific Standard Time.

PSU -- Pyrotechnic Switching Unit onboard a spacecraft.

Quasar -- Quasi-stellar object observed mainly in radio waves. Quasars are extragalactic objects believed to be the very distant centers of active galaxies.

Radian -- Unit of angular measurement equal to the angle at the center of a circle subtended by an arc equal in length to the radius. Equals about 57.296 degrees.

RAM -- Random Access Memory.

RCP -- Right-hand circular polarization.

Red dwarf -- A small star, on the order of 100 times the mass of Jupiter.

Reflection -- The deflection or bouncing of electromagnetic waves when they encounter a surface.

Refraction -- The deflection or bending of electromagnetic waves when they pass from one kind of transparent medium into another.

REM -- Receiver Equipment Monitor within the Downlink Channel (DC) of the Downlink Tracking & Telemetry subsystem (DTT).

Retrograde -- Orbit in which the spacecraft moves in the opposite direction from the planet's rotation. See prograde.

RF -- Radio Frequency.

RFI -- Radio Frequency Interference.

Right Ascension -- The angular distance of a celestial object measured in hours, minutes, and seconds along the celestial equator eastward from the vernal equinox.

Rise -- As in ascending above the horizon, for the technical definition, please follow this link to the U.S. Naval Observatory's Astronomical Applications .

RNS -- GCF reliable network service.

ROM -- Read Only Memory.

RPIF -- Regional Planetary Imaging Data Facilities.

RRP -- DSN Receiver & Ranging Processor within the Downlink Channel (DC) of the Downlink Tracking & Telemetry subsystem (DTT).

RS -- DSN Radio Science System. Also, radio science data.

RTG -- Radioisotope Thermo-Electric Generator onboard a spacecraft.

RTLT -- Round-Trip Light Time, elapsed time roughly equal to 2 x OWLT.

S -- South.

s -- Second, the SI base unit of time (see this extensive definition).

SA -- Solar Array, photovoltaic panels onboard a spacecraft.

SAF -- Spacecraft Assembly Facility, JPL Building 179.

SAR -- Synthetic Aperture Radar

Satellite -- A small body which orbits a larger one. A natural or an artificial moon. Earth-orbiting spacecraft are called satellites. While deep-space vehicles are technically satellites of the Sun or of another planet, or of the galactic center, they are generally called spacecraft instead of satellites.

Saturn -- Sixth planet from the Sun, a gas giant or Jovian planet.

S-band -- A range of microwave radio frequencies in the neighborhood of 2 to 4 GHz.

SC -- Steering Committee.

SCET -- Spacecraft Event Time, equal to ERT minus OWLT.

SCLK -- Spacecraft Clock Time, a counter onboard a spacecraft.

Sec -- Abbreviation for Second.

Second -- the SI base unit of time. See this extensive definition.

SEDR -- Supplementary Experiment Data Record.

SEF -- Spacecraft event file.

SEGS -- Sequence of Events Generation Subsystem.

Semi-major axis -- Half the distance of an ellipse's maximum diameter, the distance from the center of the ellipse to one end.

Set -- As in going below the horizon, for the technical definition, please follow this link to the U.S. Naval Observatory's Astronomical Applications .

SFOF -- Space Flight Operations Facility, Buildings 230 and 264 at JPL.

SFOS -- Space Flight Operations Schedule, product of SEGS.

Shepherd moons -- Moons which gravitationally confine ring particles.

SI -- The International System of Units (metric system). See also Units of Measure .

SI base unit -- One of seven SI units of measure from which all the other SI units are derived. See SI derived unit. See also Units of Measure .

SI derived unit -- One of many SI units of measure expressed as relationships of the SI base units. For example, the watt, W, is the SI derived unit of power. It is equal to joules per second. W = m 2 ⋅ kg ⋅ s –3 (Note: the joule, J, is the SI derived unit for energy, work, or quantity of heat.) See also Units of Measure .

Sidereal time -- Time relative to the stars other than the Sun.

SIRTF -- Space Infrared Telescope Facility.

SMC -- Small Magellanic Cloud, the smaller of two small galaxies orbiting nearby our Milky Way galaxy, which are visible from the southern hemisphere.

SMD -- Science Mission Directorate, NASA (previously Office Of Space Science, OSS).

SOE -- Sequence of Events.

Solar wind -- Flow of lightweight ions and electrons (which together comprise plasma) thrown from the Sun.

SNR -- Signal-to-Noise Ratio.

SPC -- Signal Processing Center at each DSCC.

Specific Impulse -- A measurement of a rocket's relative performance. Expressed in seconds, the number of which a rocket can produce one pound of thrust from one pound of fuel. The higher the specific impulse, the less fuel required to produce a given amount of thrust.

Spectrum -- A range of frequencies or wavelengths.

SSA -- Solid State Amplifier in a spacecraft telecommunications subsystem, the final stage of amplification for downlink.

SSI -- Solid State Imaging Subsystem, the CCD-based cameras on Galileo.

SSI -- Space Services, Inc., Houston, manufacturers of the Conestoga launch vehicle.

STD -- Standard 34-m DSS, retired from DSN service.

STS -- Space Transportation System (Space Shuttle).

Subcarrier -- Modulation applied to a carrier which is itself modulated with information-carrying variations.

Sunrise -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

Sunset -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

Sun synchronous orbit -- A spacecraft orbit that precesses, wherein the location of periapsis changes with respect to the planet's surface so as to keep the periapsis location near the same local time on the planet each orbit. See walking orbit.

Superior planet -- Planet which orbits farther from the Sun than Earth's orbit.

Superior conjunction -- Alignment between Earth and a planet on the far side of the Sun.

SWG -- Science Working Group.

TAU -- Thousand AU Mission.

TCM -- Trajectory Correction Maneuver, spacecraft propulsive maneuver.

TDM -- Time-division multiplexing.

Termination shock -- Shock at which the solar wind is thought to slow to subsonic speed, well inside the heleopause.

T -- Tera, a multiplier x10 12 , from the Greek teras (monster). See the entry for CGPM.

Terrestrial planet -- One of the four inner Earth-like planets.

Three-way -- Coherent communications mode wherein a DSS receives a downlink whose frequency is based upon the frequency of an uplink provided by another DSS.

TMOD -- (Obsolete. See IPN-ISD) JPL's Telecommunications and Mission Operations Directorate. Formerly MGSO.

THz -- Terahertz (10 12 Hz).

TLM -- DSN Telemetry data.

TLP -- DSN Telemetry Processor within the DTT Downlink Channel.

TOS -- Transfer Orbit Stage, upper stage.

Transducer -- Device for changing one kind of energy into another, typically from heat, position, or pressure into a varying electrical voltage or vice-versa, such as a microphone or speaker.

Transit -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

Transponder -- Electronic device which combines a transmitter and a receiver.

TRC -- NASA's Teacher Resource Centers. Obsolete, now called Educator Resource Centers, ERC.

TRK -- DSN Tracking System. Also, Tracking data.

TRM -- Transmission Time, UTC Earth time of uplink.

True anomaly -- The angular distance of a point in an orbit past the point of periapsis, measured in degrees.

Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.

TWNC -- Two-Way Non-Coherent mode, in which a spacecraft's downlink is not based upon a received uplink from DSN.

Two-way -- Communications mode consisting of downlink received from a spacecraft while uplink is being received at the spacecraft. See also coherent .

TWT -- Traveling Wave Tube, downlink power amplifier in a spacecraft telecommunications subsystem, the final stage of amplification for downlink (same unit as TWTA).

TWTA -- Traveling Wave Tube Amplifier, downlink power amplifier in a spacecraft telecommunications subsystem, the final stage of amplification for downlink (same unit as TWT).

TXR -- DSN's DSCC Transmitter assembly.

ULS -- Ulysses spacecraft.

Uplink -- Signal sent to a spacecraft.

UPL -- The DSN Uplink Tracking & Command subsystem.

Uranus -- Seventh planet from the Sun, a gas giant or Jovian planet.

USO -- Ultra Stable Oscillator, in a spacecraft telecommunications subsystem.

UT -- Universal Time, also called Zulu (Z) time, previously Greenwich Mean Time. UT is based on the imaginary "mean Sun," which averages out the effects on the length of the solar day caused by Earth's slightly non-circular orbit about the Sun. UT is not updated with leap seconds as is UTC.

UTC -- Coordinated Universal Time , the world-wide scientific standard of timekeeping. It is based upon carefully maintained atomic clocks and is highly stable. Its rate does not change by more than about 100 picoseconds per day. The addition or subtraction of leap seconds, as necessary, at two opportunities every year adjusts UTC for irregularities in Earth's rotation. The U.S. Naval Observatory website provides information in depth on the derivation of UTC.

UV -- Ultraviolet (meaning "above violet") radiation. Electromagnetic radiation in the neighborhood of 100 nanometers wavelength.

UWV -- DSN Microwave subsystem in DSSs which includes waveguides, waveguide switches, LNAs, polarization filters, etc.

Velocity -- A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.

Venus -- Second planet from the Sun, a terrestrial planet.

VGR1 -- Voyager 1 spacecraft.

VGR2 -- Voyager 2 spacecraft.

VLBI -- DSN Very Long Baseline Interferometry System. Also, VLBI data. Link .

W -- Watt, a measure of electrical power equal to potential in volts times current in amps.

Walking orbit -- A spacecraft orbit that precesses, wherein the location of periapsis changes with respect to the planet's surface in a useful way. See Sun-synchronous.

Wavelength -- The distance that a wave from a single oscillation of electromagnetic radiation will propagate during the time required for one oscillation.

Weight -- The gravitational force exerted on an object of a certain mass. The weight of mass m is mg Newtons, where g is the local acceleration due to a body's gravity.

WWW -- World-Wide Web.

X-band -- A range of microwave radio frequencies in the neighborhood of 8 to 12 GHz.

X-ray -- Electromagnetic radiation in the neighborhood of 100 picometer wavelength.

Z -- Zulu in phonetic alphabet, stands for UT, Universal Time.

Zenith -- The point on the celestial sphere directly above the observer. Opposite the nadir.

