The ParaShield Entry Vehicle Concept: Basic Theory and Flight Test Development

With the emergence of microsatellite launch vehicle technology and the development of interest in space commercialization, there is a renewed need for entry vehicle technology to return mass from low earth orbit. This paper documents the ParaShield concept of the Space Systems Laboratory, which is an ultra-low ballistic coefficient (ULβ) entry vehicle. Trajectory simulations show that as the ballistic coefficient is lowered into the range of 100-150 Pa (2-3lb/ft2) the total heat load and peak heating flux drop markedly due to primary deceleration in regions of extremely low dynamic pressure. In this range any of a number of ceramic or glass-based fabrics can withstand the entry dynamic pressures and heat loads. Incorporating an offset of the center of gravity from the symmetrical axis of the shield allows L/D, and thus peak deceleration loads, to be controlled. By using a titanium support truss and deployment mechanism, a very large heat shield can be deployed from an entry capsule prior to deorbit; since the shield survives entry the same rib-braced fabric structure results in aerodynamic deceleration to a nominal landing velocity of 10-15 m/sec. Thus the same structure that provides heating protection for hypersonic entry is also the terminal decelerator in the subsonic regime and either water splashdown or a mechanical decelerator is used for landing impact attenuation. Since the same structure acts as both the heat shield and the landing parachute, the term "ParaShield" has been adopted to describe this concept Results presented show the application of the ParaShield concept to a variety of entry capsules including advanced manned spacecraft. A test vehicle was prepared to take data on ULβ entry from a suborbital trajectory. This paper also summarizes the experience gained from the design construction, and integration of the Space Systems Laboratory ParaShield test vehicle on the American Rocket Company launch vehicle. With the failure of the launch vehicle, no flight test data was obtained; the test vehicle survived the launch incident, and is flight-capable for future suborbital missions. The development experience summarized in this paper has resulted in a sufficient knowledge base to allow the design and development of orbital ParaShield vehicles.