Pegasus rocket
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Pegasus_rocket.jpg
PegasusXL.jpg
The Pegasus rocket is a winged space booster developed by Orbital Sciences Corporation (OSC). Three main stages, filled with solid propellant, provide most thrust. A fourth stage, fueled with hydrazine, can be added. The vehicle is launched from another aircraft at approximately 40,000 feet. Initially, this was a B-52. But OSC soon transitioned to their "Stargazer" L-1011, a retired airliner. The vehicle is capable of placing small payloads into low altitude orbits. The first successful Pegasus launch occurred on April 5 1990. A Pegasus XL, with lengthened stages, provides increased payload.
- Mass: 18,500 kg (Pegasus), 23,130 kg (Pegasus XL)
- Length: 16.9 m (Pegasus), 17.6 m (Pegasus XL)
- Diameter: 1.27 m
- Wing Span: 6.7 m
- Payload: 443 kg
The Pegasus's three Orion solid motors were originally developed for the cancelled Midgetman, a small ICBM to be launched from a trailer. For Pegasus use, wing and tail assemblies and a payload fairing were developed. The 45-degree delta wing was designed by Burt Rutan. The tail fins provide steering for first-stage flight, as the Orion 50S motors do not have thrust-vectoring nozzles. The fairing has a 1.2m usable diameter.
In a Pegasus launch, the carrier aircraft takes off from a runway with support and checkout facilities. Such locations have included Kennedy Space Center, Florida; Vandenberg Air Force Base, California; Wallops Flight Facility, Virginia; Kwajalein Range in the Pacific Ocean, and the Canary Islands in the Atlantic.
Upon reaching a predetermined staging location and altitude, the aircraft releases the Pegasus. After five seconds of free-fall, the first stage ignites and the vehicle pitches up. Approximately 1 minute and 17 seconds later, the Orion 50S motor burns out. The first stage falls away, taking the wing and tail surfaces, and the second stage ignites for approximately 1 minute and 18 seconds. Attitude control is by thrust vectoring the Orion 50 motor in two directions; roll is provided by nitrogen thrusters on the third stage.
Midway through second-stage flight, the launcher has reached a near-vacuum altitude. The fairing splits and falls away, uncovering the payload and third stage. Upon burnout of the second stage's motor, the stack coasts until reaching a suitable point in its trajectory, depending on mission. Then the third stage's Orion 38 motor ignites. It too has a thrust-vectoring nozzle. After approximately 64 seconds, the third stage burns out. A fourth stage is sometimes added for a higher altitude, finer altitude accuracy, or more complex maneuvers. The HAPS (Hydrazine Auxiliary Propulsion System) is powered by three restartable, monopropellant hydrazine thrusters.
In the Pegasus XL, introduced in 1994, the first two stages are lengthened into the Orion 50SXL and Orion 50XL. Higher stages are unchanged; flight operations are similar. The standard Pegasus has been discontinued.
Pegasus components have also been the basis of other OSC launchers. The ground-launched Taurus rocket places the Orion 50 and 38 stages atop a Castor 120 first stage, derived from the first stage of the MX ("Peacekeeper") missile. The initial launches used refurbished MX first stages.
The Minotaur, also ground-launched, is a combination of stages from Taurus launchers and Minuteman missiles. The first two stages are from a Minuteman II; the upper stages are Orion 50XL and 38.
External links
- Encyclopedia Astronautica entry (http://www.astronautix.com/lvs/pegasus.htm)
- Orbital Sciences Corporation page (http://www.orbital.com/)
- Pegasus Rocket page (http://www.orbital.com/SpaceLaunch/Pegasus/index.html)
- Pegasus Mission History (http://www.orbital.com/SpaceLaunch/Pegasus/pegasus_history.htm)de:Pegasus (Rakete)