Discover More Topics From NASA

Asteroids, Comets & Meteors

Kuiper Belt

A-F     G-M     N-R     S-Z

Asteroid: Rocks floating around in space. Some are the size of a pick-up truck. Others are hundreds of miles across.

Atmosphere: The gases held by gravity around Earth and around other planets. "Atmosphere" can also be used to talk about gases around stars.

Atom: The basic building block of matter. It is made of protons, neutrons, and electrons. There are many different kinds of atoms. For example, the simplest atom with one proton and one electron is a hydrogen atom. An atom with six protons, six neutrons, and six electrons is a carbon atom.

Aurora australis: Bright glows and bands of light that appear in the skies at night near the South Pole. They are also called the southern lights.

Aurora borealis: Bright glows and bands of light that appear in the skies at night near the North Pole. They are also called the northern lights.

Black hole: A place in space where matter and light cannot escape if they fall in.

Comet: An icy rock that lets off gas and dust, which may form tails when it is flying close to a sun.

Constellation: A group of stars in the sky. They're often named after an animal, object, or person. The stars form certain patterns based on where you are. We have one view of stars here on Earth, but from another solar system or galaxy, the constellations would look different.

Corona: The outer atmosphere of a star.

Cosmos: The universe seen as an orderly, harmonious whole.

Crater: A large, bowl-shaped dent in the ground. They can be caused by an explosion or the impact of a meteorite.

Dwarf planet: Objects that are round and orbit the sun, just like planets do. But unlike planets, dwarf planets are not able to clear their path around the sun. That means there are other objects orbiting at roughly the same distance from the sun. A dwarf planet is much smaller than a planet (smaller even than Earth's moon), but it is not a moon. Pluto is the best known of the dwarf planets.

El Niño: A weather condition that sometimes occurs in the Pacific Ocean. It is so big that it affects weather all over the world. It starts with unusually warm water in the Pacific Ocean near the equator.

Electromagnetic Spectrum: The name for all the different kinds of light and energy in the universe. This includes radio waves , microwaves , infrared radiation , visible light , ultraviolet light , X-rays , and gamma rays .

Equator: The circle around a planet or moon that is the same distance from its north pole and its south pole.

Exoplanet: A planet that freely floats between stars or one that orbits a star outside our solar system.

Galaxy: A collection of thousands to billions of stars held together by gravity. The galaxy we live in is called the Milky Way.

Gamma rays: Part of the electromagnetic spectrum , also called gamma radiation. These waves have lots of energy. They come from big events like solar flares and exploding stars.

Gas: A loose collection of atoms moving around each other.

GPS: This stands for Global Positioning System. It’s a system that uses satellites, ground stations, and receivers to tell you exactly where you are on Earth.

Gravity: A force that pulls matter together.

Greenhouse gas: Gases in the atmosphere that trap heat from the sun. Some greenhouse gases are carbon dioxide, methane, water vapor, and nitrous oxide.

Infrared: Part of the electromagnetic spectrum that we cannot see with our eyes but can feel as heat. It is made of waves released by hot objects, such as stars. We call it infrared because these waves are just a little longer than the wavelengths of red light we can see.

Kuiper Belt: A donut-shaped ring of icy objects beyond the orbit of Neptune. Pluto is the best known of these icy worlds.

La Niña: The opposite of El Niño . La Niña happens because of unusually cold sea surface temperatures across the east-central Equatorial Pacific. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest United States.

Light year: It’s not a year, or an amount of time at all. It’s the distance light travels in one year. It’s the same as 5,878,499,810,000 miles (or 9,460,538,400,000,000 meters). When things are very far away, it’s easier to talk about their distance in light years than millions or billions or trillions of miles.

Magnetic field: The space around a magnet where the magnetic force is active. Earth has a magnetic field and its extension into space helps protect us from space weather .

Mass: The amount of matter something is made of.

Matter: The stuff that everything is made of. Atoms are a tiny bit of matter. Big planets have lots of matter. Even you are made of matter!

Meteor: The streak of light caused when a meteoroid enters a planet’s atmosphere and starts to burn from the heat of friction.

Meteorite: A meteoroid that lands on the surface of a planet.

Meteoroid: A little chunk of rock in space smaller than a pick up truck. If it were bigger, it would be an asteroid .

Microwaves: Part of the electromagnetic spectrum . These waves of energy are made by stars, the clouds of gas between stars, and supernovae. There is also something called “cosmic microwave background radiation.” It’s all over the universe, and scientists study it to learn how the universe began.

Molecule: The smallest unit of a substance that still acts like the main substance. A molecule can be a single atom or a group of atoms. Water is a substance, and one molecule of water is made of two hydrogen atoms and one oxygen atom, which we write as H2O. That molecule of water still has the same properties as a glass of water. But if you split it into hydrogen and oxygen, it’s not water any more.

Moon: A natural object that travels around a bigger natural object. Planets can have moons. Dwarf planets can have moons. Even some asteroids have moons! Astronomers usually call them satellites or natural satellites.

Nebula: A cloud of dust or gas found between stars.

Neutron star: A very dense star made mostly of neutrons. It has very powerful gravitational force nearby because the whole mass of a star is pulled into one object just a few miles across.

Oort Cloud: A spherical shell around our solar system. It may contain more than a trillion icy bodies. Long-period comets (which take more than 200 years to orbit the sun) come from the Oort Cloud.

Orbit: The curved path that a planet, satellite, or spacecraft moves as it circles around another object.

Ozone layer: A part of Earth’s atmosphere that absorbs lots of the sun’s ultraviolet radiation. It is made of a gas called ozone, which is a molecule of three oxygen atoms.

Particle: A tiny amount or small piece of something.

Planet: A large body in outer space that circles around the sun or another star.

Pulsar: An object, thought to be a rapidly rotating neutron star. It releases short pulses of radio waves and other electromagnetic radiation.

Quasar: Compact area in the center of a massive galaxy that is around a supermassive black hole. They are some of the brightest objects in the universe and can be observed across the entire electromagnetic spectrum .

Radiation: The energy or particles released from sources like radioactive materials, explosions, and chemical reactions. This includes energy waves on the electromagnetic spectrum .

Radio waves: Part of the electromagnetic spectrum . Radio waves are around us here on Earth, and they’re out in space too. These waves are low energy. We use them every time we listen to the radio. They’re used to talk to satellites, too. They are also common in outer space, since they are sent out by forming stars, pulsars, supernovae, the sun, and even colliding galaxies.

Radioactive: How we describe some atoms that are unstable. They change into different kinds of atoms and release lots of energy.

Satellite: An object that orbits another object. A moon is actually a satellite. We also say satellite to refer to spacecraft people build that orbit Earth, other planets, moons, asteroids, or other objects out in space.

Solar flare: A burst of energy and particles from the sun. It releases gases, radiation waves, and magnetic storms.

Solar Panel: A piece of material that can capture sunlight and turn it into electricity.

Solar system: A set that includes a star and all of the matter that orbits it, including planets, moons, asteroids, comets, and other objects.

Solar wind: The constant stream of particles and energy emitted by the sun.

Space weather: The conditions in space that can affect Earth, satellites, and space travel. Space weather is mostly the result of solar wind and solar storms.

Spacecraft: A vehicle used for traveling in space.

Speed of Light: Light is the fastest thing in the universe. It travels 186,282 miles (299,792,458 meters) every second.

Star: A ball of shining gas, made mostly of hydrogen and helium, held together by its own gravity. Turning hydrogen into helium creates the energy that makes stars shine.

Sun: The star in the center of our solar system.

Supermassive: How we describe objects that have a million times (or more!) mass than our sun.

Supernova: The explosion of a star that makes it as bright as a whole galaxy.

Tectonics: Big movements of Earth’s crust. Tectonics creates mountain ranges, deep sea trenches, volcanoes, and earthquakes that can cause destructive tsunami waves that can cross oceans.

Ultraviolet: Part of the electromagnetic spectrum . It’s called ultraviolet because the waves are shorter than violet light. We can’t see ultraviolet light with our eyes, but some birds and insects can. Our sun emits ultraviolet radiation, and it can give you a sunburn if you’re outside without sunblock for too long.

Universe: All of space and time, and everything in it. It’s everything ever!

Vacuum: An empty space that doesn't have any matter .

Volcano: A mountain or hill that has an opening where lava, rock fragments, or gas erupt from deep inside a planet or moon.

Visible light: The part of the electromagnetic spectrum that we can see with our eyes. It’s all the colors of the rainbow.

Wave: A way energy moves from one place to another. Sometimes waves move materials the way water ripples in a pond move the water. Other times, waves don’t move anything around when they transfer energy. For example, X-rays and other waves on the electromagnetic spectrum don’t make any ripples when they move energy from place to place. We classify waves based on how long their wavelengths are. A wavelength is the distance from peak to peak (or valley to valley) of the wave.

X-Rays: Radiation with lots of energy made by very hot gases, stars, neutron stars, and gas around black holes. X-rays have so much energy they can pass though solid materials. They are part of the electromagnetic spectrum .

Explore Some Big Questions about Earth and Space!

What is the Big Bang?

Where does the sun get its energy?

What causes the seasons?

What is a planet?

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Space Tourism: Can A Civilian Go To Space?

2021 has been a busy year for private space tourism: overall, more than 15 civilians took a trip to space during this year. In this article, you will learn more about the space tourism industry, its history, and the companies that are most likely to make you a space tourist.

What is space tourism?

Brief history of space tourism, space tourism companies, orbital and suborbital space flights, how much does it cost for a person to go to space, is space tourism worth it, can i become a space tourist, why is space tourism bad for the environment.

Space tourism is human space travel for recreational or leisure purposes . It’s divided into different types, including orbital, suborbital, and lunar space tourism.

However, there are broader definitions for space tourism. According to the Space Tourism Guide , space tourism is a commercial activity related to space that includes going to space as a tourist, watching a rocket launch, going stargazing, or traveling to a space-focused destination.

The first space tourist was Dennis Tito, an American multimillionaire, who spent nearly eight days onboard the International Space Station in April 2001. This trip cost him $20 million and made Tito the first private citizen who purchased his space ticket. Over the next eight years, six more private citizens followed Tito to the International Space Station to become space tourists.

