Pegasus RocketOrbital Sciences Pegasus rocket model. Pegasus XL is a winged, three stage, solid rocket booster which weighs approximately 23,130 kg (51,000 lbm) and measures 16. 9 m (55. 4 ft) in length and 1. 27 m (50 in) in diameter and has a wing span of 6. 7 m (22 ft). It is lifted by an L 1011 carrier aircraft to a level flight condition of about 11,900 m (39,000 ft) and Mach 0. 80. Five seconds after release from the aircraft Stage 1 motor ignition occurs.