A spacecraft is a vehicle, or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo.
On a sub-orbital spaceflight, a spacecraft enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around additional celestial bodies. Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit (space stations) only, whereas those used for robotic space missions operate either autonomously or telerobotically. Robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a planetary body are artificial satellites. Only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, and New Horizons, are on trajectories that leave the Solar System.
Humanity has achieved space flight but only a few nations have the technology for orbital launches, including: Russia (Roskosmos), the United States (NASA), the member states of the European Space Agency (ESA), Japan (JAXA), India (ISRO), and China (CNSA).
Sputnik was the first artificial satellite. It was launched into an elliptical low Earth orbit (LEO) by the Soviet Union on 4 October 1957. The launch ushered in new political, military, technological, and scientific developments; while the Sputnik launch was a single event, it marked the start of the Space Age. Apart from its value as a technological first, Sputnik additionally helped to identify the upper atmospheric layer's density, through measuring the satellite's orbital changes. It additionally provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen in the satellite's false body provided the first opportunity for meteoroid detection. Sputnik 1 was launched throughout the International Geophysical Year from Site No.1/5, at the fifth Tyuratam range, in Kazakh SSR (now at the Baikonur Cosmodrome). The satellite travelled at 29,000 km (18,000 mi) per hour, taking 96.2 minutes to complete an orbit, and emitted radio signals at 20.005 and 40.002 MHz
While Sputnik 1 was the first spacecraft to orbit the Earth, additional man-made objects had previously reached an altitude of 100 km, which is the height required by the international organisation Fédération Aéronautique Internationale to count as a spaceflight. This altitude is called the Kármán line. In particular, in the 1940s there were several test launches of the V-2 rocket, a few of which reached altitudes well over 100 km.
Past and present spacecraft
As of 2016, only three nations have flown manned spacecraft: USSR/Russia, USA, and China. The first manned spacecraft was Vostok 1, which carried Soviet cosmonaut Yuri Gagarin into space in 1961, and completed a full Earth orbit. There were five additional manned missions which used a Vostok spacecraft. The second manned spacecraft was named Freedom 7, and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 km (116 mi). There were five additional manned missions using Mercury spacecraft.
Other Soviet manned spacecraft include the Voskhod, Soyuz, flown unmanned as Zond/L1, L3, TKS, and the Salyut and Mir manned space stations. Other American manned spacecraft include the Gemini Spacecraft, Apollo Spacecraft, the Skylab space station, and the Space Shuttle with undetached European Spacelab and private US Spacehab space stations-modules. China developed, but didn't fly Shuguang, and is currently using Shenzhou (its first manned mission was in 2003).
Except for the space shuttle, all of the recoverable manned orbital spacecraft were space capsules.
The International Space Station, manned after November 2000, is a joint venture between Russia, the United States, Canada and several additional countries.
Some reusable vehicles have been designed only for manned spaceflight, and these are often called spaceplanes. The first example of such was the North American X-15 spaceplane, which conducted two manned flights which reached an altitude of over 100 km in the 1960s. The first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19, 1963.
The first partially reusable orbital spacecraft, a winged non-capsule, the Space Shuttle, was launched by the USA on the twentieth anniversary of Yuri Gagarin's flight, on April 12, 1981. During the Shuttle era, six orbiters were built, all of which have flown in the atmosphere and five of which have flown in space. Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 SCA and gliding to deadstick landings at Edwards AFB, California. The first Space Shuttle to fly into space was Columbia, followed by Challenger, Discovery, Atlantis, and Endeavour. Endeavour was built to replace Challenger when it was lost in January 1986. Columbia broke up throughout reentry in February 2003.
The first automatic partially reusable spacecraft was the Buran (Snowstorm), launched by the USSR on November 15, 1988, although it made only one flight and this was unmanned. This spaceplane was designed for a crew and strongly resembled the U.S. Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR, prevented any further flights of Buran. The Space Shuttle was subsequently modified to allow for autonomous re-entry in case of necessity.
