Command Handling

Command and Data Handling (C&DH) is the spacecraft subsystem responsible for managing commands, telemetry, onboard data, timing, and information flow between major systems. It connects the spacecraft's computers, sensors, payloads, communications equipment, and other hardware into a coordinated whole.

While individual subsystems perform specialized tasks, C&DH helps ensure that information reaches the correct destination at the correct time and that commands are interpreted and executed properly.

Command Processing

Commands may come from ground control or be generated by onboard software. Before execution, they can be checked, interpreted, prioritized, and scheduled to confirm that they are valid and suitable for the spacecraft's current condition.

Some commands execute immediately, while others are stored for a specific time or until certain conditions are met. This allows a spacecraft to carry out planned activities even when direct communication with Earth is unavailable.

Telemetry and Data

Spacecraft constantly produce information about their health and activities. Telemetry may include temperatures, power levels, system status, instrument activity, and other measurements that show how the vehicle is performing.

C&DH helps collect, organize, timestamp, store, and prepare this information for transmission. It may also manage scientific data produced by instruments and payloads until that information can be processed or sent to Earth.

Timing and Coordination

Many spacecraft activities must occur in a precise sequence. Instruments may need to operate at scheduled times, communication sessions must match available links, and some tasks depend on the condition of other systems.

Accurate onboard clocks and scheduling systems allow these operations to work together without unnecessary conflicts or demands on limited spacecraft resources.

Reliability and Recovery

Because C&DH supports so many essential functions, reliability is critical. Systems may include redundant hardware, error detection, health monitoring, and recovery procedures that help the spacecraft continue operating when problems occur.

During a serious anomaly, the spacecraft may suspend nonessential activities and enter a protective mode. It can preserve critical functions, monitor its condition, and attempt to reestablish communication with Earth.

Why C&DH Matters

Command and Data Handling provides the organizational framework behind spacecraft operations. By managing commands, telemetry, timing, storage, and information flow, it allows many independent components to operate together as one coordinated spacecraft.