I.B. + M.A. DE LANDE LONG
SOFTWARE + CONSULTANCY

Spacecraft Packet Telecommand Overview

An essential part of operating a spacecraft is the ability to send telecommands from the ground to the spacecraft. The TC Space Data Link Protocol of Spacecraft Packet Telecommand is designed to ensure that the telecommands arrive on-board the spacecraft

in order
without gaps
without duplication
without errors

Spacecraft telecommand

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.

The Spacecraft Packet Telecommand standard is defined by the CCSDS recommendations and ECSS and ESA standards. By defining the standard, these organisations aim to

enable improved telecommand capability, such as higher throughput
reduce mission costs
enable greater cross-support for missions between different space agencies

It achieves this by encouraging the development and availability of components such as our telecommand products which support the standard.

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