Spacecraft are vehicles capable of transporting cargo or people beyond Earth’s atmosphere into space, consisting of a structural subsystem to bear launch vehicle loads as well as power, communications and navigation subsystems.
The navigation subsystem determines a spacecraft’s position and orientation within space. Additionally, it allows it to respond to commands transmitted from ground control.
Definition of a Spacecraft
Spacecraft are vehicles designed for travel through outer space, often piloted or unpiloted and capable of returning to Earth at certain points in its travels. Spacecraft are utilized for many different reasons including communications, Earth observation, meteorology, navigation and planetary exploration; some can even transport people and cargo.
All spacecraft require a propulsion subsystem in order to alter their trajectory in space, usually consisting of fuel, tanks, valves and thrusters. A thermal control system works alongside this subsystem in order to preheat tanks and thrusters prior to any maneuvers.
Spacecraft must also include an instrumentation subsystem to transmit data back to Earth – known as “telemetry.” Telemetry consists of both science data from experiments as well as engineering health measurements such as switch positions, voltages, temperatures and pressures; many measurements are recorded by sensor arrays which update every second; M&C (Mission Analysis Control and Monitoring) subsystem uses it as input into its command instructions for other subsystems.
Function of a Spacecraft
Spacecraft of any sort, whether satellites or vehicles that transport humans into space, must carry multiple systems for optimal operation. These depend on their mission type; power systems that convert solar energy to electric current are necessary in every spacecraft as is propulsion which ranges from chemical rockets and nuclear engines to more modern forms like ion drives.
The Command and Data Handling Subsystem (C&DH) is responsible for understanding and disseminating instructions from Earth. Additionally, C&DH maintains the spacecraft clock and metering system – essential in timekeeping commands uplinked from Earth – as well as gathering, processing and transmitting telemetry data back downlinking back to engineers on Earth.
All spacecraft require an effective communication system in order to connect with their operators, usually composed of antennae that transmit science data and telemetry back to Earth where engineers can assess its health as well as that of its payloads.
Subsystems of a Spacecraft
Spacecraft are composed of multiple subsystems that work together to keep it functional, such as Structure, Attitude Determination & Control, Onboard Data Handling, Communication Power Thermal Propulsion.
The structure subsystem is responsible for maintaining the mechanical integrity of spacecraft. It serves as the support structure, supporting all other spacecraft components while being engineered to endure stresses during launch, freefall flight and micrometeoroid impacts.
This subsystem manages the articulation of satellite components such as solar panels and high-gain antennas. Sensors, gyroscopes, and reaction wheels help maintain their orientation and stability in space.
This subsystem oversees a spacecraft’s command-data downlink from Earth and onboard storage devices, translating commands, identifying engineering and science data for downlink, formatting it for transmission, overseeing high-level fault protection as well as high-level fault protection. Additionally, its onboard computer also acts as a receiver collecting telemetry from other subsystems.
Types of Spacecraft
Spacecraft come in all forms ranging from unmanned probes to unmanned space capsules and spaceplanes, each requiring specific components for its mission profile. These may include propulsion systems (from traditional chemical rockets to ion drives and nuclear engines), command and data handling subsystems, attitude determination and control subsystems and structures.
Some spacecraft land on planets or moons using aerobraking, slowing their velocity by passing through their respective atmosphere. Other spacecraft employ parachute technology to inhibit free-fall; the Apollo Lunar Module used both these approaches when soft landing on the moon.
Orbiters spacecraft are designed to travel to distant planets and orbit them, using substantial propellant capability to slow it during the periods when shaded by the planet, as well as extreme thermal fluctuations. Furthermore, orbiter spacecraft must survive planetary occultations events which cut off uplink/downlink communications with Earth.