Spacecraft
A
spacecraft is a vehicle designed to leave
Earth's atmosphere and operate beyond the surface of the Earth in
outer space. Spacecraft may either be
unmanned or
manned. Spacecraft are designed for a variety of missions which may include
communications,
earth observation,
meteorology,
navigation,
planetary exploration,
space tourism and
space warfare. The term spacecraft is also used to describe artificial
satellites.
A spacecraft is a system made up of various subsystems, dependent upon mission profile. Spacecraft subsystems may include: attitude determination and control (frequently called ADAC or ACS), guidance, navigation, and control (GNC or GN&C), communications (COMS), command and data handling (CDH or C&DH), power (EPS), thermal control (TCS), propulsion, structures, and payload. Manned spacecraft have the additional requirement of providing life support to the crew. Though not part of the spacecraft itself, the
launch vehicle used to place a spacecraft in orbit, and the ground system used to send
telecommands to the spacecraft and receive telemetry from the spacecraft, are frequently also considered subsystems. A
space suit has at times been called a miniature spacecraft.
Attitude control
Spacecraft need an
attitude control subsystem in order that they may 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.
GNC
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. On some missions, GNC and Attitude Control are combined into one subsystem of the spacecraft
Communications
The communications subsystem, sometimes called the Telemetry, Tracking, and Control (TT&C) subsystem serves as an interface between the spacecraft and the ground system, or between the spacecraft and other spacecraft. The communication subsystem receives telecommands from the ground subsystem, and transmits telemetry from the spacecraft.
Command and Data Handling
The CDH subsystem receives commands from the communications subsystem, performs validation and decoding of the commands, and distributes the commands the appropriate spacecraft subsystems and components. The CDH also receives housekeeping data and science data from the other spacecraft subsystems and components, and packages the data for storage on a Solid State Recorder or transmission to the ground via the communications subsystem. Other function of the CDH include maintaining the spacecraft clock and state-of-health monitoring (colloquially "watchdog").
Power
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 other spacecraft components. A
battery (or batteries) are typically connected to the bus via a battery charge regulator, and the battery is used to provide electrical power during periods when primary power is not available, for example when a
Low Earth Orbit (LEO) spacecraft is eclipsed by the Earth.
Thermal control
Spacecraft must be engineered to withstand transit through the
Earth's atmosphere and the
space environment. They must operate in a
vacuum with temperatures potentially ranging across hundreds of degrees
Celsius. Depending on mission profile, spacecraft may also need to operate on the surface of another planetary body.
Propulsion
Spacecraft may or may not have a
propulsion subsystem, depending upon whether or not the mission profile calls for propulsion. The
Swift spacecraft is an example of a spacecraft that does not have a propulsion subsystem. Typically though, LEO spacecraft (for example
Terra (EOS AM-1) include a propulsion subsystem for altitude adjustments (called drag make-up maneuvers) and
inclination adjustment maneuvers. A propulsion system is also needed for spacecraft that perform momentum management maneuvers. Components of a conventional propulsion subsystem include fuel, tankage, valves, pipes, and
thrusters. The TCS interfaces with the propulsion subsystem by monitoring the temperature of those components, and by pre-heating tanks and thrusters in preparation for a spacecraft maneuver.
Structures
Spacecraft must be engineered to withstand launch loads imparted by the launch vehicle, and must have a point of attachment for all the other subsystems. Depending upon 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.
Payload
The payload is dependent upon 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 system
The ground system, though not technically part of the spacecraft, is vital to the operation of the spacecraft. Typical components of a ground system in use during 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.
Launch vehicle
The launch vehicle is used propel the spacecraft from the Earth's surface, through the atmosphere, and into an
orbit, the exact orbit being dependent upon mission configuration. The launch vehicle may be
expendable or
reusable.
