JSUS solar thermal thruster and its integration with thermionic power converter

This paper describes solar heating test results of a single crystal Mo thruster of solar thermal propulsion (STP) with super high-temperature brazing of Mo/Ru for hydrogen-gas sealing, using the paraboloidal concentrator of 1.6 m diameter newly installed in NAL in the Japan Solar Upper Stage (JSUS) research program. The designed thruster has a target Isp about 800 sec for 2,250 K or higher temperatures of hydrogen propellant. Additionally, tungsten CVD-coating was applied to a outer surface of the thruster in order to prevent vaporization of the wall material and Mo/Ru under the condition of high temperature over 2,500K and high vacuum. Also addressed in our paper is solar thermionic power module design for the integration with the STP receiver. The thermionic converter (TIC) module is of a planar type in a Knudsen-mode operation and provides a high conversion efficiency of 23% at the TIC emitter temperature of nearly 1,850 K for a heat input flux of 24 W/cm².