Shuttle simulator aircraft

While discussing the weather at the cape, NASA TV refered to and showed video of a “Shuttle Simulator Aircraft” or “Shuttle Training Aircraft” testing the wind at the landing site. It looked like a 707. Modified, I’m sure. What is it?

The official name is actually the Shuttle Training Aircraft (STA) and it’s a Grumman Gulfstream II.

Quite a bit smaller than a 707. 77 ft wingspan vs 145 ft.

Thanks. I just had a view down two engines mounted on the tail.