Copyright© 1997, American Institute of Aeronautics and Astronautics, Inc. A Pneumatic Approach to First Stage Acceleration for Highly Reusable Space Transportation Systems M. R. Brown*, M. Frank Rose t ,and R. M. Jenkins* Auburn University, AL A. J. Juhasz" NASA Lewis Research Center Abstract This paper describes the results of a ballistic analysis of the characteristics of a pneumatic first-stage launch system which could accelerate a vehicle/payload of specified size and mass to a desired final velocity within specified acceleration constraints. The constraints chosen for the study are (1) 65 metric ton vehicle mass, (2) -270 m/s (880 fps) velocity, and (3) constant 3-g acceleration profile. The ballistic problem is one of determining the required vehicle base pressure distribution as a function of residence time (distance) in the launch tube through solution of the vehicle equation of motion. The vehicle aerodynamic drag may be either internal (sabot configuration) or a combination of internal and external drag (catapult configuration). In certain instances utilizing a sabot, the launch tube may be evacuated, so that aerodynamic drag is negligible. Nomenclature Atasc * projectile (rear) projected area C D * external vehicle drag (catapult only) C f * launch tube skin friction coefficient dV(tydt m projectile acceleration (sabot) seal drag ag ~ projectile aerodynamic drag g - acceleration due to gravity k m ratio of specific heats ^Graduate Research Assistant, Aerospace Engineering fDirector, Space Power Institute & Professor, Electrical Engineering 'Associate Professor, Aerospace Engineering "Senior Project Engineer & Consultant, Power Technology Division Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved m - projectile mass M m flow Mach number M 0 • projectile Mach number P - static pressure P 0 - stagnation pressure Phase " projectile base pressure Re - Reynolds number t " time *KWK/ • time required for initial compression wave to reach the launch tube exit tfiui * t ' me required for projectile to reach the launch tube exit <p « projectile launch angle (zero = horizontal) Introduction The Highly Reusable Space Transportation (HRST) program has placed considerable emphasis on the development of unconventional first stage launch technologies which could accelerate a vehicle/payload to a velocity of approximately 200 - 270 m/s. Such launch assist technologies could provide a high- leverage performance factor for propellant mass fraction and Isp through reduced AV requirements for the main propulsion system. Pertinent technologies include air launch (e.g., Pegasus), magnetic levitation, and pneumatic launch. As pointed out in a preliminary survey of relevant electrical technologies by Merryman , a pneumatic or light gas gun approach to such a first stage could provide a relatively simple, inexpensive, and robust launch system. First stage acceleration would then be treated basically as an internal ballistics problem of the type found in hypervelocity light gas guns and pneumatic tubes such as those found on submarines for launch of ballistic missiles and torpedoes. The approach taken in the present study is that the internal flows (fore and aft of the vehicle) are one dimensional and quasi-steady in Downloaded by PURDUE UNIVERSITY on June 27, 2016 | http://arc.aiaa.org | DOI: 10.2514/6.1997-3212