As space tourism became a real thing, dozens of companies entered this industry hoping to capitalize on renewed public interest in space, including Blue Origin in 2000 and Virgin Galactic in 2004. In the 2000s, space tourists were limited to launches aboard Russian Soyuz aircraft and only could go to the ISS. However, everything changed when the other players started to grow up on the market. There are now a variety of destinations and companies for travels to space.

There are now six major space companies that are arranging or planning to arrange touristic flights to space:

• Virgin Galactic;
• Blue Origin;
• Axiom Space;
• Space Perspective.

While the first two are focused on suborbital flights, Axiom and Boeing are working on orbital missions. SpaceX, in its turn, is prioritizing lunar tourism in the future. For now, Elon Musk’s company has allowed its Crew Dragon spacecraft to be chartered for orbital flights, as it happened with the Inspiration4 3-day mission . Space Perspective is developing a different balloon-based system to carry customers to the stratosphere and is planning to start its commercial flights in 2024.

Orbital and suborbital flights are very different. Taking an orbital flight means staying in orbit; in other words, going around the planet continually at a very high speed to not fall back to the Earth. Such a trip takes several days, even a week or more. A suborbital flight in its turn is more like a space hop — you blast off, make a huge arc, and eventually fall back to the Earth, never making it into orbit. A flight duration, in this case, ranges from 2 to 3 hours.

Here is an example: a spaceflight takes you to an altitude of 100 km above the Earth. To enter into orbit — make an orbital flight — you would have to gain a speed of about 28,000 km per hour (17,400 mph) or more. But to reach the given altitude and fall back to the Earth — make a suborbital flight — you would have to fly at only 6,000 km per hour (3,700 mph). This flight takes less energy, less fuel; therefore, it is less expensive.

• Virgin Galactic: $250,000 for a 2-hour suborbital flight at an altitude of 80 km;
• Blue Origin: approximately $300,000 for 12 minutes suborbital flight at an altitude of 100 km;
• Axiom Space: $55 million for a 10-day orbital flight;
• Space Perspective: $125,000 for a 6-hour flight to the edge of space (32 km above the Earth).

The price depends, but remember that suborbital space flights are always cheaper.

What exactly do you expect from a journey to space? Besides the awesome impressions, here is what you can experience during such a trip:

• Weightlessness . Keep in mind that during a suborbital flight you’ll get only a couple of minutes in weightlessness, but it will be truly fascinating .
• Space sickness . The symptoms include cold sweating, malaise, loss of appetite, nausea, fatigue, and vomiting. Even experienced astronauts are not immune from it!
• G-force . 1G is the acceleration we feel due to the force of gravity; a usual g-force astronauts experience during a rocket launch is around 3gs. To understand how a g-force influences people , watch this video.

For now, the most significant barrier for space tourism is price. But air travel was also once expensive; a one-way ticket cost more than half the price of a new car . Most likely, the price for space travel will reduce overtime as well. For now, you need to be either quite wealthy or win in a competition, as did Sian Proctor, a member of Inspiration4 mission . But before spending thousands of dollars on space travel, here is one more fact you might want to consider.

Rocket launches are harmful to the environment in general. During the burning of rocket fuels, rocket engines release harmful gases and soot particles (also known as black carbon) into the upper atmosphere, resulting in ozone depletion. Think about this: in 2018 black-carbon-producing rockets emitted about the same amount of black carbon as the global aviation industry emits annually.

However, not all space companies use black carbon for fuel. Blue Origin’s New Shepard rocket has a liquid hydrogen-fuelled engine: hydrogen doesn’t emit carbon but simply turns into water vapor when burning.

The main reason why space tourism could be harmful to the environment is its potential popularity. With the rising amount of rocket launches the carbon footprint will only increase — Virgin Galactic alone aims to launch 400 of these flights annually. Meanwhile, the soot released by 1,000 space tourism flights could warm Antarctica by nearly 1°C !

Would you want to become a space tourist? Let us know your opinion on social media and share the article with your friends, if you enjoyed it! Also, the Best Mobile App Awards 2021 is going on right now, and we would very much appreciate it if you would vote for our Sky Tonight app . Simply tap "Vote for this app" in the upper part of the screen. No registration is required!

Definition of 'space travel'

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space travel

• spaceflight of manned vehicles.

Example Sentences

Bezos’s focus on space travel and climate change could have the same lasting impact, Alberg said.

SpaceX, too, seemed to solidify its standing within the space industry, graduating from the status of an upstart rocket company founded by Elon Musk to a significant NASA partner, heightening popular and business interests in commercial space travel.

Musk, fielding a series of mostly softball questions, used the session to “talk to his base” on topics ranging from space travel, colonies on Mars, crypto, AI and Covid-19 vaccines.

To illustrate his continuing presidential commitment to space travel, he’ll change the name of Mar-a-Lago to Mars-a-Lago.

It was a landmark achievement for the company that aimed to show rockets could be deployed and reused, demonstrating the viability of a new era of space travel with the ultimate goal of flying humans to Mars.

SPACE TRAVEL “A rocket will never be able to leave the Earth's atmosphere,” The New York Times wrote in 1936.

Space travel is too cheap and sol-type solar systems too numerous to justify the settlement of hostile worlds.

Space travel must still be new, even if it has thirty years under its belt.

Space travel would have gotten nowhere without durilium, Kennon reflected.

Space tourism explained: What, why and where

Space tourism is an exciting development in the travel and tourism industry. A futuristic type of tourism , the prospect of being able to spend leisure time in space is a daunting concept for many. But whilst some of us may have expected only have to be able to experience space tourism using virtual reality software, several companies are turning holidays in space into a reality.

What is space tourism?

Space tourism definitions, history of space tourism, rocket launches, space museums, space tourism holidays, virgin galactic, blue origin, is space tourism safe, the cost of space tourism holidays, space tourism: conclusion, further reading.

Space tourism is a type of tourism that involves an interest in space. Whilst most people associate space tourism solely with trips to space, the concept of space tourism is, in fact, broader than this.

Space tourism can include visiting space-focussed museums, watching rocket launches or travelling to destinations popular for stargazing, amongst other space-related activities.

Most recently, there has been a lot of commercial attention centred around the concept of travelling to space as a tourist; this is something that several companies are working to achieve in the near future, including Virgin Galactic and SpaceX.

If you Google the phrase ‘what is space tourism’ you will quickly be informed by Google, Wikipedia and a range of other sources that it is travelling to space for leisure or business purposes.

I, however, contest that space tourism is solely focussed upon the act of travelling to space. There is so much more to space tourism than this! Yes, this is an exciting prospect that has grabbed the attention of the media and the public, but hold on a minute…. what about all the other space-related activities that we can do without boarding a rocket and leaving the solar system?

The people over at The Space Tourism Guide have the right idea. They state that;

‘Space Tourism is not — and should not be — confined to space alone… While we can and should consider all of the activities from space tourism companies like Virgin Galactic, Blue Origin, Zero2Infinity, and others space tourism, we should not discredit the companies and destinations here on earth who meet the needs and desires for all of us who love to travel for space-related activities. These can vary widely, from cities and museums like Space Center Houston to hotels with space-themed rooms.’

Space tourism is so much more than taking a trip to space! In fact, I argue that space tourism should encompass all activities related to space and astrology!

To date, there is little academic research into space tourism. Yes, some people have looked into astrology and the like, but on the whole, there is a dearth of information. Most research that has been conducted has focussed on looking at potential demand and market demographics.

In light of the misleading definitions that you will find when asking your favourite search engine what is meant by the term space tourism, I have provided my own definition below.

‘Space tourism is the act of taking part in activities that involve or are related to space, either for business or leisure purposes.’

So there you have it- a definition of space tourism.

There are a total of 600 people that have been to space. The first man visited space in 1961, but it was actually long before this day that many people developed an interest in space. In fact, people have been star gazing as long as records go back. Heck, even the ancient pyramids of Egypt were built around the stars .

So, the concept of space tourism is not new.

The 1950s, 60s, 70s and 80s saw huge progress in space research. The Soviet Union and The United States were world leaders in this area; undertaking many trips to space, exploring our solar system, nearby planets and moons. Space travel became more affordable and we learnt a lot during this time.

It was only at the turn of the new millennium that commercial space tourism ,whereby a tourist could travel to space, started to become a reality. A handful of wealthy citizens from around the world embarked on their leisure outings to space between 2001-2009. Observing this demand, a number of space tourism operators began to emerge, namely Blue Origin, Virgin Galactic and Rocket Lab. Said companies have since become household names.

In recent years the commercial hype and excitement towards space tourism has died down. The public continue to eagerly await the days that they may be able to exchange their all-inclusive holiday in Benidorm for a week of zero-gravity in space, but for most, this is an unrealistic and unachievable prospect.

For now, it appears that travelling into space will be available only for the super-rich, and we do not yet know when this might be attainable. BUT the space tourism industry in all its other forms (museums, star gazing, rocket launches etc) remains to be obtainable to all.

Types of space tourism

We might not realistically be able to travel into space for our annual leave days just yet, but there are still ways that we can get involved with the space tourism industry. Here are some examples.

Stargazing is a popular space tourism pastime for many. There are many parts of the world that are renowned for their stargazing potential. These are usually remote areas, where the light pollution is reduced, enabling maximum visibility.

Some popular stargazing destinations have capitalised on the tourist market by organising stargazing tours or stargazing-focussed accommodation options, such as bubble hotels. This CNN article shows you some of the best bubble hotel spots around the world. Many people use this opportunity to visit the Northern Lights or the Southern Lights too.

Lots of these destinations are perfect for practicing your astrophotography too!

Whilst a rocket launch may not be an everyday occurrence, it is possible to spectate when they do happen. Once operated only by Governments, there are now a range of private companies that undertake rocket launches.

If you travel to a destination with the sole intention of watching a rocket launch, or if you watch a rocket launch alongside other business or leisure pursuits, you can be classified as a space tourist.

A prominent part of the space tourism industry are space museums.

There are many museums throughout the world that are focussed around the concept of space, although these are most numerous in the United States and Russia. Here are some of the most highly-rated space museums.

