EDIT: Haven’t found the source. I did find that the existing ViaSat-1 latency (on Exede, and actual ping times not satellite->ground latency) is 600 to 700ms, so that’s roughly in line with what you said. Exede do a bunch of latency compensation where they can so people often report lower latency, but for eg online games that obviously won’t work.
I also know that what I read before was specific to airplane in-flight internet, although I doubt commercial flight altitude make any difference to latency, so that’s likely an irrelevant point.
Edit: unless you're doing sigint in something very fast, like a missile launch.
"Active SIGINT" really only applies to CNE and not the traditional COMINT where MITM is used for translation and interpretation. In which case latency does matter, but not on the order of ms.
unless you're doing sigint in something very fast, like a missile launch.
That's FISINT/ELINT/MASINT though and has a completely different PED chain. Almost 100% automated.
Given that the recently launched civillian satellite Viasat-2 has a bandwidth of 300Gb/s and a reported expected latency of about 25ms, its not hard to imagine that a classified satellite like this may have crazy high bandwidth and low latency, perfect for reconnaissance, SIGNINT or operating UAVs.