system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't bad guys, rogue nations, hackers commandeer Voyager 2, et al?

I haven't found a comprehensive look at what sorts of layers of security go into safeguarding these vessels. I read an article of some antennas being used to communicate with Voyager 2 while her usual terrestrial antenna is repaired. Ok, but what's to stop anyone else from communicating in the interim? Or ever? Is it locked frequencies? Very specific API requiring perfect names, function calls, encryption keys? What exactly do space-level security and encryption mean?  How does this age?

&#x200B;

Thanks!!
gpt
To communicate with Voyager, we have to use very big radios.  These radios are run by the NASA Deep Space Network.

They are in Australia, Spain, and the USA, because then, at least one is on the side of the Earth that can see the part of the sky you're talking to.

The telescopes they have to use are HUGE.  The Madrid station has several that are 34 meters across, and the main one is a big bowl 70 meters across!  That's as big as a jumbo jet!

Nobody else can communicate with Voyager because radios that large are very expensive, and they're the only way we can.