Pegasus: A Geosynchronous Launch Profile

Pegasus is a low cost system which can carry a 600 pound payload to 250 nautical mile polar orbits as well as larger payloads to lower altitude/ lower inclination orbits or suborbital trajectories. The craft is carried aloft by a conventional transport/bomber-class aircraft and launched from level flight at approximately 40,000 ft. The first flight of Pegasus was made on April 5, 1990 over the Western Test Range at an altitude of 43,000 feet using the NASA B-52. The unmanned launch vehicle was developed jointly by Orbital Science Corporation (OSC) and Hercules Aerospace Company and the first flight which reached a 320 nmi orbit was conducted by, DARPA (Defense Advanced Research Projects Agency) and NASA's Goddard Space Flight Center. The Pegasus launcher is 49.2 feet in length, has a diameter of 50 inches and a gross weight of 41,000 pounds. The payload can have a length up to 72 inches and a diameter of 46 inches. A 3-axis, gravity gradient or spin-stabilized spacecraft can be achieved or a number of small satellites can be inserted. A preliminary propulsion design analysis for the launching of a small geosynchronous Earth satellite aboard Pegasus was performed. The problem for the positioning of the satellite is presented with emphasis on the effects of orbital parameters such as the Low-Earth Orbit (LEO) altitude, propellant, and launch site latitude on the spacecraft's propellant budget and beginning of life (BOL) mass. A comparison of conventional launch vehicles and the Pegasus launch vehicle is also presented. A Pegasus fourth stage was sized based on the propellant mass required for geosynchronous orbit (GEO) injection. Recommendations for a launch profile were made based upon minimizing the propellant used in the apogee boost motor (ABM) and perigee boost motor (PBH) or fourth stage used to place a small satellite into geosynchronous orbit.