[mendigou]

There are normally at least two radio links: telemetry and telecommand. Some spacecraft have multiple of each, with at least one channel of each being some sort of emergency channel where you can only do the most basic ops or get the most basic data.

As the sibling comment mentions, command signals are normally at least signed, and many times also encrypted.

Telemetry is way less sensitive, so it is usually not encrypted in scientific missions. There are well known protocols for space communications (e.g. CCSDS, PUS), so once you figure out a few fields you can make educated guesses of what each byte is. A previous post of the linked blog discusses it in detail: https://destevez.net/2020/08/tianwen-1-telemetry-framing-and...

Even without the actual telemetry, there are many things you can guess about the satellite attitude from just observing the radio signal. Many satellite and radio amateurs love doing that!