Pegasus

Vehicle Configurations

Vehicle Components

Pegasus, the world's only winged, drop-launched space launch vehicle, was developed during the late 1980s and early 1990s by Orbital Sciences Corporation and Hercules Aerospace. The original design that first flew in 1990 was upgraded to a heavier, more powerful Pegasus XL model in 1994.

Pegasus consists of three solid-fuel stages with an optional HAPS (Hydrazine Auxiliary Propulsion Stage) monopropellant fourth stage. Alliant Tech Systems (formerly Hercules Aerospace) builds the graphite composite motor case solid fuel stages. Burt Rutan's Scaled Composites, Inc manufactures the graphite composite clipped delta wing and tail surfaces that provide lift and aerodynamic flight control during the vehicle's first stage flight.

Pegasus is drop launched at Mach 0.8 and an alititude of 11.9 km from a modified Lockheed Tristar L-1011 owned by Orbital Sciences named "Stargazer". Pegasus falls for five seconds until its first stage ignites. It then flies a shallow ascent to first stage burn-out, which occurs at a speed of Mach 8.7 and an altitude of 40-65 km, depending on the mission type. The first stage engine has a fixed nozzle. All flight control is provided by the elevator and rudder control surfaces.

The air launch technique reduces total delta-V requirements by 10-15%.

The second and third stages use steerable nozzles to provide pitch and yaw thrust vector control. Roll control is provided by cold gas thrusters. When flown as a three-stage vehicle, the third stage coasts to apogee for several minutes before igniting.

Pegasus suffered teething problems. Five of the first 14 launches performed by the end of 1996 failed. But by the end of 2004, Pegasus had recovered with 21 consecutive successes. By then, Pegasus had flown 35 times from five different launch zones with payloads for commercial, defense, and civil space customers. In addition, three suborbital Pegasus first stages had boosted NASA's Hyper-X hypersonic research test missions.

Pegasus may ultimately fly more often as a traditional, no-wings rocket. Pegasus stages have been combined with Minuteman and Peacekeeper ICBM stages to create Mintotaur and Taurus space launchers. A complete no-wings version of Pegasus, called Orbital Boost Vehicle, has been developed to support missile defense technology development.

Launch Sites

Pegasus is integrated at Vandenberg Air Force Base, then ferried to its launch site by the L-1011 carrier aircraft. Launches have been conducted from Vandenberg, Cape Canaveral, Wallops Island, the Canary Islands, and from Kwajalien in the South Pacific.

NASA's famed B-52 No. 008 "Mother Ship" was used to launch the first dozen or so Pegasus rockets.

Vehicle Configurations

Vehicle Components

References

Pegasus User's Guide, Release 4.0, Oribital Sciences Corp, 1998

Last Update: May 13, 2005