I'm curious about how the upload to these spacecrafts is secured. We're talking about 1977 technology. What prevents an antisocial troll or adversial state to upload broken firmware?
They are so far away now that you need a massive amount of radio power and a properly large dish to communicate with a SNR good enough for the onboard system to receive your transmission.
Right now I think the only dish in the world setup with the correct equipment to signal the Voyagers that is large enough is the Deep Space Network dish in Canberra, Australia.
This is correct accept that there are 3 DSN sites, Canberra, Madrid, and Ft. Irwin, California, each with a variety of different antennas. They're roughly spaced 120 degrees around the globe from each other so that full coverage of the sky is always maintained. Each has a 70m dish which I believe is the only antenna with enough gain to communicate with Voyager these days.
https://news.ycombinator.com/item?id=37093344