Per the Vision for Space Exploration, the Space Shuttle was retired in 2011 due mainly to its old age and high cost of programme reaching over a billion dollars per flight. The Shuttle's human transport role is to be replaced by Space X's Dragon V2 and Boeing's CST-100 Starliner no later than 2017. The Shuttle's heavy cargo transport role is to be replaced by expendable rockets such as the Space Launch System and SpaceX's Falcon Heavy.
Scaled Composites' SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize. The Spaceship Company will build its successor SpaceShipTwo. A fleet of SpaceShipTwos operated by Virgin Galactic was planned to start reusable private spaceflight carrying paying passengers in 2014, but was delayed after the VSS Enterprise crash.
Designed as manned but flown as unmanned only spacecraft
- Zond/L1 – lunar flyby capsule
- L3 – capsule and lunar lander
- TKS – capsule
- Buran-class shuttle – Soviet shuttle
Semi-manned – manned as space stations or part of space stations
- Progress – unmanned USSR/Russia cargo spacecraft
- TKS – unmanned USSR/Russia cargo spacecraft and space station module
- Automated Transfer Vehicle (ATV) – unmanned European cargo spacecraft
- H-II Transfer Vehicle (HTV) – unmanned Japanese cargo spacecraft
- SpaceX Dragon – unmanned private spacecraft
- Tianzhou 1(spacecraft) – China's unmanned spacecraft
- Explorer 1 – first US satellite
- Project SCORE – first communications satellite
- SOHO - orbits the Sun near L1
- Sputnik 1 – world's first artificial satellite
- Sputnik 2 – first animal in orbit (Laika)
- Sputnik 5 – first capsule recovered from orbit (Vostok precursor) – animals survived
- Syncom – first geosynchronous communications satellite
- Hubble Space Telescope – largest orbital observatory
- X-37 – spaceplane
- Clementine – US Navy mission, orbited Moon, detected hydrogen at the poles
- Kaguya JPN – Lunar orbiter
- Luna 1 – first lunar flyby
- Luna 2 – first lunar impact
- Luna 3 – first images of lunar far side
- Luna 9 – first soft landing on the Moon
- Luna 10 – first lunar orbiter
- Luna 16 – first unmanned lunar sample retrieval
- Lunar Orbiter – quite successful series of lunar mapping spacecraft
- Lunar Prospector – confirmed detection of hydrogen at the lunar poles
- Lunar Reconnaissance Orbiter – Identifies safe landing sites & Locates moon resources
- Lunokhod - Soviet lunar rovers
- SMART-1 ESA – Lunar Impact
- Surveyor – first USA soft lander
- Chang'e 1 – China's Chang'e Lunar mission
- Chang'e 2 – China's Chang'e Lunar mission
- Chang'e 3 – China's Chang'e Lunar mission
- Chang'e 4 – China's Chang'e Lunar mission
- Chang'e 5 – China's Chang'e Lunar mission
- Chang'e 6 – China's Chang'e Lunar mission
- Chandrayaan 1 – First Indian Lunar mission
- Akatsuki JPN – a Venus orbiter
- Cassini–Huygens – first Saturn orbiter + Titan lander
- Curiosity rover – Rover sent to Mars by NASA in 2012
- Galileo – first Jupiter orbiter+descent probe
- IKAROS JPN – first solar-sail spacecraft
- Mariner 4 – first Mars flyby, first close and high resolution images of Mars
- Mariner 9 – first Mars orbiter
- Mariner 10 – first Mercury flyby, first close up images
- Mars Exploration Rover – a Mars rover
- Mars Express – a Mars orbiter
- Mars Global Surveyor – a Mars orbiter
- Mars Orbiter Mission - India's first Interplanetary probe.
