1.4 What? (Spacecraft Definition)

A spacecraft is a “vehicle or device designed for travel or operation outside the Earth’s atmosphere” [Merriam-Webster]. Spacecraft are commonly separated into seven engineering subsystems (Structure, Attitude Determination & Control, Onboard Data Handling, Communication, Power, Thermal, Propulsion) and a Payload.

Structure & Mechanisms

• • For large spacecraft, structures, mechanisms, and/or ordnance are often treated as separate subsystems.
  • Provides structural support to spacecraft components and spacecraft configuration.
  • Provides mechanical support for moving spacecraft elements (e.g., deploying and moving solar arrays, booms, or antennas).
  • Provides ordnance for separating or deploying movable components (usually, ordnance is explosive in nature, e.g., explosive bolts)

Electrical Power Subsystem

• • Supplies the spacecraft with the power required to sustain bus and payload operations.
  • Provides excess power that may be stored (in batteries) for later use.
  • All spacecraft must at least generate and distribute power.
  • For most spacecraft that do not venture beyond the orbit of Mars, power generation is usually accomplished via solar cells.
    

    

Command, (Telemetry, &) Data Handling

• • Receives, validates, decodes, and distributes commands to spacecraft systems.
  • Gathers, processes, formats, and records spacecraft housekeeping telemetry and payload data for downlink and/or use by the onboard computer (OBC).
  • All spacecraft must handle commands and data, even Sputnik, which had to send 1’s and 0’s across electronics to blink its light.

Communications/RF

• • Receives command data transmitted from a ground/space-based communications antenna.
  • Transmits telemetry data (containing spacecraft health and payload data) to ground/space-based receiving antennas.
  • All spacecraft must communicate with its operators; Sputnik blinked lights to know it had survived in space.

Attitude, Determination, Control, and Sensing

• • Senses changes in spacecraft orientation/stability.
  • Controls spacecraft or component (e.g., antenna or sensor) orientation as required to support payload/spacecraft pointing requirements.

Thermal (Monitoring &) Control

• • Maintains satellite components within required temperature limits by monitoring and heating/cooling components as required.

Propulsion

• • Stores and converts the potential energy of onboard propellant(s) into the propulsive energy needed to exert a required force(s) on a satellite.
    

    

Environment Control & Life Support

• • Provides control of the spacecraft environment to support humans and other required life forms by supplying oxygen, food, and potable water; maintaining comfortable temperatures; and removing, cleansing/ recycling waste products (gaseous, liquid & solid).
  • Thermal Control is sometimes included in the ECLSS.