Development of a Modular Solar Thermal Propulsion Engine

A new modular solar powered rocket engine is proposed to provide a few milligrams to a few kilograms of thrust at 1100-1600 seconds of specific impulse by heating hydrogen propellant to average temperatures ranging from 2750 to 3250K. The proposed design utilizes one or several sunflower-like clusters of non-imaging concentrators coupled to optical fiber bundles that guide the solar energy with a throughput of greater than 80% into a Plank cavity/thrust chamber. The Plank cavity receives and entraps solar energy for direct heating of hydrogen and/or storage in a composite thermal storage unit. A nested flow path is designed to force hydrogen flow along the thermal storage/cavity temperature gradient, thereby, producing variable levels of thrust at relatively constant specific impulse of 1100 to 1600 seconds. This is a revolutionary improvement over existing solar-electric powered space propulsion systems and could lead to the development of an ultra-light, compact, and an order of magnitude lower cost propulsion system for space transportation and solar system exploration. Phase I results have demonstrated the feasibility of a low-pressure fed, high temperature solar thermal propulsion system for achieving high Isp. Also, demonstrated in Phase I was the ability to coat graphite for the thermal storage unit with refractory metal carbides to protect from the flowing hot hydrogen propellant.