• Smithsonian National Air and Space Museum, Washington DC, US
• Canada Aviation and Space Museum, Ottawa, Canada
• Memorial Museum of Cosmonautics, Moscow, Russia
• Pima Air and Space Museum, Arizona , US
• Intrepid Sea, Air and Space Museum, New York City, US
• Le Bourget Air and Space Museum, Paris, France
• Kennedy Space Center, Florida , US
• Cité de l’espace, Toulouse, France

As I mentioned earlier, space tourism holidays are what many people think space tourism is all about. Whilst there are other activities that constitute space tourism, space tourism holidays have gained a lot of media attention in recent years, and rightly so. Who wouldn’t pick up the paper and read an article that tells them that they can swap their two weeks in the sun for two weeks in space?

OK, so it isn’t quite so simple. It will require some adjustment to spending time at zero gravity, you might get a little travel sick and you might not return home with quite the same tan lines, BUT space tourism holidays are set to become a reality.

There are a number of companies who have been developing their space tourism products for a number of years, although exactly when we can go on our next space tourism holiday, is yet to be determined.

Space tourism companies

There are several key players in the space tourism holiday market. See below for a brief summary of each.

Virgin Galactic is perhaps one of the best known space tourism holiday companies. It is part of the wider Virgin Group and therefore has the benefit of an already well-established brand and reputation. It is owned by Richard Branson.

The company plans to send range of tourists to space and already has an extensive waitlist for eager space travellers, including the likes of Brad Pitt, Angelina Jolie, Leonardo DiCaprio, Ashton Kutcher and Justin Bieber.

Virgin Galactic has, however, had some negative publicity in recent times, with multiple delays and the in-flight loss of its VSS Enterprise spaceplane in 2014.

Unlike Virgin Galactic, SpaceX are an experienced rocket launching company that are now extending their operations to the commercial space tourism holiday market.

SpaceX was founded by Elon Musk. Their first holiday was initially scheduled for 2018, but has since been delayed.

Blue Origin plans to offer similar space tourism holidays to that offered by Virgin Galactic. With a traditional, vertical take-off rocket, the company plans to begin operations soon, although there is not firm date set yet.

Blue Origin was founded in 2000 by Mr Bezos.

Orion Span plans to send tourists to space to stay in their ‘space hotel’. The space hotel would accommodate up to six tourists at a time and would be positioned the private commercial space station, Aurora Space Station.

The CEO of Orion Span is Frank Bunger who states that the company’s ‘goal is to make space accessible to all’. They plan to begin operations in 2021.

Better known for their aircraft that do not leave the hemisphere, Boeing have also branched out into the space tourism holiday market.

Boeing’s involvement emerged from their working arrangement with NASA, whereby they have been working on the Commercial Crew Development programme, aimed at increasing involvement from private sector companies in the production of crew vehicles to be launched into orbit.

Boeing have developed a crew capsule, called the Boeing CST-100 Starliner, providing them with the opportunity to sell seats to space tourists.

There have been some concerns over the safety of space tourism, particularly after the negative publicity surrounding the Virgin Galactic loss of aircraft in 2014.

Because it’s so early in development of the space tourism industry and the FAA can’t control how companies design and manufacture their aircraft , it’s hard to say how safe space tourism holidays will be.

There have been many critiques, however, who have suggested that there will be deaths amongst tourists who seek to holiday in space. The number of accidents that have occurred during the testing phases hasn’t done much to people’s minds at ease, either.

Space tourism holidays are for everyday folk, at least not yet anyway, because you need to have a hefty sum of money in your pocket to be able to afford the ticket.

Prices start from US$250,000 and range up to tens of millions of Dollars. Whilst each space tourism holiday company will differ slightly, prices will typically include pre-departure training and equipment. For now, space tourism trips are set to be short in duration, lasting only a few hours. The intention is, however, that trips can be extended in the future to allow for prolonged stays in space.

As you can see, the space tourism industry is a prominent part of the wider tourism industry. Whilst most attention typically goes to the exciting prospect of space tourism holidays, there are also a number of other leisure pursuits that constitute space tourism.

It is likely that we will see many developments in the space tourism industry in the coming years, as research and development continues to be undertaken by a number of commercial operators. Watch this space and maybe you will be the next person to spend your annual leave days in space!

If you want to read up on the space tourism industry a little more then I can recommend the following texts-

• The Market for Space Tourism: Early Indications by Geoffrey Crouch- An overview of the Space Tourism market and its future potential
• Endurance: A Year in Space, A Lifetime of Discovery by Scott Kelly- A diary account of NASA astronaut’s experiences in space.
• Space Tourism by Patrick Stakem- A textbook introducing the concept of space tourism.

Almost three months ago, two NASA astronauts flew to space in a Boeing spacecraft – and have been stuck at the International Space Station ever since. Today on “Post Reports,” what went wrong and what this could mean for the future of spaceflight.

NASA astronauts Sunita Williams and Barry “Butch” Wilmore were supposed to be on the International Space Station for eight days. But as the Boeing Starliner capsule they were in was approaching the space station, the spacecraft’s thrusters started to fail. Since then, Boeing and NASA have struggled to figure out what went wrong. NASA decided last week that the astronauts should stay put for eight months until they could come back in a SpaceX capsule. 

Host Martine Powers speaks with space industry reporter Chris Davenport about the plan to bring the astronauts home and what the repercussions of this mission will be on Boeing and future space travel. 

Today’s show was produced by Ted Muldoon, with help from Sabby Robinson. It was edited by Reena Flores. Ted also mixed the show. Thanks to Chris Rowland. 

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NASA Extends Boeing Starliner Astronauts’ Space Station Stay to 2025

Persistent concerns with the vehicle’s propulsion systems mean Suni Williams and Butch Wilmore will return home next year in a SpaceX vehicle.

Boeing Starliner Astronauts Will Return to Earth in SpaceX Vehicle

Nasa announced that two astronauts aboard the international space station will have their stay extended by several months and that they will return on a spacex capsule because of problems with the boeing starliner..

“NASA has decided that Butch and Suni will return with Crew 9 next February and that Starliner will return uncrewed. A test flight by nature is neither safe nor routine. And so the decision to keep Butch and Suni aboard the International Space Station and bring the Boeing Starliner home uncrewed is the result of a commitment to safety.” “I talked with Butch and Suni both yesterday and today. They support the agency’s decision fully, and they’re ready to continue this mission on board I.S.S. as members of the Expedition 71 crew. Their families are doing well. Their families understand, just like the crew members when they launch, there’s always an opportunity, there’s always a possibility that they could be up there much longer than they anticipate. So the families understand that. I’m not saying it’s not hard. It is hard. It’s difficult.”

By Kenneth Chang

Two astronauts who have spent months aboard the International Space Station will have to stay there months longer after NASA decided on Saturday that they could not return on Boeing’s troubled Starliner space vehicle. They will return instead on a SpaceX capsule next year.

That decision finally brings clarity to the saga of the two NASA astronauts, Suni Williams and Butch Wilmore, who docked at the space station as part of a test flight of the Boeing vehicle. It also adds to months of difficult problems experienced by Boeing, a dominant aerospace company that has faced embarrassing setbacks in its much larger civilian aviation and defense divisions this year.

“A test flight by nature is neither safe nor routine,” Bill Nelson, the NASA administrator, said during a news conference, “and so the decision to keep Butch and Suni aboard the International Space Station and bring the Boeing Starliner home uncrewed is a result of a commitment to safety.”

Norman Knight, NASA’s flight operations director, said he had talked to Ms. Williams and Mr. Wilmore, and that they backed the extended stay in orbit, which officials have resisted describing as a stranding .

“They support the agency’s decision fully, and they’re ready to continue this mission onboard I.S.S.,” Mr. Knight said.

The Starliner episode is another black eye for Boeing, whose reputation has been badly damaged in recent years. Boeing’s defense unit, home to its space programs, has suffered from cost overruns and lengthy delays.

NASA selected Boeing and SpaceX in 2014 to develop spacecraft to take astronauts to and from the International Space Station. Under the fixed price contract, NASA was to pay Boeing up to $4.2 billion to develop Starliner, and then launch once-a-year flights carrying crews of four to orbit.

The development of Starliner repeatedly encountered technical flaws, including faulty software, flammable tape, stuck valves and parachute systems that were not strong enough.

Mr. Nelson said he had spoken with Kelly Ortberg, the new chief executive of Boeing .

“I told him how well Boeing worked with our team to come to this decision, and he expressed to me an intention that they will continue to work the problems once Starliner is back safely,” Mr. Nelson said.

But Boeing has already written off $1.6 billion in costs for Starliner. Under a fixed-price contract, Boeing is to pay the expenses of additional work needed to meet NASA’s requirements before Starliner is certified for operational flights.

If NASA requires another crewed test flight like the current one, that would cost Boeing at least hundreds of millions of dollars more.

Mr. Nelson said he was “100 percent” certain that Boeing would not back out of the contract, but later added, “They’ve spent X, will they spend Y to get to where Boeing Starliner becomes a regular part of our crew rotation? I don’t have the answer to that, nor do I think we would have the answer now.”

Meanwhile, the 737 Max, Boeing’s popular commercial jetliner, has suffered two crises, including one this year in which a panel blew off one of the planes midflight. That episode and other troubles culminated this month with the arrival of Mr. Ortberg, a former head of Rockwell Collins, an aerospace supplier.

The members of the Starliner crew were supposed to have stayed at the I.S.S. for as few as eight days. Problems almost inevitably pop up during test flights. This test flight was the first with people aboard the Starliner spacecraft, so it was not a surprise that their stay stretched out a couple of weeks.

But even after lengthy analysis and ground testing, engineers could not say with certainty why several of Starliner’s thrusters had malfunctioned before the capsule and the astronauts docked with the space station in June.

Steve Stich, manager of NASA’s commercial crew program said engineers were concerned about how the propulsion system would perform during the return trip.

The key maneuver is an engine burn by larger thrusters that leads to the spacecraft dropping out of orbit. The smaller thrusters, including the ones that malfunctioned during docking, are used to keep the spacecraft pointed in the correct direction.

Analysis of the data showed that the firing of the larger thrusters also heated up the smaller thrusters.

