OP was talking about digital signatures and a hobbyist taking command of the spacecraft. In other words authentication. You said that was unnecessary and too t

OP was talking about digital signatures and a hobbyist taking command of the spacecraft. In other words authentication. You said that was unnecessary and too taxing on constrained hardware. That is incorrect. Authentication is both necessary and not excessively taxing, when both considering the risk to the spacecraft's operation or even not considering it, since, as you said yourself, authentication schemes can be reasonably lightweight. "Not out of the realm of possibility in satellites" What are you talking about? Of course it isn't! Authentication to satellites is recommended and implemented all the time, for obvious reasons. You think they risk a multi million dollar investment to save some clock cycles? How many commandeered satellites do you read about daily? Do you have sources to back up any of this?