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Orbital Sciences Corporation (OSC) developed the Pegasus launch vehicle to provide their customers the lowest cost per pound to place a 1,000 lb. payload into low Earth orbit. The Pegasus launch vehicle consists of three solid rocket motor stages with a wing and fins for lift and attitude control of the first stage and gimbaled rocket nozzles on the second and third stages. The vehicle is carried aloft horizontally and dropped from a carrier aircraft at approximately 40,000 ft and .8 Mach. Upon motor ignition, the vehicle accelerates to a velocity of 8,300 fps (8.3 Mach) and performs a 2.5 g positive pull up to the correct trajectory angle. The 2nd and 3rd stages are then fired sequentially to place the payload into orbit.

Scaled Composites worked very closely with the OSC personnel from the beginning of the program. Significant flight loads and thermal stresses would have to be supported by the wing and control fins during the launch. Scaled engineering personnel carefully examined the launch profile and developed a composite structure that would meet the OSC performance goals in a cost-effective manner.

The wing structure is primarily graphite/epoxy skins over Rohacell foam cores. An aluminum structural box is used in the center of the wing to accommodate the 4-point carriage loads, which optimizes the structural weight of the wing. Scaled has also performed a block structural upgrade of the wing in order to carry heavier launch loads. The upgrade, called the "XL" uses higher performance IM-8 roving in the spars instead of IM-7, which allowed the upgrade to be accomplished without a change in tooling or schedule. The finished wing weighs approximately 630 LB and will lift, at pull-up, the equivalent weight of a fully loaded Boeing 717 airliner.
Scaled is also responsible for the fabrication and test of the Pegasus tail fins (a graphite/foam sandwich structure over a reinforced urethane core - years before the X-45), the wing-body fairing, and other on-demand special structural components.

All of the Pegasus components are manufactured under a customized quality assurance program which includes full proof loadings before delivery to OSC. The QA program embraces the key principles of Mil-I-45208. The wing and fins contain internal strain gauges and thermocouples to verify performance during proof testing as well as flight loads and temperatures. The data gathered during the launch and flight conditions are used to continually monitor the performance and operating conditions for theses structures. The Scaled-built structures have not had any failures or any modifications after many successful launches.

One example of Scaled's dedicated support for the Pegasus program occurred when the pylon adapter used to fit the Pegasus vehicle to the B-52 launch vehicle failed its qualification inspection. Scaled reviewed the existing structur , conducted a CDR for an all composite pylon adapter two days later and delivered the new pylon adapter, for testing, 14 days after program start. When in production, Scaled builds the Pegasus components at the rate of one shipset per month.



The Pegasus is an air-launched (via a modified Lockheed L-101 I aircraft), three stage, all solid propellant, three axis stabilized vehicle. Manufactured by the Orbital Sciences Corporation, it is the small-class vehicle that DOD will used following the last Scout launch in 1994.

The Pegasus-XL vehicle, a "stretched" version of the original Pegasus vehicle, can place a 400 to 1,000 pound payload into low-Earth orbit.

During a typical flight, the launch aircraft is maneuvered to a predetermined site safely out of range of any populated area. The aircraft climbs to an altitude of 38,000 feet and the Pegasus-XL is released from the belly of the L-101 1. The Pegasus-XL begins an unpowered descent at a rate of approximately 60 feet-per-second while the first-stage arms and prepares for ignition. Forward velocity of Pegasus during the descent is the same as the launch aircraft or Mach 0.8, which is approximately 524 miles per hour. After 5 seconds in free fall, stage-one's solid rocket motor, manufactured by Hercules Aerospace, fires and burns for approximately 71 seconds. The Pegasus 22 foot, delta-shaped wing begins to produce lift as the Pegasus accelerates, and the launch vehicle begins a 2.5 g-force pull-up. As Pegasus climbs, the booster experiences maximum dynamic pressure (Max-q) of approximately 1,200 pounds per square foot approximately 30 seconds after first-stage ignition. (For comparison, on a typical space shuttle launch, Max-q is equal to approximately 600-700 pounds per square foot.)

The second stage Hercules solid fuel motor ignites about I minute 35 seconds into the flight at an altitude of 37 miles and at approximately 2 minutes, the payload fairing is ejected. The second stage flies to an altitude of approximately l29 miles with a velocity of over 12,000 miles per hour. At the appropriate altitude to achieve the designated orbit, the third stage Hercules motor ignites and burns for 1 minute and 6 seconds to place its payload into orbit.

