Subsystems on board a spacecraft serve various functions depending on its mission profile, such as:
Command and Data Handling (C&DH), also known as C&DH, entails receiving, validating, decoding and disseminating commands received from ground control in addition to transmitting telemetry data back down to Earth.
Attitude Determination and Control System (ADCS) employs electronic “eyes”, such as Sun and star trackers, rate gyros, control-moment gyros, rate gyros and control moment gyros to detect angular momentum and position the spacecraft accurately. ADCS also features reaction wheels for additional control over attitude control.
Propulsion
Propulsion systems convert electrical energy into kinetic energy and propel spacecraft forward, playing an essential role in its operation and helping Newton’s third law (“for every action there is an equal and opposite reaction”) come into play to bring it all home.
Electric Propellant Propulsion Systems (EPS) are an innovative new technology that utilizes electric power to generate thrust (or vectors), in order to keep orbits stable or perform maneuvers. They offer a highly cost-effective alternative to chemical propellants.
EPS electronics system comprises of a main microcontroller controlling global control algorithms and safety features while interfacing to OBC for interface. Four second-level controllers manage local subsystems. It has undergone vibration and thermal testing as well as full-scale plasma ignition tests encompassing 109 firing cycles.
Electrical and Power
No matter whether powered by solar energy, radioisotopes or nuclear reactors, electrical power must be produced, stored and distributed to spacecraft components. This power subsystem accounts for one-third of total mass and volume; its design must meet requirements for survivability, reliability, cost and power quality.
Space can provide energy sources such as electromagnetic radiation and changes to spacecraft potential that can power spacecraft missions, using SEEPS. Harnessing these resources requires using an appropriate subsystem like SEEPS for efficient use of its resources.
SEEPS is a system that harvests electricity from spacecraft environments by converting electromagnetic radiation into DC electrical current. The technology program for this subsystem emphasizes creating expert system software to manage aspects of its power subsystem.
Attitude and Orbit Control System (AOCS)
The Attitude and Orbit Control Subsystem (AOCS) ensures that satellites maintain proper posture in orbit for accurate pointing of payloads like scientific instruments, cameras, and communications equipment at their targets.
Sensors like gyroscopes, magnetometers and star trackers gather data about satellite orientation and position for use by control algorithms to command actuators to apply forces or torques that align them with their targets.
Ada is typically used to implement the software behind an AOCS, enabling complex software designs to be carried out on relatively small processors while being approved for space (i.e., passing an expensive process certifying their ability to withstand radiation, temperature range, launch shock and other environmental conditions). Alternatively, the AOCS may be integrated directly into the central satellite computer; autonomous mode transition decisions made onboard by on-board software may take precedence over commands sent from Earth via telecommand or vice versa.
Payload
Payload subsystems provide support for scientific instruments used by spacecraft missions, including Rosetta’s observation of cometary surfaces and Planck’s mapping variations in the Cosmic Microwave Background. Other examples of payload subsystems that enable spacecraft missions include Earth observing and navigation payloads such as radiometers on board SMOS satellites or CONSERT sensors aboard Galileo or EGNOS satellites for Earth observation or navigation missions.
Space can be an extremely harsh environment for delicate spacecraft components. Environmental subsystems help shield these pieces of equipment from extreme temperature variations and micrometeoroid impact damage by offering shielding protection from high velocity particles as well as an internal thermal control system to maintain stable temperatures throughout their mission.
Ground Segment
The ground segment refers to an arrangement of antennas and communications equipment which send commands to spacecraft as well as receive information back from it. It’s usually managed through a service provider.
Spacecraft and ground stations must communicate on the same frequency to work efficiently; this could be ultra high frequency (UHF), S, X or Ka. For optimal communication between these entities, an Automatic Orbit Control and Communication System (AOCS) uses sensors like star trackers, gyroscopes and magnetometers to track satellite orientation before activating actuators such as reaction wheels or magnetic torquers to alter it.
Telemetry, Tracking & Commanding (TT&C) software oversees command scripts sent to satellites as well as displays and analyses their telemetry data. Some services also offer expert teams for calibrating/validating, quality control and algorithm evolution activities; for instance Leaf Space provides a Ground-Segment-as-a-Service network tailored specifically for small satellites.