The term spacecraft is mainly used to refer to spacecraft that are real or conceived using present technology. The terms
spaceship and
starship are generally applied only to fictional spacecraft, usually those capable of
transporting people. The spaceship is one of the prime elements in
science fiction. Numerous
short stories and
novels are built up around various ideas for spacecraft, and spacecraft have often been featured in
movies. Some
hard science fiction books focus on the technical details of the craft, while others treat the spacecraft as a given and delve little into its actual implementation. Some of the most famous fictional spacecraft include the
USS Enterprise from
Star Trek, and the
Millennium Falcon from
Star Wars.
Some people believe that
Unidentified Flying Objects (UFOs) may be
alien spacecraft (that is, not of human construction and not originating from Earth), sometimes referred to as
flying saucers. But the term UFO used here in this context refers to observed flying objects for which no identification has been made, though
other meanings for the word UFO exist. To date, no known, independently verifiable examples of alien spacecraft are known to exist.
Manned spacecraft*
Apollo Spacecraft*
Gemini Spacecraft*
International Space Station*
Mir*
Mercury Spacecraft*
Shuttle Buran*
Shenzhou Spacecraft*
Space Shuttle*
Soyuz Spacecraft*
SpaceShipOne*
Voskhod Spacecraft*
Vostok SpacecraftHeaviest spacecraft*NASA
STS Space Shuttle/Orbiter - 109,000 kg or 120 tons (US)
|
A Russian Soyuz bringing a crew to the ISS |
Unmanned spacecraft*
Cassini-Huygens*
Cluster*
Deep Space 1*
Deep Impact (space mission)*ESA
SMART-1 Lunar Impact
*
Galileo*
Genesis*
Lunar Prospector*
Mars Exploration Rover*
Mars Global Surveyor*
Mars Pathfinder*
Near Earth Asteroid Rendezvous*
New Horizons*Soviet
Shuttle Buran (one mission only)
*
Pioneer 10*
Pioneer 11*
Progress*
SOHO*
Stardust*
Surveyor*
WMAPFarthest spacecraft*
Voyager 1 at 8.1 Billion miles
*
Pioneer 10 at 7.6 Billion miles
*
Voyager 2 at 6.5 Billion miles
Fastest spacecraft*
Helios I & II
Solar Probes - 158,000 mph or 43.9 miles per second
Spacecraft under development*
Automated Transfer Vehicle*
Crew Exploration Vehicle*
Kliper - Russian ' Clipper '
*
H-II Transfer Vehicle*India
Chandrayan-1 lunar probe
*
CNES Mars Netlander
*
James Webb Space Telescope - delayed
*
Kepler Mission Planet Searcher
*ESA
Darwin probe
*NASA
Dawn Mission probe
*
Herschel Space Observatory*
Mars Science Laboratory Rover
*
Phoenix Mars Scout
*
Shenzhou Cargo
Commercial spacecraft*
Genesis-1 inflated orbiting habitat (unmanned)
Commercial Spacecraft under development*Bristol
Ascender spaceplane
*
Rocketplane XP*ESA
Skylon SSTO
*
Space Adventures Explorer rocketplane
*Space Dev Dream Chaser
*
Space Ship Two*
SpaceX Dragon capsule
*
Virgin Galactic fleet
Cancelled spacecraft programs*
Apollo 18 through 21*China Project 921-3 Shuttle
*ESA
Hermes Shuttle
*Soviet
Buran Shuttle*Soyuz Kontakt 1
*
Terrestrial Planet Finder probe
*
ESA Eddington Telescope
*Mars Telecom Orbiter
Cancelled SSTO spacecraft*RR/British Aerospace
HOTOL*ESA
Hopper Orbiter
*McDonnell Douglas Clipper
DC-X*
Roton Rotored-Hybrid
*Lockheed-Martin
VentureStar*
Spacecraft Design*
Ansari X Prize*
Spaceflight Portal*
NASA*
ESA*
List of spaceflights*
NASA: Space Science Spacecraft Missions*Will Knight,
"Spacecraft skin 'heals' itself". January 2006, NewScientist.com.
*
Early History of Spacecraft
