TC

Used for the uplink (ground to satellite). TC frames are variable-length (up to a configured maximum). The header contains SCID, VCID, frame sequence number, and two flags:

• Bypass flag: when set, the frame bypasses the COP-1 sequence check and is delivered immediately. Used for emergency commands when the COP-1 state may be out of sync.
• Control flag: distinguishes command frames (carrying Space Packets) from control frames (carrying COP-1 directives).

TC frames are typically much shorter than TM frames because commands are small and uplink bandwidth is limited.