Shuttle Training Aircraft

The Shuttle Training Aircraft (STA) is a former NASA training vehicle that duplicated the Space Shuttle's approach profile and handling qualities, allowing pilots to simulate Shuttle landings under controlled conditions before attempting the task on board the orbiter. The STA was also flown to assess weather conditions just prior to Space Shuttle launches and landings.

Development
NASA developed the STA using the Grumman Gulfstream II as the underlying aircraft platform. During the early phases of the Shuttle program, NASA considered using the Boeing 737 airliner as the basis for the STA, but rejected it due to cost and opted for the less-expensive Gulfstream II.

The aircraft's exterior was modified to withstand the high aerodynamic forces incurred during training sorties. A redesigned cockpit provided a high-fidelity simulation of the Shuttle Orbiter's controls and pilot vantage point; even the seats were fitted in the same position as those in the Space Shuttle.

Operational history
The four STAs were normally located at the NASA Forward Operating Location in El Paso, Texas and rotated through Ellington Field (Houston, Texas) for maintenance. The STA was also used at Kennedy Space Center in Florida. It was primarily flown by astronauts practicing landings at the Shuttle Landing Facility and White Sands Space Harbor as well as to assess weather conditions prior to Space Shuttle launches and landings.

On December 3, 2003, a NASA Gulfstream II Shuttle Training Aircraft (STA) was flying a series of simulated shuttle landings to the Kennedy Space Center shuttle landing facility. On board the aircraft was an unidentified NASA astronaut pilot and two training personnel. The aircraft was on final approach at 13,000 feet when onboard instruments indicated a malfunction on one of the jet engine thrust reversers. The aircraft landed safely. A post-landing inspection showed that one of the 585-pound, 4-foot-wide, 5-foot-long thrust reversers had fallen off the aircraft. Divers later found the thrust reverser on the bottom of the nearby Banana River. An investigation showed that a bolt failed, releasing the part from the aircraft.

Flight profile
The STA was particularly critical for Shuttle pilots in training because the Orbiter lacked atmospheric engines that would allow the craft to "go around" after a poor approach. After re-entry, the Shuttle was a very heavy glider (it was affectionately referred to as a 'flying brick') and as such had only one chance to land successfully.

To match the descent rate and drag profile of the real Shuttle at 37000 ft, the main landing gear of the C-11A was lowered (the nose gear stayed retracted due to wind load constraints) and engine thrust was reversed. Its flaps could deflect upwards to decrease lift as well as downwards to increase lift.

Covers were placed on the left hand cockpit windows to provide the same view as from a Shuttle cockpit, and the left-hand pilot's seat was fitted with the same controls as a Shuttle. The STA's normal flight controls were moved to the right, where the instructor sat. Both seat positions had a head-up display (HUD).

In a normal exercise, the pilot descended to 20000 ft at an airspeed of 280 kn, 15 mi from the landing target. The pilot then rolled the STA at 12000 ft, 7 mi from landing. The nose of the aircraft was then dropped to increase speed to 300 kn, descending at a 20-degree angle on the outer glide slope (OGS). The outer glide slope aiming point was 7500 ft short of the runway threshold, and used PAPIs for visual guidance in addition to the MLS system. At 2000 ft the guidance system changed to pre-flare and shortly after, at 1700 ft, the pilot started the flare maneuver to gradually reduce the descent angle and transition to the inner glide slope (IGS) which was 1.5 degrees from 300 ft onwards, using a "ball-bar" system for visual guidance. The shuttle landing gear release was simulated at 300 ft above the ground, since the STA main gear remained down for the whole simulation. The nose gear of the STA was lowered at 150 ft AGL in case of an inadvertent touchdown with the runway surface.

If the speed was correct, a green light on the instrument panel simulated shuttle landing when the pilot's eyes were 32 ft above the runway. This was the exact position that the pilot's head would be in during an actual landing. In the exercise, the STA was still flying 20 ft above the ground. The instructor pilot deselected the simulation mode, stowed the thrust reversers, and the instructor executed a go-around, never actually landing the aircraft (on training approaches).

Avionics
A sophisticated computer system installed on board the STA simulated the flight dynamics of the orbiter with nearly perfect accuracy. The STA's highly realistic simulation of the orbiter was not limited to handling characteristics, but also implemented the shuttle control interfaces for the pilot.

An onboard computer called the Advanced Digital Avionics System (ADAS) controlled the Direct Lift Control (DLC) and the in-flight reverse thrust during Simulation Mode.

Every shuttle commander practiced at least 1,000 landings in this manner, as had each mission's shuttle pilot.

List of aircraft
Four Gulfstream II aircraft constituted the now retired STA fleet, although other Gulfstream II aircraft, lacking STA capabilities, are still used by NASA for personnel transport purposes. Although the majority of the fleet had markings similar to those pictured above, paint schemes do vary slightly across aircraft.

On August 22, 2011, NASA announced that all four Shuttle Training Aircraft would be retired at various NASA facilities around the country, with N944 retiring at the Dryden Flight Research Center.

The STA tail numbers were:
 * NASA 944: N944NA (s/n 144)
 * NASA 945: N945NA (s/n 118) — On July 13, 2017, a ribbon cutting ceremony was conducted and this aircraft is now in permanent display at the U.S. Space & Rocket Center in Huntsville, Alabama.
 * NASA 946: N946NA (s/n 146) — On September 21, 2011, this aircraft became a permanent display at the Texas Air & Space Museum in Amarillo, Texas.
 * NASA 947: N947NA (s/n 147) — Currently on permanent display at the Evergreen Aviation & Space Museum in McMinnville, Oregon.