Pegasus was an air-launched, small-lift launch vehicle developed by Orbital Sciences Corporation and later built and launched by Northrop Grumman. Pegasus was the world's first privately developed orbital launch vehicle. Capable of carrying small payloads of up to 443 kilograms (977 lb) into low Earth orbit, Pegasus first flew in 1990 and last flew before its retirement in 2026. It had primarily launched scientific satellites for NASA. The vehicle consisted of three solid-propellant stages and an optional monopropellant fourth stage. Pegasus used to be released from a carrier aircraft at about 40,000 feet (12,000 m) over open ocean, where it free-falls for five seconds before igniting its first-stage motor. The first stage did not have a thrust vectoring control system, instead using a delta wing and fins for lift and attitude control within the atmosphere. Pegasus initially used the NASA-owned B-52 Stratofortress named "Balls 8" as its carrier aircraft. By 1994, launches had transitioned to a modified L-1011 TriStar named "Stargazer" purchased by Orbital.
History Pegasus was designed by a team led by Antonio Elias. The Pegasus's three Orion solid motors were developed by Hercules Aerospace (later Alliant Techsystems) specifically for the Pegasus launcher but using advanced carbon fiber, propellant formulation and case insulation technologies originally developed for the terminated USAF Small ICBM program. The wing and fins' structures were designed by Burt Rutan and his company, Scaled Composites, which manufactured them for Orbital. Started in the spring of 1987, the development project was funded by Orbital Sciences Corporation and Hercules Aerospace, and did not receive any government funding. Government funding was received to support operational testing. NASA did provide the use of the B-52 carrier aircraft on a cost-reimbursable basis during the development (captive carry tests) and the first few flights. Two Orbital internal projects, the Orbcomm communications constellation and the OrbView observation satellites, served as anchor customers to help justify the private funding. There were no Pegasus test launches prior to the first operational launch on April 5, 1990, with NASA test pilot and former astronaut Gordon Fullerton in command of the carrier aircraft. Initially, a NASA-owned B-52 Stratofortress NB-008 served as the carrier aircraft. By 1994, Orbital had transitioned to their "Stargazer" L-1011, a converted airliner which was formerly owned by Air Canada. The name "Stargazer" is an homage to the television series Star Trek: The Next Generation: the character Jean-Luc Picard was captain of a ship named Stargazer prior to the events of the series, and his first officer William Riker once served aboard a ship named Pegasus. During its launch history, the Pegasus program had three mission failures (STEP-1, STEP-2 and HETI/SAC-B), and two partial failures, (USAF Microsat and STEP-2) followed by 30 consecutive successful flights for a total program success rate of 89 percent. The first partial failure on July 17, 1991, caused the seven USAF microsatellites to be delivered to a lower than planned orbit, significantly reducing the mission lifetime. The last mission failure on November 4, 1996, resulted in the loss of gamma-burst identifying satellite HETE-1 (High Energy Transient Explorer).
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