- Mars Reconnaissance Orbiter – an advanced climate, imaging, sub-surface radar, and telecommunications Mars orbiter
- MESSENGER – first Mercury orbiter (arrival 2011)
- Mars Pathfinder – a Mars lander + rover
- New Horizons – first Pluto flyby (arrival 2015)
- Pioneer 10 – first Jupiter flyby, first close up images
- Pioneer 11 – second Jupiter flyby + first Saturn flyby (first close up images of Saturn)
- Pioneer Venus – first Venus orbiter+landers
- Vega 1 – Balloon release into Venus atmosphere and lander (joint mission with Vega 2), mothership continued on to fly by Halley's Comet
- Venera 4 – first soft landing on another planet (Venus)
- Viking 1 – first soft landing on Mars
- Voyager 2 – Jupiter flyby + Saturn flyby + first flybys/images of Neptune and Uranus
Other – deep space
- Deep Space 1
- Deep Impact
- Near Earth Asteroid Rendezvous
- STEREO – Heliospheric and solar sensing; first images of the entire Sun
- Helios I & II Solar Probes (252,792 km/h or 157,078 mph)
Furthest spacecraft from the Sun
- Pioneer 10 at 114.07 AU as of January 2016, travelling outward at about 2.54/year
- Pioneer 11 at 111.4 AU as of July 2015, travelling outward at about 2.4 AU/year
- Voyager 1 at 135.7 AU as of August 2016, travelling outward at about 3.6 AU/year
- Voyager 2 at 111.4 AU as of August 2016, travelling outward at about 3.3 AU/year
Unfunded and cancelled programs
- Shuguang – Chinese capsule
- Soyuz Kontakt – USSR capsule
- Almaz – USSR space station
- Manned Orbiting Laboratory – US space station
- Altair – US lunar lander of Orion spacecraft
- X-20 – US shuttle
- Soviet Spiral Shuttle
- Soviet Buran Shuttle
- ESA Hermes shuttle
- Kliper Russian semi-shuttle/semi-capsule
- Japanese HOPE-X shuttle
- Chinese Shuguang Project 921-3 shuttle
- RR/British Aerospace HOTOL
- ESA Hopper Orbiter
- McDonnell Douglas DC-X (Delta Clipper)
- Roton Rotored-Hybrid
- Lockheed-Martin VentureStar
Spacecraft under development
- (US-NASA) Orion Multi-Purpose Crew Vehicle – capsule
- (US-SpaceX ) Dragon V2 – capsule
- (US-Boeing) CST-100 – capsule
- (US-Sierra Nevada Corporation) Dream Chaser – orbital spaceplane
- (US-The SpaceShip company)SpaceShipTwo suborbital spaceplane
- (US-Blue Origin) New Shepard – VTVL capsule
- (US-XCOR) Lynx rocketplane – suborbital spaceplane
- China Shenzhou 3 spacecraft Cargo
- China Shenzhou 4 spacecraft Cargo
- China Shenzhou 5 spacecraft Cargo
- China Shenzhou 6 spacecraft Cargo
- China Shenzhou 7 spacecraft Cargo
- China Shenzhou 8 spacecraft Cargo
- China Shenzhou 9 spacecraft Cargo
- China Shenzhou 10 spacecraft Cargo
- (India-DRDO) Avatar RLV -Under development, First demonstration flight planned in 2015.
- (India-ISRO) Orbital Vehicle – capsule
- (India-ISRO) RLV Technology Demonstration Programme - Spacecraft
- SpaceX reusable rocket
- (Russia-RKA) Prospective Piloted Transport System (PPTS) – capsule
- (Europe-ESA) Advanced Crew Transportation System – capsule
- (Iranian Space Agency) Orbital Vehicle – capsule
- SpaceX Dragon – cargo delivery to the ISS
- Orbital Sciences Cygnus – cargo delivery to the ISS
- CNES Mars Netlander
- James Webb Space Telescope (delayed)
- ESA Darwin14 probe
- Mars Science Laboratory rover
- China Shenzhou 1 spacecraft Cargo
- China Shenzhou 2 spacecraft Cargo
- Terrestrial Planet Finder cancelled probe
- System F6—a DARPA Fractionated Spacecraft demonstrator
- Reaction Engines Limited Skylon (spacecraft)
A spacecraft system comprises various subsystems, depending on the mission profile. Spacecraft subsystems comprise the spacecraft's "bus" and might include attitude determination and control (variously called ADAC, ADC, or ACS), guidance, navigation and control (GNC or GN&C), communications (comms), command and data handling (CDH or C&DH), power (EPS), thermal control (TCS), propulsion, and structures. Attached to the bus are typically payloads.
- Life support
- Spacecraft intended for human spaceflight must additionally include a life support system for the crew.