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.

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.

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.

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.

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).

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.

On April 5, 1990, Orbital began a new era in commercial space flight when our Pegasus rocket was launched for the first time from beneath a NASA B-52 carrier aircraft in a mission that originated from Dryden Flight Research Center in California. In the decade since its maiden flight, Pegasus has become the world's standard for affordable and reliable small launch vehicles. It has conducted 37 missions, launching more than 78 satellites.

The three-stage Pegasus is used by commercial, government and international customers to deploy small satellites weighing up to 1,000 pounds into low-Earth orbit. Pegasus is carried aloft by our "Stargazer" L-1011 aircraft to approximately 40,000 feet over open ocean, where it is released and then free-falls in a horizontal position for five seconds before igniting its first stage rocket motor. With the aerodynamic lift generated by its unique delta-shaped wing, Pegasus typically delivers satellites into orbit in a little over 10 minutes.

This patented air-launch system reduces cost and provides customers with unparalleled flexibility to operate from virtually anywhere on Earth with minimal ground support requirements. Pegasus launches have been conducted from six separate sites in the U.S., Europe and the Marshall Islands, the first time a space launch vehicle has demonstrated such operational flexibility.


Orbital Sciences Corporation developed the Pegasus launch vehicle to provide their customers the lowest cost per pound to place a 1,000 LB payload into low Earth orbit. The Pegasus launch vehicle consists of three solid rocket motor stages with a wing and fins for lift and attitude control of the first stage and gimbaled rocket nozzles on the second and third stages.

Scaled Composites engineering personnel carefully examined the launch profile and developed a composite structure that would meet the OSC performance goals in a cost-effective manner. Scaled Composites is also responsible for the fabrication and test of the Pegasus tail fins.

The NB-52B became the world's first manned, winged, return to launch site satellite launcher when it launched the Orbital Sciences' Pegasus booster on April 5, 1990. The NB-52B was displayed with Pegasus s/n 002 at the October 6, 1990 Edwards Air Force Base Open House. Pegasus s/n 002 was launched with seven 48-pound Microsats on July 17, 1991. A failure during the first stage separation resulted in the satellites failing to achive the proper orbits. The last Pegasus launch from the NB-52B took place on August 3, 1994.

A Pegasus-XL rocket was launched from Stargazer, the Orbital Sciences L-1011, at 6:56 P.M. on March 4, 1999. Its payload was the Wide-field Infra Red Explorer (WIRE) satellite. The booster climbed out of the earth's shadow during the second stage engine burn in this time exposure. It is framed by the planets Mercury, Jupiter, Venus, and Saturn. The bright spot at the lower right is the lights of the town of Buellton in the Santa Ynez Valley.


Currently, the Kern County Air Terminal at Meadows Field just north of Bakersfield along Hwy 99 is the roosting spot for a specially modified Lockheed L-1011 jumbo jet owned and operated by Dulles, VA-based Orbital Sciences Corporation. Called "Stargazer," the aircraft is used as the airborne launch platform for the PegasusXL and X-34 technology testbed demonstrator spacecraft.


Washington DC (SPX) Oct 28, 2004
NASA announced Thursday is the next launch attempt for the Demonstration of Autonomous Rendezvous Technology (DART) spacecraft. The launch window opens at 2:16:13 p.m. EDT and closes at 2:21:57 p.m. EDT.

The launch is from Vandenberg Air Force Base, Calif. aboard an Orbital Sciences Corp. Pegasus XL vehicle. The target drop time of the Pegasus from the carrier aircraft is 2:18 p.m. EDT.

The DART spacecraft will be launched on the Pegasus vehicle from its Stargazer L-1011 jet aircraft. At approximately 40,000 feet over the Pacific Ocean, the Pegasus will be released with the DART spacecraft.


Pegasus "Firsts"

* World's first privately developed space launch vehicle
* Maiden 1990 mission marked the first all-new, unmanned space launch vehicle developed in the U.S. in more than 20 years
* First winged vehicle to accelerate to eight times the speed of sound
* First air-launched rocket to place satellites into orbit, using its carrier aircraft as an "air breathing reusable first stage"



Crew/passengers: none

Main sources:
- Space Launch Report
- SpaceDaily