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The Pegasus is an air-launched (via a modified Lockheed L-1011 aircraft), three stage, all solid propellant, three axis stabilized vehicle. Manufactured by the Orbital Sciences Corporation, it was the small-class vehicle that DOD 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. The original, or standard, version of the Pegasus was retired in 2000, after which only the Pegasus XL was used.

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-1011. 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.

NASA certified Pegasus to carry the highest value satellites (Category Three Certification) because of its excellent demonstrated reliability record. Pegasus has launched its last 21 missions successfully. No Pegasus XL vehicles flew in 2004. Two Pegasus XL missions were scheduled for 2005, carry-ing the Demonstration of Autonomous Rendezvous Technology (DART) flight demonstrator vehicle for NASA and the Communication/Navigation Outage Forecasting System (C/NOFS), a USAF payload whose launch will be licensed by FAA/AST.

Orbital ATK’s winged Pegasus XL rocket flew 15 December 2016 from the Cape for the first time in 13 years, launching far out over the Atlantic Ocean, after being dropped from a carrier aircraft at nearly 40,000 feet. The 57-foot, 50,000-pound Pegasus delivered NASA’s $157 million Cyclone Global Navigation Satellite System mission, or CYGNSS, to low Earth orbit. The eight microsatellite observatories of the CYGNSS spacecraft have been deployed into orbit following launch aboard the Orbital ATK Pegasus XL rocket.

The Ionospheric Connection Explorer (ICON) observatory will orbit Earth to explore its ionosphere. The project planned to complete system-level integration and testing in April 2017 and ship the spacecraft for launch by May 2017. The project moved its planned launch date from June to July 2017 due to a delay in the delivery of two of the three segments of the Pegasus launch vehicle.

Stratolaunch, founded in 2011 by Paul G. Allen, is developing an air-launch platform to make access to space more convenient, reliable, and routine. Stratolaunch Systems will use the giant aircraft the company is currently developing to launch Pegasus rockets from Orbital ATK as part of a “multi-year” partnership, the two companies announced 06 October 2016.

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