added as a fourth stage. The NASA X-43A hypersonic test vehicles were boosted by Pegasus first stages. The upper stages were replaced by exposed models of a scramjet-powered vehicle. The Orion stages boosted the X-43 to its ignition speed and altitude, and were discarded. After firing the scramjet and gathering flight data, the test vehicles also fell into the Pacific. The most numerous derivative of Pegasus is the booster for the Ground-based Midcourse Defense (GBMD) interceptor, basically a vertical (silo) launched Pegasus minus wing and fins, and with the first stage modified by addition of a Thrust Vector Control (TVC) system. Launch statistics Rocket configurations Launch sites Launch outcomes Carrier airplane Launch history Pegasus has flown 45 missions between 1990 and 2021. Planned launches Launch failures Flight F-6, 27 June 1994: The vehicle lost control 35 seconds into flight, telemetry downlink lost 38 seconds into flight, range safety commanded flight termination 39 seconds into flight. The likely reason for loss of control was improper aerodynamic modelling of the longer (XL) version of which this was the first flight. The Pegasus carried the DoD Space Test Program's satellite - Space Test Experiments Platform, Mission 1 (STEP-1). Flight F-9, 22 June 1995: The interstage ring between the 1st and 2nd stages did not separate, constraining movement of the 2nd-stage nozzle. As a result, the rocket deviated from its intended trajectory and was ultimately destroyed by range safety. The Pegasus carried the DoD Space Test Program's satellite - Space Test Experiments Platform, Mission 3 (STEP-3). Flight F-14, 4 November 1996: Failed to separate payloads because of a discharged battery intended to start separation pyros. Battery damage during launch was the likely reason. The lost payloads were the High Energy Transient Explorer and Argentina's SAC-B satellite. Partial successes Flight F-2, 17 July 1991: A faulty pyrotechnic system caused the rocket to veer off course during 1st-stage separation, resulting erratic maneuvers that prevented the rocket reaching the correct orbit, and the mission life, planned for 3 years, was reduced to 6 months. Flight F-5, 19 May 1994: A software navigation error caused the HAPS upper stage to shut down early, resulting in a lower than planned orbit. The Pegasus carried the DoD Space Test Program's satellite - Space Test Experiments Platform, Mission 2 (STEP-2). See also Air launch to orbit Comparison of orbital launchers families Comparison of orbital launch systems Pegasus II (rocket) References External