Spacecraft telecommand overview
An essential part of operating a spacecraft is the ability to send telecommands from the ground to the spacecraft. The telecommand protocols include features to ensure that the telecommands arrive on-board the spacecraft:
- in order
- without gaps
- without duplication
- without errors
Uplink of telecommands
One element of the spacecraft control system on the ground is the TC Encoder. It takes commands and formats them into Communications Link Transmission Units (CLTUs) for uplink to the spacecraft. The encoder could be located in the operations control centre or in the ground station.
When the CLTUs reach the spacecraft they are processed by the on-board TC Decoder to extract the commands. The decoder also communicates with the encoder on the ground via Communications Link Control Words (CLCWs) which are included in the downlinked telemetry.
Our software products support spacecraft telecommand, including the TC Space Data Link Protocol, the Communications Operation Procedure-1 (COP-1) and the channel coding (BCH code). The protocols used to be known as Packet Telecommand.
Many missions use security, such as authentication and encryption, to protect the telecommand data. For example, authentication can protect a spacecraft against unauthorised commands.
Our telecommand products include products and options for security.