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Training aircraft for the Space Shuttle

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.

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.

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 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 feet (11278 m), 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 feet (6096 m) at an airspeed of , 15 mile (24 km) from the landing target. The pilot then rolled the STA at 12000 feet (3658 m), 7 mile (11 km) from landing. The nose of the aircraft was then dropped to increase speed to , descending at a 20 degree angle on the outer glide slope (OGS). The outer glide slope aiming point was 7500 feet (2286 m) short of the runway threshold, and used PAPIs for visual guidance in addition to the MLS system. At 2000 feet (610 m) the guidance system changed to pre flare and shortly after, at 1700 feet (518 m), 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 feet (91 m) onwards, using a "ball bar" system for visual guidance. The shuttle landing gear release was simulated at 300 feet (91 m) above the ground, since the STA main gear remained down for the whole simulation. The nose gear of the STA was lowered at 150 feet (46 m) 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 feet (10 m) 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 feet (6 m) 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).

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.