“These clusters have experienced more stress, more heating,” Mr. Stich said, “and so there’s a little bit more concern for how they would perform during the deorbit burn, holding the orientation of the vehicle, and then also the maneuvers required after that.”

That lingering uncertainty spurred unease and led NASA leaders to decide they should not risk the lives of Ms. Williams and Mr. Wilmore on Starliner. Instead, they elected to rely on a different spacecraft — the Crew Dragon, built by SpaceX, a company founded by Elon Musk — for the return trip.

“The polling was unanimous amongst all the NASA folks,” said Ken Bowersox, the associate administrator for NASA’s space operations mission directorate.

Mr. Bowersox and Mr. Stich conceded that Boeing engineers and officials had disagreed about the risk. Boeing thought it had demonstrated that Starliner was safe enough for Ms. Williams and Mr. Wilmore to return home on.

“I would say that we’ve had a lot of tense discussions,” Mr. Bowersox said.

No one from Boeing took part in the news conference, but Mark Nappi, the Boeing official in charge of the Starliner program at Boeing, told his team in an email, “I know this is not the decision we had hoped for, but we stand ready to carry out the actions necessary to support NASA’s decision. The focus remains first and foremost on ensuring the safety of the crew and spacecraft.”

Starliner will undock and return to Earth in early September without anyone aboard. The next launch of a SpaceX Crew Dragon could occur Sept. 24.

The spacecraft will carry only two astronauts instead of the full crew of four that had already been assigned to a six-month mission at the space station. NASA officials said it was not ready to announce which two crew members would be bumped off that launch.

That will leave two seats for Ms. Williams and Mr. Wilmore, who will remain in orbit and become full-fledged members of the space station crew. That will extend their stay at the space station to eight months.

The four astronauts — Ms. Williams, Mr. Wilmore and the two astronauts launching on Crew Dragon in September — are to return to Earth around February.

With the extended stay in space, Ms. Williams and Mr. Wilmore will remain separated from their families and friends as the seasons change from summer to fall and then winter. Holidays and other occasions on Earth will be missed.

Part of the life of an astronaut is that the timing of a mission can change on short notice. Sometimes launches are delayed. Sometimes stays in space last longer than expected.

“The name of the game is being ready for whatever happens,” Ed Lu, a former NASA astronaut, said in an interview. “Anybody’s been around the business knows that the schedules always change. When you think you’re going to launch, that could change. When you think you’re going to land, well, that could change too.”

Dr. Lu described his own experience with sudden spaceflight schedule changes after the shuttle Columbia disintegrated during re-entry on Feb. 1, 2003. At that time, the shuttles brought up most of the supplies for the space station, and with the grounding of the remaining shuttles, it seemed that the station, still under construction, might need to be abandoned.

NASA and Russian space officials came up with a plan to keep the outpost operating with skeleton crews of two astronauts launched on Russian Soyuz rockets. But NASA astronauts then were not trained for that.

“And so I got told, on a Friday night, ‘Go this weekend to Russia, and you might be home, maybe in nine months, maybe a year,’” Dr. Lu recalled.

A year and a half of training was compressed into nine weeks for Dr. Lu.

He and Yuri Malenchenko, a Russian astronaut, launched to the space station in April 2003, spent half a year in orbit and returned to Earth. Nine months after he left, he finally got back home to Houston. He was engaged but not yet married, and did not have children then.

“This is stressful on families,” Dr. Lu said. “Obviously, it’s more stressful on families with kids.”

Mr. Wilmore is married with two daughters. Ms. Williams is also married but does not have any children. NASA officials acknowledged that toll on Saturday.

“There’s always a possibility that they could be up there much longer than they anticipate,” Mr. Knight said. “So the families understand that. I’m not saying it’s not hard. It is hard.”

Ms. Williams, Mr. Wilmore and the other astronauts will not lack food, water, air and other supplies. A cargo spacecraft arrived this month, and another is due in October.

“We’ve been able to modify and adjust our cargo mission supplies to accommodate the extra mouths we’re feeding,” said Dana Weigel, the program manager for the International Space Station at NASA.

Niraj Chokshi contributed reporting.

An earlier version of this article misstated the current title of Norman Knight. He is NASA’s flight operations director, not the chief of the flight director office.

How we handle corrections

Kenneth Chang, a science reporter at The Times, covers NASA and the solar system, and research closer to Earth. More about Kenneth Chang

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Boeing faces hard questions about Starliner and its future in space

Starliner returning to earth without its crew could damage Boeing's space ambitions

This photo provided by NASA shows Boeing's Starliner spacecraft docked to the International Space Station on July 3, 2024. The capsule launched astronauts Butch Wilmore and Suni Williams to the I.S.S. but now they'll return to Earth on a Space Crew Dragon capsule. NASA/AP hide caption

WASHINGTON — The moment NASA announced that the crew of Boeing’s Starliner will return to Earth next year on a ship built by the company’s rival, SpaceX, the questions began.

NASA will bring stranded astronauts back on SpaceX — not Boeing's Starliner

NASA administrator Bill Nelson was asked how confident he was that Boeing’s spaceship would ever fly with a crew again .

“100%,” Nelson replied without hesitation. Nelson said he had just spoken to Boeing’s CEO before the press conference in Houston on Saturday, who assured him that “they intend to move forward and fly Starliner in the future.”

Not everybody is so sure.

Starliner will return from space as soon as next week. But the two astronauts who blasted off in June for what was supposed to be eight day mission at the International Space Station will now stay for eight months because of glitches that cropped up during the test flight.

It’s another blow for Boeing in what’s been a brutal year for the aerospace giant, and observers say it could have big implications for the company’s future in space.

'We’re not stuck.' Why Boeing’s Starliner isn’t returning to Earth (yet)

“Boeing is going to need to grapple with the consequences of the failure of this mission to achieve its test objectives,” said Todd Harrison, a space industry veteran who’s now a senior fellow at the American Enterprise Institute.

Boeing has changed since the contract for Starliner was awarded a decade ago , Harrison said, becoming less focused on human spaceflight.

“It’s fairly likely Boeing will, within a few weeks or months, come to the conclusion that they just need to step back” from Starliner, he said. “This program kind of sticks out as something that doesn't fit with the rest of their business.”

NASA’s Boeing Crew Flight Test Commander Butch Wilmore (L) and Pilot Suni Williams are shown heading to the launchpad for a mission to the International Space Station on June 5, 2024. The flight was supposed to last about eight days — but will now be about eight months for the astronauts. Joe Raedle/Getty Images hide caption

That would be a momentous shift for a company with a storied history in space that stretches back decades.

Ten years ago, Boeing got the lion’s share of funding for NASA’s Commercial Crew Program — more than $4 billion, while the upstart SpaceX got only $2.6 billion. Boeing has since lost an additional $1.6 billion on Starliner.

NASA’s goal all along was to have more than one private company that could get astronauts and equipment into orbit and back. Boeing’s struggles with Starliner make that strategy look smart.

The launch of Boeing’s crewed Starliner space capsule is called off yet again

“This really proves that you do need redundancy,” said Makena Young, a fellow with the Aerospace Security Project at the Center for Strategic and International Studies. “Sometimes things go wrong and you need that second plan.”

Young thinks it’s too soon to know if Boeing will walk away from the Starliner program.

“It's not a failure just yet,” Young said. “We very well could still see a success of this system, if it's able to get back to Earth and land safely.”

Space is a relatively small piece of Boeing’s portfolio. The company’s new CEO, Kelly Ortberg , has other pressing problems, like turning around the company’s commercial airline business after major safety and quality control lapses .

The engineering challenges there are very different, but observers say there are some parallels as well.

“Almost all of Boeing's problems are cultural,” says Richard Aboulafia, an aviation industry analyst at AeroDynamic Advisory. “It's a management team that was completely disconnected from the folks who actually did the design, integration and manufacture of the company's products. That's a recipe for trouble. And you've seen it in jetliners and defense products and now, of course, in space systems.”

Boeing has not said much publicly about Starliner.

NASA Associate Administrator James Free (L-R), Associate Administrator Ken Bowersox, Commercial Crew Manager Steve Stich and International Space Station Program Manager Dana Weigel speak during a news conference to discuss plans to return two astronauts who remain stranded at the International Space Station, at Johnson Space Center in Houston, Texas, last Saturday. Mark Felix/AFP via Getty Images hide caption

“I know this is not the decision we had hoped for, but we stand ready to carry out the actions necessary to support NASA's decision,” wrote Mark Nappi, the head of Boeing’s Commercial Crew Program, in an internal email that was shared by the company.

“The focus remains first and foremost on ensuring the safety of the crew and spacecraft,” Nappi said. “I have the utmost confidence in this team to prepare Starliner for a safe and successful uncrewed return with the same level of professionalism and determination as you did the first half of the mission.”

'Cozy' relationship between Boeing and the U.S. draws scrutiny amid 737 Max 9 mess

Boeing maintained that the astronauts could have returned safely on Starliner. NASA officials decided not to take that chance. But they did try to put a good spin on NASA’s relationship with Boeing.

“I think the key word is partner,” said NASA’s Ken Bowersox during the weekend press conference. “A lot of people want to focus on the contractual relationship where we're buying something from a company. This isn't completely like that, right? We have a contract with Boeing, but it's to work together to develop this capability for our country.”

That partnership between Boeing and NASA continues for now. But the International Space Station is set to be decommissioned in 2030 . It’s possible that partnership could end with it — if not sooner.

Space Tourism: Exploring the Future of Cosmic Travel

Space tourism has long been a dream for many, and recent technological advancements have brought this ambitious aspiration closer to reality. Skyrocketing beyond mere science fiction, the emerging market of space tourism has captured the imagination of entrepreneurs and enthusiasts alike.

With the potential for commercial space travel becoming increasingly tangible, the opportunity to explore the cosmos, witnessing Earth from a breathtaking vantage point, will soon be within the reach of ordinary people.

A handful of pioneering companies have ventured into the development of space tourism infrastructure, setting the stage for a new era of exploration and adventure. The industry’s flagship enterprises range from ambitious startups to well-established corporations, all working tirelessly to establish themselves as leaders in an emerging market, fueled by dreams of zero-gravity excursions and lunar vacations.

