Not with the example given of NOAA satellites. Those simply broadcast data on regular intervals. If you had to authenticate, can you imagine a single satellite dealing with all the traffic of uplink/downlink required for authentication? It simply wouldn't work or maky any sense.

This is not true for all satellites, obviously. There are private ones that use encrypted communications, but weather satellites can be easily used if you have the proper antenna and equipment setup to do so.

Sure, SDR is the easy answer if you’re within LOS. But let’s assume I wanted to listen to another geosynchronous satellite that I wasn’t in LOS of.

Well, not quite free. Still gotta buy the wire, other supporting antenna hardware, and RTL-SDR lol

But yes, absolutely.