I mean the Voyager 1 probe which is currently the human-made object the farthest away from earth. The space program people operating the mission seem to have great control options, they even “moved software from one chip to another” (link) Apart from the probably gigantic and expensive installation needed to receive and/or send messages from/to that far away from home (23 hours of delay?), are there any safety measures to prevent a potentially malicous actor from sending commands to the probe?
That’s true. I just don’t know of a lot of mainstream things that have deployed it quite yet. Like I do not think HTTPS is post quantum secure, or at least not that I’m aware of.