As we stand at the dawn of a new space age, it’s essential to understand the challenges and opportunities space tourism presents. While the industry is fraught with uncertainties, the promise of making what was once a privilege reserved for astronauts accessible to the general public is driving tremendous innovation. Consequently, space tourism is poised to catalyze an unprecedented era of human achievement and exploration.

Table of Contents

Definition of space tourism.

Space tourism refers to the commercial activity in which private individuals can purchase tickets to travel to space for recreational, leisure, or experiential purposes. Unlike traditional space missions primarily focused on research and development, military operations, or telecommunications, space tourism aims to make space travel accessible to people who are not professional astronauts.

This form of tourism usually involves suborbital, orbital, or lunar trips and may include activities like weightless experiences, Earth observation, and potentially even stays at space hotels or stations.

History of Space Tourism

Space tourism has its roots in the early days of human spaceflight. Alan Shepard, the first American in space, took a brief 15-minute suborbital flight in 1961, but it wasn’t until much later that the concept of space travel for ordinary citizens began to take shape.

In 2001, American businessman Dennis Tito became the first private space tourist when he paid $20 million for a trip to the International Space Station (ISS) aboard a Russian Soyuz spacecraft. Tito’s groundbreaking voyage blazed the trail for others to follow. In the following years, a handful of private individuals, including South African entrepreneur Mark Shuttleworth and American businessman Gregory Olsen, followed in Tito’s footsteps, embarking on their space adventures.

The idea of space tourism continued to develop as private companies, such as MirCorp, began making plans for commercial space travel. MirCorp, a now-defunct company, was created to establish a commercial space station called Mir-2, derived from the Russian space station Mir that operated in low Earth orbit from 1986 to 2001.

The Ansari X-Prize, a competition offering a $10 million prize to the first non-government organization to launch a reusable crewed spacecraft twice within two weeks, played a significant role in the development of the industry. In 2004, SpaceShipOne, designed by Burt Rutan and financed by Microsoft co-founder Paul Allen, claimed the prize and put space tourism on the map.

Over the years, several high-profile space tourists embarked on their own journeys to space, including Northrop Grumman Corporation researcher Anousheh Ansari, who became the first Iranian and female space tourist in 2006. Microsoft software architect Charles Simonyi visited the ISS twice (in 2007 and 2009), while Richard Garriott, a computer game developer, travelled to space in 2008. Cirque du Soleil Founder Guy Laliberté journeyed there in 2009.

Space tourism continues to evolve today, with private companies such as SpaceX, Blue Origin, and Virgin Galactic developing reusable spacecraft to make space travel more affordable and accessible to the public. While the industry is still in its infancy, the history of space tourism demonstrates that the dream of space travel is becoming a reality for people from all walks of life.

Major Players in Space Tourism

SpaceX, founded by Elon Musk in 2002, is a leader in the space tourism industry. It focuses on reusable rocket technology, allowing more affordable and accessible space travel. SpaceX has successfully launched and landed the Falcon 9 and Falcon Heavy rockets multiple times, significantly reducing costs. One of the company’s most ambitious projects is Starship, a fully reusable spacecraft designed for long-duration missions and carrying large crews. SpaceX has plans to take private passengers on lunar trips around the Moon, with the first mission tentatively scheduled for 2023.

Blue Origin

Blue Origin, led by Amazon founder Jeff Bezos, is another crucial player in the space tourism market. Founded in 2000, the company aims to make space travel more accessible through reusable rocket technology. Its flagship vehicle, the New Shepard, is designed for suborbital flights, offering passengers a few minutes of weightlessness and views of Earth from space. Blue Origin has completed multiple test flights and plans to begin commercial operations shortly.

Virgin Galactic

Virgin Galactic, founded by Sir Richard Branson in 2004, is focused on creating a world-class space tourism experience. With its unique air-launched spacecraft, SpaceShipTwo, the company aims to offer suborbital flights for passengers, providing several minutes of weightlessness and impressive views of Earth.

Virgin Galactic has completed multiple successful test flights and plans to begin commercial operations soon. More than 600 people have already secured tickets for the first flights, with prices starting at $250,000 per seat.

Although NASA is not explicitly involved in private space tourism, the agency has worked with SpaceX and other companies to support the development of commercial space travel. For example, NASA’s Commercial Crew Program has facilitated the growth of a competitive market for crew transportation to and from low-Earth orbit, serving both government and private-sector customers.

Types of Space Tourism

Suborbital space tourism focuses on taking passengers to the edge of space, providing them with a view of Earth from above and a taste of weightlessness. In these missions, spacecraft reach altitudes between 80 to 100 kilometres before returning to Earth. Suborbital flights last a few minutes and are designed to provide a thrilling and unique experience rather than extended travel to different destinations in space. Several private companies, such as Blue Origin and Virgin Galactic, are developing spacecraft for suborbital tourism .

• Blue Origin’s New Shepard : This reusable rocket system can carry up to six passengers and reaches altitudes just above the Karman line, providing a few minutes of weightlessness.
• Virgin Galactic’s SpaceShipTwo : This air-launched spacecraft also offers passengers a brief experience of weightlessness and a view of Earth from space, with potential for future improvements and modifications.

Orbital space tourism takes passengers to low Earth orbit (LEO) aboard a spacecraft that orbits our planet. These more ambitious missions allow tourists to experience life aboard a space station, observe Earth from a unique perspective, and potentially engage in scientific research. Orbital space tourism has a higher level of complexity when compared to suborbital missions, and there have been fewer orbital tourist flights to date. The Russian space agency, Roscosmos, has previously facilitated orbital space tourism missions.

International Space Station (ISS) visits : Since 2001, a select number of tourists have travelled to the ISS with the assistance of Roscosmos. These orbital missions typically last around ten days, with tourists participating in activities such as spacewalks and observing Earth from the station.

While lunar space tourism , which would involve a journey to the Moon, is not yet available, it represents a potential future development in the industry. Private space companies like SpaceX have announced plans to eventually offer lunar space tourism missions, though specific timelines and details have yet to be confirmed.

Advantages and Disadvantages of Space Tourism

Space tourism is an exciting and evolving field that offers a range of potential benefits and challenges. Here’s a look at some of the advantages and disadvantages:

• Economic Growth : The space tourism industry could become a significant revenue generator, creating jobs and stimulating investment in related sectors like aerospace engineering, hospitality, and training services.
• Technological Advancements : Commercial investment in space tourism can spur technological innovation as companies compete to offer safer, more efficient, and more affordable space travel.
• Public Engagement : The prospect of space tourism can increase public interest and engagement in space exploration and science, potentially inspiring a new generation of scientists, engineers, and ordinary people to look to the stars.
• Global Collaboration : The space tourism industry could foster international cooperation as countries and private enterprises collaborate on regulatory frameworks, safety protocols, and best practices.
• Democratization of Space : Although still expensive, the growth of space tourism could eventually make space more accessible to people other than highly trained astronauts and the military, democratizing the experience of space travel.
• Educational Value : Direct experiences of space travel could offer immense educational value, enhancing our understanding of human physiology in space and giving people a unique perspective on Earth that could promote global unity and stewardship.

Disadvantages

• Cost : Space tourism is extremely expensive, limiting access to a tiny, wealthy fraction of the population. The prices are also resource-intensive, raising questions about sustainability.
• Safety Concerns : Space travel is inherently risky. Even with advanced technology, there is the potential for catastrophic failure, which could result in loss of life.
• Environmental Impact : Rockets used in space travel produce greenhouse gases and black carbon particles that could contribute to climate change. The mining of materials for rocket construction and fuel also has environmental implications.
• Space Debris : Increased activity in space could contribute to the growing problem of space debris, which poses risks to both manned and unmanned missions.
• Regulatory and Ethical Concerns : The space tourism industry will require robust regulation to ensure safety and address a range of ethical considerations, including the potential militarization of space and the treatment of space as a commodity.
• Resource Allocation : Investment in space tourism can be seen as diverting crucial resources from other pressing issues like poverty, healthcare, and education, especially given that the immediate benefits of space tourism are likely to be enjoyed by a select few.
• Exclusivity : Given the high costs and risks involved, space tourism could exacerbate social inequalities by allowing only the wealthy to experience something as unique and transformative as space travel.

The advantages and disadvantages present compelling arguments for and against the development of the space tourism industry. As technology advances and we learn more about the implications of frequent space travel, this balance of pros and cons will likely continue to evolve.

Notable Space Tourists

Dennis Tito was the first space tourist, making history in 2001 when he visited the International Space Station (ISS) aboard a Russian Soyuz spacecraft. The American businessman and former NASA engineer paid a reported $20 million for his trip, opening the door for future space tourists.

Mark Shuttleworth followed Tito as the second space tourist in 2002. Known as the founder of Canonical Ltd., which sponsors the popular Linux-based operating system Ubuntu, the South African entrepreneur spent eight days aboard the ISS after paying about $20 million for his flight.

Gregory Olsen became the third tourist to visit the ISS in 2005. An American entrepreneur and scientist, Olsen paid roughly $20 million for his 10-day stay aboard the ISS. His trip marked another important milestone in the history of space tourism.

Anousheh Ansari was the first female space tourist and the first Iranian in space when she visited the ISS in 2006. A successful entrepreneur and philanthropist, Ansari’s journey as a space tourist garnered global attention, and she has since remained an advocate for space exploration and education .

Charles Simonyi , a Hungarian-American computer programmer who contributed to the development of Microsoft Office, made two trips to the ISS in 2007 and 2009. He is the first and only space tourist to have made multiple visits to the space station.

Richard Garriott , the British-American computer game developer and son of NASA astronaut Owen Garriott, became the sixth space tourist in 2008. His trip, which lasted 12 days, cost him around $30 million. Garriott is also known for creating the Ultima series of computer games.

Guy Laliberté , the Canadian founder of Cirque du Soleil, travelled to the ISS in 2009. A prominent philanthropist, Laliberté used his trip to raise awareness and funds for his foundation, One Drop, which aims to provide access to clean water worldwide.

