Basically everything any Pentagon official could have dreamed of, for $70M? Probably the fastest check ever written there (yes yes it's just the beginning but you get the idea.)
It’s very likely harder to jam, but unjammable is a very bold statement.
It seems to add up to a pretty dang hardened looking system? Cyberattacks, sabotage and so on could be real concerns, but to jam a tight beam phased array looking at very specific spots for signal from 10-100 miles away looks hard from a physics point of view. And of course any powerful jammer will by definition be an absolute magnet for HARMs. The US takes SEAD/DEAD very seriously and is thus pretty heavily equipped for that.
Jamming DownLink is certainly difficult especially if ground terminal uses receiver beam steering and pointing upwards. Jamming UpLink is easier by beaming directly at the satellites' receiver antennas. Jammers can use beam steering too.
>Jammers can use beam steering too.
Beam steering doesn't make the beams curve though. The satellites know where the terminals are, and last I checked they do 8 or 16 beams and current beam spot size is 22km in diameter (and set to shrink with full size v2 and future, that's key to improving density of service). Which means your jammer would need to be tracking the right satellites without help from the satellites themselves (unlike real terminals), and within 22km (or far, far less, and on the correct side of the cell) of the terminal. I invite you to compare that to the range of basic 155mm artillery, GMLRS missiles, JDAMs, HARMs, or other such weapon systems, and remember we're talking about this in a military context. Is a jammer that has to be so close it gets destroyed right away militarily significant?