flightaware.com/live/flight/NASA843
Edited
Uh oh, you started this same thread less than 24 hours ago:
I assume since this is NASA that this flight is real.
ICE21 is another F18 (and sometimes F16 or A10) flight.
If you look at NASA 836 it hit a ground speed of over 900 Knots.
Is that possible and if so what GS is needeed to break the sound barrier?
If you look again, you will see that it didn’t hit the ground, it was still at FL410 when the track ended.
And Mach speed has nothing to do with ground speed. It has to do with your speed relative to the air around you, plus the atmospheric conditions of that air. But at 900 knots GS, it is probably a safe bet that it was Mach 1+, since that is over 1,000 MPH, unless there was some pretty crazy wind that day.
Read it again Newark.
Haha, brain fart on my part.
Second paragraph still applies, though. 
While we’re waiting for his neurons to process the info, I saw 721AF heading into MMU earlier today, low and fast!
Awesome.