(U) Pegasus

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)

Overview: (U)
(U) The Pegasus/Pegasus XL program was initiated as a joint Air Force and industry venture in 1987.  The Pegasus launches small, mainly experimental Air Force payloads into Low Earth Orbit (LEO).  The manufacturer, Orbital (aka, Orbital Sciences Corporation), used a small team to design and build a flight-ready vehicle in three years. The first successful launch of the Pegasus from the wing of a NASA B-52 originated at Edwards AFB and took place off the coast of California on 15 Apr 90. The Pegasus was lengthened to its current configuration and won the competition for the Air Force Small Launch Vehicle (AFSLV) contract.  There have been a total of seventeen Pegasus launches of all types to date (10 of the Pegasus XL stretched version were launched from Orbital's L-1011 carrier aircraft).  The majority of the launches have been from Vandenberg AFB, California, but Wallops Island, VA, Kennedy Space Center, and Gondo AB on Gran Canaria Island, Spain have also supported Pegasus operations. 

(U) A unique feature of the Pegasus is that it is the only existing space booster that is launched from beneath an airborne platform. Pegasus does not require a ground launch platform, just a runway from which the carrier aircraft can take-off and land. The carrier aircraft serves as the first booster stage, which reduces the amount of propellant the vehicle requires. Initially, a NASA B-52 was used to launch the Pegasus; now, a specially modified L-1011 serves as the launch platform.

Description: (U)
(U) Pegasus is a three stage, solid propellant, inertially guided, composite winged space booster.  It is air launched after being carried by an L-1011 aircraft to approximately 40,000 ft altitude and Mach 0.8 airspeed.  There are two versions of the Pegasus, the Standard model and the XL (Extended Length).  The Standard Pegasus is 50 feet long, 50 inches in diameter and weighs 41,000 gross pound.  The XL is 55 feet long and weighs 50,000 gross pounds. The Standard and the XL have the same basic configuration. The vehicle has a blunt payload fairing, which blends into a cylindrical fuselage and ends in a flared exhaust nozzle. The cylindrical fuselage is divided into three stages. Each stage is a motor case made of a graphite-fiber, epoxy-matrix composite and each case is filled with solid hydroxyl terminated polybutadiene (HTPB) class 1.3 propellant.  The Standard Pegasus produces over 140,000 lbs of thrust, and the XL produces over 200,000 lbs of thrust. 

(U) A large, triangular wing mounted atop the first stage provides lift while the vehicle is still in the atmosphere. The wing is composed of composite material and has a span of 22 ft.  An aerodynamic fillet provides a clean transition between the wing and the fuselage.  There are three electromechanically-actuated control fins mounted on the aft end of the fuselage. These provide pitch, roll and yaw control for the vehicle while it is still in the atmosphere.  Small rockets mounted in the base of each fin augment the control authority when the vehicle reaches the upper atmosphere.  After first stage separation, pitch and yaw control is maintained through thrust vectoring of the second and third stage rocket nozzles. Roll control is provided through a nitrogen cold-gas reaction control system.  The Pegasus is capable of placing 1,000 lb payloads into Equatorial orbits; 750 lb payload into Polar and Sun-synchronous orbits; 400 lb payloads to Geosynchronous Transfer Orbits; and payloads up to 300 lb to Earth escape velocity. 

(U) Pegasus reduces launch costs by decreasing the time required for vehicle processing. Current mission timelines project a motor receipt to launch processing time of 65 days. This is in contrast to 120 + days for other launch systems.  The program has demonstrated back-to-back Pegasus launches in under 30 days (NASA SeaStar to USAF FORTE in 29 days).

User Impact: (U)
(U)  The Pegasus Program provides commercial and government space users with an effective, low-cost means of launching small payloads into LEO.  It offers potential users operational flexibility and reliability.

Programmatics: (U)
(U) Operational.

Related Initiatives: (U)
(U) MSTI, Rocket System Launch Program

Related Requirements: (U)
(U) None.

Related Categories: (U)
(U) Launch Vehicles, Spacelift

Road Map Placements: (U)
(U) SPACE FORCES SUPPORT.

Lead Office: (U)
(U) Air Force.

Date of Information: (U)
29 October 1997

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)