9.2 Subsystem Responsibilities

The Command and Data Handling (CDH) system is responsible for all of the spacecraft’s data processing needs (flight software) and the distribution of commands in hardware form (on-board computer system). CDH interacts with every component that outputs data (sensors, receiver) and receives commands (actuators, transmitter). The on-board computer and software is responsible for:

• • ingesting data from the payload.
  • storing payload data and spacecraft state of health data.
  • managing or coordinating the passing of data through the software pipeline.
    • This action may require on-board time synchronization.
  • receiving data from the receiver and passing data to the transmitter.
  • executing user commands and transition between user-dictated modes of operations (event sequencing).
  • monitoring health and performances of all subsystems.
  • handling mode transitions without user intervention.
  • detecting, isolating, and recovering from spacecraft failures, commonly reverting to a safe mode.

^{Spacecraft Technology: Failures in Electrical Systems and Software. Video by TU Delft Online Learning}

During the design process, the CDH specialist:

• • is the owner and primary developer of the spacecraft’s software architecture and on-board computer design.
  • is responsible for communicating with spacecraft bus components, which includes
    • converting raw data into sensible information
    • determining Input/Output requirements for the avionics subsystem with respect to the other subsystems, and payload
    • standardizing data packet formats across subsystems and across communication channels
  • coordinates with the systems engineer, other subsystem specialists, and mission operations to define the computer system’s operational modes and states.
  • manages the data budget and flow of data during operations by developing block diagrams that partition software scripts by function.
  • writes software to process, compress/decompress, and manipulate data.
  • strategizes with integration and test engineers in testing and verification of the spacecraft system.
  • encodes robustness in single-event upsets and information loss due to compression.