Some recent noteworthy space tourists include:

• Jared Isaacman , an American billionaire and founder of Shift4 Payments, led the Inspiration4 mission in 2021, the first all-civilian spaceflight.
• Hayley Arceneaux , a pediatric cancer survivor and physician assistant, joined Isaacman on the Inspiration4 mission and became the youngest American to travel to space at 29.
• Peggy Whitson , a retired NASA astronaut who set records for the most time spent in space by an American astronaut and as the oldest female astronaut, announced in 2021 that she would return to space as a private astronaut.

These remarkable individuals have paved the way for future space tourists as the industry continues to evolve and gain momentum.

Space Tourism Destinations

Space tourism is becoming a reality, with various destinations offering unique experiences for those who want to travel beyond Earth. The first destination to consider is the  International Space Station (ISS) , which offers unparalleled access to microgravity research and breathtaking views of our planet. A select few private citizens have already visited the ISS, paving the way for more opportunities in the near future.

Suborbital space  is another popular destination in space tourism. Companies like Virgin Galactic have successfully launched tourists to the edge of the cosmos. This type of trip provides passengers with a thrilling, albeit brief, experience of weightlessness and allows them to witness the curvature of the Earth during their ascent.

The upper atmosphere presents an ideal option for those looking for a more leisurely destination. This is where passengers can experience the weightless sensation without leaving the Earth’s atmosphere. High-altitude balloons, such as those developed by World View Enterprises, can take passengers up to the edge of the atmosphere, allowing them to experience weightlessness without venturing into outer space.

Finally, one of the most ambitious and anticipated space destinations is the concept of a  space hotel . A space hotel would serve as a luxury accommodation orbiting the Earth, providing guests an unparalleled experience of living in space. Several companies are working on realizing this dream, such as the Orbital Assembly Corporation, which has plans for Voyager Station, a space hotel designed to offer its guests scientific and leisure opportunities.

In conclusion, space tourism is expanding rapidly, offering various destinations and experiences for those eager to explore the cosmos. As technology advances and commercial opportunities grow, there will likely be even more opportunities for adventurous tourists to choose from in the near future.

Space Travel Essentials

Several spacecraft are in development or operation for space tourism, such as SpaceX’s Crew Dragon and Starship, Blue Origin’s New Shepard, Virgin Galactic’s SpaceShipTwo (VSS Unity) , and Russia’s Soyuz from Roscosmos. The Crew Dragon and Starship aim to revolutionize space travel by reducing costs and increasing safety. The New Shepard is a reusable suborbital rocket designed for short trips to space, while the VSS Unity operates as a spaceplane targeting suborbital trips as well.

Most of these spacecraft are designed to transport passengers to the International Space Station (ISS) or a short stay in the Low Earth Orbit (LEO). For example, the Crew Dragon spacecraft has already transported astronauts to the ISS. The capsules and spaceplanes typically feature pressurized cabins, comfortable seating, and large windows to allow passengers to enjoy the breathtaking view of Earth below.

Training and Preparation

Space tourists will need to undergo astronaut training before embarking on their journeys to space. The Federal Aviation Administration (FAA) sets guidelines to ensure space tourist safety. The intensity and duration of training depend on the type of mission and the spacecraft being used. For example, those travelling to the ISS may require more rigorous training than those embarking on suborbital flights.

Training typically includes the following:

• Physical fitness training: To prepare the body for the rigours of space travel and adapt to microgravity environments.
• Environmental training: Familiarization with the spacecraft and its systems, including the pressurized capsule, emergency procedures, and life support systems.
• Simulation and mock-up training: To practice launch, docking, and landing procedures in a safe and controlled environment.

In summary, the essentials of space tourism include selecting an appropriate spacecraft that suits one’s travel goals and undergoing the necessary training and preparation. The future of space tourism shows promise, with advancements being made in reusable rockets, spaceplanes, and astronaut training facilities.

Experiencing Space

Weightlessness and zero-gravity.

Tourists venturing into space will experience a thrilling phenomenon known as weightlessness, also referred to as zero gravity or microgravity. This sensation occurs when the spacecraft reaches an altitude of approximately 100 km, known as the Kármán Line, and begins to enter a free-fall state. As they float through the cabin, passengers will find no discernable up or down, where normal gravity conditions do not apply.

This weightless environment permits tourists to perform actions that would be difficult or impossible on Earth. Some examples include:

• Effortlessly floating through the cabin
• Tossing objects to each other over large distances
• Spinning rapidly in midair

However, weightlessness also presents challenges as the body must adapt to this new environment. It is essential to note that some individuals may experience discomfort or motion sickness when first exposed to microgravity.

Views From Space

One of the most captivating aspects of space tourism is the breathtaking views. Tourists will be gifted with unparalleled sights as the spacecraft ascends beyond the Kármán Line at an altitude of 100 km.

Here are some highlights tourists can expect:

• Earth’s curvature : The vast, curved horizon showcases the planet’s spherical nature.
• Thin atmosphere : A thin blue layer envelops Earth, showcasing the fragility of our atmosphere.
• Landmarks : Iconic geographic features such as coastlines, mountain ranges, and sprawling deserts can be observed from space.
• Night sky : Astronauts have often marvelled at the beauty of the “dark sky”, with more stars visible than ever before due to the absence of atmospheric distortion and light pollution.

These awe-inspiring vistas often evoke a profound connection to our home planet. Space tourism offers adventurous travellers a unique opportunity to experience these phenomena firsthand while gaining a newfound appreciation of Earth’s beauty and fragility.

The Future of Space Tourism

Space tourism is rapidly becoming a reality, with several private companies leading the industry in developing innovative technologies and offering unique experiences for private astronauts. Companies such as Virgin Orbit, Axiom Space, and SpaceX have made significant strides in commercial space travel, laying the foundation for a thriving space tourism industry.

The Inspiration4 mission, a milestone for private space travel, demonstrated the possibilities of what private astronaut missions might look like in the future. With a crew of ordinary civilians, the mission opened doors for both orbital and suborbital tourism. Companies like Virgin Galactic continue to work on suborbital flights, which provide a shorter but exhilarating experience just beyond the edge of space.

Private companies like Axiom Space are also venturing into orbital tourism with initiatives such as Axiom Mission 1. This bold venture aims to send private astronauts to the International Space Station, paving the way for other similar missions. Furthermore, Axiom is developing a space hotel and a private space station for tourists. These ambitious projects can potentially revolutionize human spaceflight and establish a new era of space travel.

As the space tourism industry evolves, addressing concerns surrounding space travel’s environmental impact becomes essential; with climate change increasingly pressing, commercial space travel must prioritize sustainability. Solar power is a promising solution, providing clean energy and reducing the carbon footprint of space tourism. Private companies will need to focus on developing innovative technology to harness solar power efficiently.

As infrastructure develops, spaceports like Spaceport America and Kennedy Space Center will play a crucial role in supporting the space tourism industry. They will provide launch and landing facilities, training, and support for commercial spaceflight, enabling routine space tourism to become achievable. This, in turn, will allow the industry to expand and offer more accessibility to private astronauts.

A variety of space tourism companies are shaping this new frontier. With their efforts, it’s evident that a new age of human spaceflight is on the horizon, and the future of space tourism appears to be a limitless expanse full of possibilities.

Space Tourism Regulations and Challenges

As space tourism gains momentum, it is essential to understand the regulations and challenges surrounding this emerging industry.

The Federal Aviation Administration (FAA) plays a crucial role in regulating space tourism. It is responsible for issuing licenses and permits to private companies for launching and re-entering spaceships. The FAA ensures that every space tourism company adheres to strict safety guidelines and fulfils the necessary requirements before taking tourists on space expeditions.

One major challenge space tourism companies face is managing the expectations and risks associated with space travel. To address this issue, the concept of informed consent has been introduced. Informed consent signifies that passengers must fully comprehend the risks they will be exposed to while travelling in space. Moreover, they must voluntarily agree to undertake these risks and waive their rights to sue the company in case of accidents or mishaps.

The Kármán line, set at 100 kilometres (62 miles) above Earth’s surface, is often considered the boundary between Earth’s atmosphere and outer space. While the FAA regulates activities below this line, there is a lack of clear, international regulations for space tourism beyond the Kármán line. Developing consensus on the regulations and standards for space tourism will require cooperation from various international space agencies, such as Roscosmos, the Russian space agency.

In summary, the regulation and challenges of space tourism include managing safety protocols, informed consent, and international cooperation on space tourism standards. As the industry grows, understanding the complexities of regulations and addressing the challenges presented will be key to ensuring that space tourism becomes a safe and accessible reality for more and more people.

Impact of Space Tourism on the Economy

Space tourism’s advent can potentially create a significant economic impact. As billionaires like Jeff Bezos and Richard Branson have made headlines with their ventures in this emerging industry, we can observe growing interest among consumers. This section will explore the impact of space tourism on the economy, focusing on the involvement of billionaires, auction-based ticket sales, and the development of spaceports.

Space tourism companies, such as Blue Origin and Virgin Galactic, pioneered an industry once considered a distant dream. As a result of their ambitious investments, the space economy has witnessed rapid advancements. Tickets for space flights are auctioned, ranging from $200,000 to $300,000 per passenger. These high financial barriers ensure that only the wealthiest will initially be able to participate, though the cost is expected to drop as the industry matures.

Despite the considerable fees, there is significant demand for the unique experience that only space travel can offer. The wealth amassed by participants in the space tourism sector aids in funding research and technology development, contributing to economic growth. As the industry continues to expand, additional job opportunities may arise in sectors such as engineering, manufacturing, and hospitality.

Spaceport America is an example of a dedicated space travel hub that has the potential to invigorate local communities. This facility is located in New Mexico and serves as a launchpad and operations centre for commercial space travel. As space tourism becomes more prominent, regional economies benefit from increased tourism, job creation, and infrastructure investments associated with these spaceports.

Space tourism will undoubtedly impact the economy on multiple levels, from the participation of billionaire investors to the development of innovative spaceports. This new frontier has the potential to create jobs and drive technological advancements while offering a unique travel experience . As the sector grows, we can expect further developments to reshape how we traverse our galaxy.

Interstellar space: What is it and where does it begin?

Explore the interstellar medium here, with our ultimate guide.

How far away is interstellar space?

