So these satellites are no more complex than the amateur radio birds which function as simple FM repeaters?! Typically they'll have an uplink in the 2m band, and maybe a downlink in 70cm band, or the other way around. How can a military satellite be so casual in it's decision to relay audio? You'd think some authentication method would have been built in. I guess not?
Almost all comm sats are just bent pipes. Collisions are avoided via planning but that's just a gentleman's agreement at the end of the day. If you're watching with a spectrum analyzer and a decent dish it's pretty easy to see which transponders are currently idle.
The downside of course is that once you start hitting a satellite with a signal they know exactly where you are and the operators will call the cops on you. Your signal is not only potentially interfering with someone who paid for the transponder, but it also impacts their energy budget.
I've been told that if you rent a transponder it's important to put a signal up on it pretty quickly, otherwise pirates will attempt to "borrow" it from you, and they can be hard to evict.
What I know about this comes from some training I took for my job. The training came from the equipment vendor, but the instructor was also an operator so he knew the ins and outs of the system.
There is a lot to cover, from calculating link budgets, scramble codes (related to anti-jam), waveforms, pointing a dish, calculating frequencies, reading channel allocation docs, tradeoffs of different frequency bands, etc... However, the basics are pretty basic. You modulate a series of bits onto a carrier at a specific frequency and radiate it at a specific point in the sky. The transponder on the satellite amplifies the signal, shifts it a fixed number of Mhz, and retransmits it back towards the Earth.
There are some satellites that act like flying routers and actually decode the packet back into bits before re-encoding it for transport, but generally the added complexity has made this approach unpopular. One constellation that does this is Iridium, because it then forwards packets between satellites until it can be downlinked to the ground.
Not particularly. They're all in fixed known orbits so each satellite would know at any given time where all the other satellites in it's constellation will be so it can know what satellites will have the best signal between it and the downlink. With that all you really need is for the phones to ping the satellites every couple minutes while on to update the what satellites are over head of phone X. (You could even be clever and cheat a little by figuring out the rough coordinates of each handset and then figure out roughly what satellites would be near overhead too since handsets generally don't move very quickly.)
Maybe the military prefers the simple over the complex. It's a lot simpler to change authentication methods in ground equipment than in orbital equipment.
Think back to the state of the art in the 70s when these were thought up. You can cite SIGSALY[1] but it took a really long time for these concepts to be flyable. AT&T was doing digital telephony terrestrially in the 60s [2] but radio links make this more difficult. Of course things are different today.
You could have a DSP kind of repeater where the satellite receives a signal, unencrypts it, reads the information inside the packet, encrypts it, and the routes it accordingly (maybe to a different antenna or to the avionics computer inside). The old designs were basically just two antennas with an amplifier in between them. If you wanted encryption, that was between you and the recipient. The satellite was pretty much agnostic to what was going through it. The benefit of even the simplest digital repeater is that your signal only has to be good enough for a one way trip. You can do higher data rates because you only need to worry about the space to ground link (ground to space usually isn't a problem since power is more available).
