A Status Report of the X-50LR Program - A Laser Propulsion Program

Abstract

Abstract : In 1996, the Air Force Research Lab's Propulsion Division at Edwards AFB initiated a program that had as its main objective to launch a laser-propelled vehicle into a suborbital trajectory within a period of 5 years in order to demonstrate the concept and its attractive features. The concept was to be a nanosatellite in which the laser propulsion engine and satellite hardware were intimately shared. This concept was based upon a 1989 design developed at Rensselaer Polytechnic Institute under a Space Defense Initiative Office laser propulsion program. The forebody aeroshell had been designed to act as an external compression surface (i.e. the airbreathing engine inlet). The afterbody served a dual function as a primary receptive optic (parabolic mirror) for the laser beam and as an external expansion surface (plug nozzle). The primary thrust structure was the centrally located annular shroud. The shroud provided air through inlets and acts as a energy absorption chamber for plasma formation. In the rocket mode, the air inlets were closed, and the afterbody and shroud combined to form the rocket thrust chamber and plug (aerospike-type) nozzle. The fully-scale vehicle was 1.4 meters in diameter with a dry mass of 120 kg. Fully fueled, this vehicle would have an initial mass of about 240 kg (i.e., a mass fraction of 0.5), and would be launched into orbit with a 100 megawatt-class infrared ground-based laser(GBL). This laser propelled vehicle would be a single-stage-to-orbit (i.e., airbreathing only to M=5 and 30 km; a laser thermal rocket, using liquid propellants, at higher altitudes and in space) using a combined-cycle pulsed detonation engine. Once in space, the Lightcraft was to use its one meter diameter optical system to provide, for example, Earth surveys from low Earth orbit with 8-15 cm resolution in the visible light frequencies. Such a device was simple, reliable, safe, environmentally clean, and could have a very high all azimuth on demand launch rate.7