Northrop Grumman (Orbital Sciences) ASB-11 Pegasus
Orbital Sciences Corp. and Hercules Aerospace developed the Pegasus winged launch vehicle for small payloads. The vehicle is propelled by three solid fuelled stages and is air-launched by a Tristar launch aircraft, except for the initial six flights which were air-launched from an NB-52B. The Pegasus carries the military designation ASB-11A which probably only applies to military launches.
The basic Pegasus vehicle has a small delta shaped wing with a span of 6.70 m attached to its first stage and the entire vehicle has a length of 15.50 m. The payload bay has a length of 1.83 m and a diameter of 1.22 m. It has a capability to place a 375 kg payload into low-Earth orbit. Some references include the launch aircraft as an additional stage.
| Stage | Length | Diameter | Engine | Fuel | Thrust |
|---|---|---|---|---|---|
| 1 | 8.90 m | 1.22 m | 1 Alliant Techs. Orion 50S | solid | 484,926 N |
| 2 | 2.70 m | 1.22 m | 1 Alliant Techs. Orion 50 | solid | 118,203 N |
| 3 | 2.10 m | 1.22 m | 1 Alliant Techs. Orion 38 | solid | 34,569 N |
Specifications for Pegasus
 |
| Photo: Orbital Sciences |
| Pegasus underneath Stargazer |
The first flight of the Pegasus was on 5 April 1990 and the 10th and last one occurred on 9 October 2000.
The Pegasus XL is an improved version with increased propellant and a length of 17.60 m. It has a capability to place a 443 kg payload into low-Earth orbit.
| Stage | Length | Diameter | Engine | Fuel | Thrust |
|---|---|---|---|---|---|
| 1 | 8.90 m | 1.22 m | 1 Alliant Techs. Orion 50SXL | solid | 589,028 N |
| 2 | 2.70 m | 1.22 m | 1 Alliant Techs. Orion 50XL | solid | 153,508 N |
| 3 | 2.10 m | 1.22 m | 1 Alliant Techs. Orion 38 | solid | 34,569 N |
Specifications for Pegasus XL
 |
| Photo: Author's collection |
| Stargazer launch aircraft |
The first flight of the Pegasus XL was on 9 March 1996, after two failures on 27 June 1994 and 22 June 1995. At the time of this writing, a total of 35 Pegasus XL rockets have flown, the last one on 13 June 2021. One additional Pegasus mission is planned for 2026. Six of the Pegasus XL flights used an additional HAPS (Hydrazine Auxiliary Propulsion System) maneuvering 4th stage. Since 2018, prime contractor for Pegasus is Northrop-Grumman, which had acquired Orbital ATK (merger of Orbital Sciences and Alliant Techsystems) in that year.
At one stage consideration was given to adding two turbojet engines which would assist the vehicle to achieve orbital speed and altitude faster. The two turbojets would have been jettisoned at an altitude of 30 km. This development did not proceed.
Main Sources (for updates in 2026)
[1] Gunter Krebs: Gunter's Space Page (launch lists)
Back to Directory of U.S. Military Rockets and Missiles, Appendix 3
Last Updated: 23 February 2026