- Attitude control
- A Spacecraft needs an attitude control subsystem to be correctly oriented in space and respond to external torques and forces properly. The attitude control subsystem consists of sensors and actuators, together with controlling algorithms. The attitude-control subsystem permits proper pointing for the science objective, sun pointing for power to the solar arrays and earth pointing for communications.
- Guidance refers to the calculation of the commands (usually done by the CDH subsystem) needed to steer the spacecraft where it is desired to be. Navigation means determining a spacecraft's orbital elements or position. Control means adjusting the path of the spacecraft to meet mission requirements.
- Command and data handling
- The CDH subsystem receives commands from the communications subsystem, performs validation and decoding of the commands, and distributes the commands to the appropriate spacecraft subsystems and components. The CDH additionally receives housekeeping data and science data from the additional spacecraft subsystems and components, and packages the data for storage on a data recorder or transmission to the ground via the communications subsystem. Other functions of the CDH include maintaining the spacecraft clock and state-of-health monitoring.
- Spacecraft, both robotic and crewed, utilise various communications systems for communication with terrestrial stations as well as for communication between spacecraft in space. Technologies utilised include RF and optical communication. In addition, a few spacecraft payloads are explicitly for the purpose of ground–ground communication using receiver/retransmitter electronic technologies.
- Spacecraft need an electrical power generation and distribution subsystem for powering the various spacecraft subsystems. For spacecraft near the Sun, solar panels are frequently used to generate electrical power. Spacecraft designed to operate in more distant locations, for example Jupiter, might employ a radioisotope thermoelectric generator (RTG) to generate electrical power. Electrical power is sent through power conditioning equipment before it passes through a power distribution unit over an electrical bus to additional spacecraft components. Batteries are typically connected to the bus via a battery charge regulator, and the batteries are used to provide electrical power throughout periods when primary power isn't available, for example when a low Earth orbit spacecraft is eclipsed by Earth.
- Thermal control
- Spacecraft must be engineered to withstand transit through Earth's atmosphere and the space environment. They must operate in a vacuum with temperatures potentially ranging across hundreds of degrees Celsius as well as (if subject to reentry) in the presence of plasmas. Material requirements are such that either high melting temperature, low density materials such as beryllium and reinforced carbon–carbon or (possibly due to the lower thickness requirements notwithstanding its high density) tungsten or ablative carbon–carbon composites are used. Depending on mission profile, spacecraft might additionally need to operate on the surface of another planetary body. The thermal control subsystem can be passive, dependent on the selection of materials with specific radiative properties. Active thermal control makes use of electrical heaters and certain actuators such as louvres to control temperature ranges of equipments within specific ranges.
- Spacecraft propulsion
- Spacecraft might or might not have a propulsion subsystem, depending on whether or not the mission profile calls for propulsion. The Swift spacecraft is an example of a spacecraft that doesn't have a propulsion subsystem. Typically though, LEO spacecraft include a propulsion subsystem for altitude adjustments (drag make-up maneuvers) and inclination adjustment maneuvers. A propulsion system is additionally needed for spacecraft that perform momentum management maneuvers. Components of a conventional propulsion subsystem include fuel, tankage, valves, pipes, and thrusters. The thermal control system interfaces with the propulsion subsystem by monitoring the temperature of those components, and by preheating tanks and thrusters in preparation for a spacecraft maneuver.
- Spacecraft must be engineered to withstand launch loads imparted by the launch vehicle, and must have a point of attachment for all the additional subsystems. Depending on mission profile, the structural subsystem might need to withstand loads imparted by entry into the atmosphere of another planetary body, and landing on the surface of another planetary body.
- The payload depends on the mission of the spacecraft, and is typically regarded as the part of the spacecraft "that pays the bills". Typical payloads could include scientific instruments (cameras, telescopes, or particle detectors, for example), cargo, or a human crew.
- Ground segment
- The ground segment, though not technically part of the spacecraft, is vital to the operation of the spacecraft. Typical components of a ground segment in use throughout normal operations include a mission operations facility where the flight operations team conducts the operations of the spacecraft, a data processing and storage facility, ground stations to radiate signals to and receive signals from the spacecraft, and a voice and data communications network to connect all mission elements.