Have we traveled to interstellar space, what is interstellar space made of, what temperature is interstellar space, investigating interstellar space, interstellar travel, additional resources.

Interstellar space is the area between the stars, but it is far from empty. It contains vast quantities of neutrinos , charged particles, atoms, molecules, dark matter and photons ranging from the highest-energy radiation to the sluggish light of the cosmic microwave background (CMB) albeit rather sparsely spread out.

According to the National Radio Astronomy Observatory (NRAO), the average distance between stars in the Milky Way galaxy is about 5 light-years , although they are more bunched up near the center of the galaxy than in the outskirts where the sun and Earth are located. 

This means that there is a lot of space between the stars . We collectively call everything that is in this space the "interstellar medium", or ISM for short.

The composition of the ISM is broken down by the scientists at the Infrared Processing and Analysis Center (IPAC) at Caltech: the ISM is mostly composed of atoms of hydrogen (~90%) and helium (~8%), which are the two most common atoms in the universe having been created in the Big Bang , but there are also other trace elements and molecules contributing no more than 2% of the ISM. These elements, heavier than hydrogen and helium, have all originated in the deaths of stars and have been blown into space. The more generations of stars there are, the more enriched in chemical elements the ISM becomes over time. 

The boundary to interstellar space is far away, but perhaps not as far as you might think. In fact, part of our solar system is in interstellar space. 

How can this be? The definition of this interstellar space boundary is the region where the sun 's magnetic bubble weakens and comes to an end. This magnetic bubble — known as the heliosphere — is filled with plasma (ionized gas). The heliosphere is blown by the solar wind that drags magnetic field lines out from the sun.

The plasma in the ISM imparts an inward pressure on the edge of the heliosphere with its own magnetic fields and charged particles, leading to a complex and variable structure at the boundary. The solar wind starts to weaken from between 370–430 miles per hour (600–700 kilometers per hour) as it begins to come up against interstellar space and slows to about 62 mph (100 km/h ). The point at which this occurs is called the Termination Shock. The region in the heliosphere beyond the Termination Shock where the solar wind continues to slow is called the heliosheath, and then the outer boundary of the heliosphere is called the heliopause. It's at the heliopause where the solar wind stops and gives way to interstellar space, approximately 11 billion miles (18 billion km) from the sun. 

Only two active spacecraft have ever crossed the heliopause and entered interstellar space. These are NASA's Voyager 1 and 2 missions. Launched in 1977 they visited the outer planets before continuing on deeper into space. In 2005 JPL's Ed Stone, who was Voyager's project scientist before his retirement in 2022, announced that Voyager 1 had crossed the termination shock at a distance of 94 astronomical units (8.7 billion miles/14 billion km) from the sun.

NASA announced that Voyager 2 had followed suit in August 2007 at a distance of about 83 astronomical units (7.7 billion miles/12.4 billion km). Voyager 1 and Voyager 2 are headed in different directions, and the fact that they crossed the termination shock into the heliosheath at different distances from the sun suggests that the heliosphere is not symmetrical around the solar system, but is squashed. This shape is created by the balance of the strength of the solar wind outwards, and the pressure of the ISM on the heliosphere, particularly in the direction of the sun's motion through space.

Then, NASA announced that on August 25, 2012 Voyager 1 crossed the heliopause and became the first spacecraft to leave the sun's influence and enter interstellar space. It did so at a distance of 121 astronomical units (11 billion miles/18 billion km) from the sun, which is in the 'Scattered Disk' of comets near the edge of our solar system. NASA also revealed that Voyager 2 crossed the heliopause and entered interstellar space on November 5, 2018, at a distance of 121 astronomical units (11.3 billion miles/18.3 billion km). 

But how do you know when you're in interstellar space? The evidence that both spacecraft had crossed the boundary came in the form of changes to the plasma environment around them, in particular measuring a drop in the number of solar wind particles and an increase in the number of galactic cosmic rays from outside the heliosphere.

There is structure to the ISM, even around the solar system. 

The Solar System is currently passing through what astronomers call the Local Interstellar Cloud, which is a wispy cloud of neutral hydrogen gas about 30 to 40 light-years across described in greater detail by Jonathan Slavin of the Harvard–Smithsonian Center for Astrophysics . There are other clouds nearby too, and we and all these clouds exist in the "Local Bubble", which is hundreds of light-years across and blown relatively clear of gas and dust by ancient supernovae explosions from 14 million years ago, according to research led by Harvard's Catherine Zucker. Voyager 2's measurements of the magnetic field in the Local Interstellar Cloud show it to be stronger than expected, but still incredibly weak — millions of times weaker than a fridge magnet — and that it experiences some turbulence, resulting in the magnetic field orientation being tilted by 30 degrees to the plane of the galaxy.

The magnetic field of these interstellar clouds is part of the overall galactic magnetic field; every galaxy has its own intrinsic magnetic field, the origins of which are not well understood.

It's tempting to think of the Local Interstellar Cloud as being like a fog, but it is very diffuse. According to Professor Barbara Ryden of Ohio State University , the ISM's density can get as low as 0.1 atoms per cubic centimeter (although in the bigger nebulae , the density can reach 10,000 atoms per cubic centimeter). Compare this to the density of air on Earth, which is 27 million trillion (10^19) molecules per cubic centimeter. 

Almost all the medium in interstellar space — about 99% — is composed of gas, with just 1% being in the form of dust and ice particles. Even though the dust component is minor, it can have a dramatic effect that astronomers call "reddening", or at its most severe, "dust extinction". 

Dust partially absorbs visible wavelengths of light. So when light from a distant object has to pass through the dusty spiral arms of our galaxy, or through the dust in interstellar space, it becomes dimmer and redder, as described by astronomers at the Swinburne University of Technology. If there's enough dust it can block an object's visible light completely. 

While dust is problematic for visible light observations, infrared light can pass straight through it, which is why astronomers use the likes of the James Webb Space Telescope (JWST) to peer inside nebulas or see faraway galaxies.

Temperatures in the ISM can vary, depending on the local environment. 

There's hot gas present everywhere with temperatures of millions of degrees, but because this gas is so sparse, it would not feel that hot if you were inside it. Hydrogen ionized by the ultraviolet light of nearby hot stars radiates at temperatures of tens of thousands of degrees. At the other end of the scale, clumps of molecular hydrogen gas can barely get above 10 degrees above absolute zero . 

There's more than one way to study interstellar space, but Earth-based observations are difficult to achieve.

The heliosphere's magnetic field helps to protect our solar system from interstellar radiation that barrels towards us in the form of charged particles called "galactic cosmic-rays". However, because the strength of the solar wind, and hence the shape and strength of the heliosphere, waxes and wanes with the sun's 11-year cycle of activity, sometimes this galactic cosmic radiation can infiltrate the solar system. 

Fortunately, Earth is defended by both its own magnetic field and atmosphere, which deflect and block the vast majority of this incoming interstellar radiation. However, this effective planetary defense makes observing galactic cosmic radiation on a consistent basis from Earth unfeasible.

As well as sending spacecraft like the Voyagers into interstellar space, scientists can observe what is happening at the heliopause using spacecraft a little closer to home. This is exactly what NASA's Earth-orbiting Interstellar Boundary Explorer (IBEX) mission does.

IBEX detects so-called "energetic neutral atoms" (ENAs), which the IBEX website at the Southwest Research Institute describes as forming where the charged particles in the solar wind meet neutral, or stable atoms from interstellar space near the heliopause. Enough ENAs flood back towards the inner solar system that IBEX is able to detect up to several dozen per hour, allowing astronomers to study the interaction between the heliosphere and interstellar space based on where the flow of ENAs is strongest and weakest, which corresponds to activity at the heliopause. 

One major discovery has been that of a mysterious ribbon of particles that runs across the sky, in which ENA emissions are two to three times higher than elsewhere. IBEX scientist David McComas of Princeton University described the ribbon in a NASA statement as being "totally unexpected and not anticipated by any theories before we flew the mission." The ribbon remains unexplained.

Despite the vast distances between the stars, future interstellar spacecraft could possibly use the ISM to fuel their colossal voyages.

Traveling fast enough to reach the nearest stars in a few decades would take a vast amount of fuel. One way to possibly generate enough power is via nuclear fusion . However, the amount of fuel required for fusion would greatly increase the launch mass of an interstellar-bound spacecraft, meaning it would need even more fuel to get up to a velocity of 12% the speed of light as proposed by the British Interplanetary Society's Project Daedalus study . 

There is a way that a spacecraft could collect its fuel during its journey. The ionized hydrogen that fills the ISM is a perfect fuel for thermonuclear fusion. A spacecraft could, in principle, generate an immense cone-shaped magnetic field that extends ahead of the spacecraft, scooping up the ionized hydrogen, compressing it and funneling it down the mouth of the magnetic cone into the spacecraft's fusion reactor. Such an engine is called an interstellar ramjet, and is a concept that was invented by the fusion physicist Robert Bussard in 1960 and which is described in more detail by the Institute for Interstellar Studies .

It's not quite as simple as it sounds, though. The magnetic cone needs to be huge: in a higher-density region of the ISM, it needs an area of 3,860 square miles (10,000 square kilometers) emerging from an aperture 62 miles (100 km wide), while in a lower-density region, it would need a magnetic cone 3.8 million square miles (10 million square km) in area protruding from an aperture 186 miles (300 km across). The spacecraft would also have to be traveling fast enough in the first place to be able to rapidly scoop up enough of the diffuse hydrogen to generate a sufficient rate of fusion reactions; however calculations show that if a spacecraft could first accelerate to 2% of the speed of light it would begin to gather enough hydrogen to attain 50% of its potential thrust, and from that point on the ramjet could take over.

Students can learn more with this guide to the ISM from the European Space Agency. Follow the progress of the Voyagers in the final few years of their missions as they continue to explore interstellar space with NASA . Read more about a possible ' Interstellar Probe ' that would succeed the Voyagers and explore the interstellar medium beyond the heliopause on a 50-year mission.

Bibliography

The Road to the Stars by Iain Nicolson (William Morrow and Co., 1978)

Project Daedalus: The Final Report on the BIS Starship Study (Journal of the British Interplanetary Society, 1978)  

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Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

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