On December 13, 1973, the American Space Agency, NASA, announced that it had selected the Gulfstream II to be used as a flying simulator for potential space shuttle crews. Grumman Aerospace Corporation was awarded a contract to modify two Gulfstream II aircraft to Shuttle Training Aircraft (STA). In order to simulate the flight characteristics and handling qualities of the much larger Space Shuttle Orbiter the aircraft were modified with in-flight thrust reversers, speed brakes and direct-lift flaps. The most obvious modification was the addition of two large side-force controls under the center section to simulate the lateral accelerations experienced in the Shuttle Orbiter. The STA's cockpit is divided into two, with the simulated Orbiter flight-deck on the left and the standard GII controls on the right.

The two aircraft purchased were c/n 146 and 147. Airframe 146 was registered with Grumman American as N879GA and made it's first flight on May 10, 1974. After initial flight tests it was delivered 'green' from Savannah (GA) to the Grumman Aerospace facility at Bethpage on Long Island (NY) via Houston (TX) on 20/21 May 1974. The aircraft was piloted by Cobb (GAAC) and Griggs (NASA). Prior to roll-out, after conversion to STA, the N897GA registration was cancelled and 146 was re-registered as N946NA. First flight in STA configuration was on September 29, 1975. Test-flights and demonstrations followed at Grumman's Peconic River Plant (Calverton (NY). Pilots on that first flight were Von der Heyden and Van Allen, both of Grumman. Almost a year later N946NA was delivered to Houston, Johnson Space Center, Ellington Field (TX) by NASA pilots Griggs and Mendenhall on September 15, 1976.

The second aircraft, c/n 147, first flew on June 5, 1974 and was delivered as N898GA from Savannah (GA) to Bethpage (NY) on June 13, 1974 by pilots Cobb (GAAC) and Algranti (NASA). First flight in STA configuration, with Von der Heyden and Van Allen of Grumman, on March 1, 1976, was followed by delivery to Houston, by NASA pilots Manson and Algranti on September 13, 1976. Both aircraft were based at the Johnson Space Center, Aircraft Operations Division facility at Ellington Air Force Base, Houston (TX). Most flights were done at the Northrup Strip, a dry-lake runway at the White Sands Missile Range in eastern New Mexico. Training missions were flown out of either El Paso international airport (TX) or Holloman Air Force Base (NM).

White Sands Space Harbor (WSSH) was used as one of the primary training areas for space shuttle pilots flying practice approaches and landings in the Shuttle Training Aircraft (STA). Set in dry gypsum lake beds, laser‐leveled runways prepared shuttle astronauts for final approaches and landings. Located on the White Sands Missile Range (WSMR), northeast of the NASA White Sands Test Facility, WSSH was originally called Northrup Strip and was chosen as a backup landing site in case of inclement weather at Edwards Air Force Base, California. On March 30, 1982, it was used as a landing site for Space Shuttle Columbia as it returned from its third orbital test flight. After that landing, former Apollo astronaut and New Mexico Senator Jack Schmitt introduced legislation in Congress to change the name from Northrup Strip to White Sands Space Harbor. The space harbor runways, navigational aids, and control facilities continuously stood ready providing contingency landing support for every shuttle mission. After the end of the Space Shuttle Program in 2011, WSSH was mothballed and in the summer of 2012 released the use of the property to WSMR. 

Subsequent missions were flown out of Edwards Air Force Base (CA) to te lakebed runway 17 from where the Space Shuttle Orbiter made its first flight.

A third aircraft, c/n 144, was purchased by NASA in 1983 for conversion to STA and registered N944GA and finally N944NA. This aircraft was born in 1974 as N17585 and flew with Swiss registration HB-ITR.  In 1989 another conversion was planned using a hybrid GII. NASA awarded a 4-million-dollar contract to Midcoast Aviation in St. Louis (MI) to produce a STA using the fuselage of c/n 118, which had been used by Lockheed for it's propfan research program, the wings from c/n 245 and the joined-wing box from a third airframe. The completed aircraft flew in STA configuration on December 20, 1990.