Data handling system interprets commands from Earth, collects, processes and formats the telemetry data, which is to be returned to Earth. The main parts of this sub-system are
Spacecraft clock: A counter maintained by the command and data subsystem. It meters the passing of time during the life of the spacecraft, and regulates nearly all activity within the spacecraft systems. Many types of commands uplinked to the spacecraft are set to begin execution at specific spacecraft clock counts.
Telemetry: The system for radioing information from a spacecraft to the ground. Telemetry is typically a mixture of science data from the experiments and spacecraft engineering or health data. Engineering or health data is composed of a wide range of measurements, from switch positions and subsystem states to voltages, temperatures and pressures. Telemetry may be transmitted in real time, or it may be written to a data storage device until transmission is feasible.
Tape recorder: A mechanical device for recording digital information on magnetic tape and for playing back the recorded material. The stored data can be played back for downlink when receiving station resources are available.
Fault protection: This system has the ability to reestablish contact with Earth if a mishap occurs and contact is interrupted.