SPACE CRAFT

A spacecraft is a craft or machine designed for spaceflight. On a spaceflight, a spacecraft enters space then returns to the Earth. For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body. Spacecraft used for human spaceflights carry people on board as crew or passengers. Spacecraft used for robotic space missions operate either autonomously or electromagnetically. Robotic spacecraft that leave the vicinity of the planetary body are space probes. Robotic spacecraft that remain in orbit around the planetary body are artificial satellites. Starships, which are built for interstellar travel, are so far a theoretical concept only. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and space tourism. Spacecraft and space travel are common themes in works of spacecraft subsystems A spacecraft system comprises various subsystems, dependent upon mission profile. Spacecraft subsystems may include: attitude determination and control (variously called AD AC, ADC or SACS), guidance, navigation and control (ENC or GEN&C), communications (CORMS), command and data handling (CH or C&DH), power (ESP), thermal control (TICS), propulsion, structures, and payload. Spacecraft intended for human spaceflight must also include a life support system for the crew. This can include many different types of Oxygen Systems, such as the one seen in the movie Apollo 13 that exploded and almost cost the crew their lives.

Spacecraft could do with 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 meant for the science objective, sun pointing for supremacy to the cosmological arrays furthermore earth-pointing for communications. Guidance refers to the calculation of the commands (usually done by the CH 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 get together mission requirements. On some missions, ENC and Attitude Control are combined interested in individual subsystem of the spacecraft.

The CH 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 CH 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 passing through the communications subsystem. Other functions of the CH include maintaining the spacecraft clock in addition to state-of-health monitoring.

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 (RT) 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. Batteries are typically connected to the bus via a battery charge regulator, and the batteries are 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 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 be and C-C or (possibly due to the lower thickness requirements despite its high density) W or ablative C-C composites are used. Depending on mission profile, spacecraft may also 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 louvers to control temperature ranges of equipments within specific ranges. Science fiction.