SCORPIUS: Solar COncentrating Refrigerated-hydrogen Propulsion for Intelligence with Unfolding Structures

In this proposed effort, RSA will develop a demonstration propulsion system capable of performing multiple high delta-V maneuvers throughout cislunar space, providing increased operational capability to the USSF. RSA’s partner company, Howe Industries, is currently investigating a thermal capacitor for use on smallsats, as shown in Figure 1. To increase the power channeled to the thermal capacitor and reduce the charging time, RSA will develop a large unfoldable reflector that will be coupled to the propulsion system. This large reflector will be able to steer large amounts of solar radiation to the thermal capacitor which then allows for ~3000K of thrust and will be designed to also conduct/intercept communications. The Ruby Sky effort led by RSA is developing a similar optical-grade mirror for use in hypersonic detection and will expand on past research performed at the Marshall Space Flight Center as shown in Figure 2. RSA believes that SCORPIUS would provide high operational value to USSF by providing the same rapid redeployment and long mission endurance of the DRACO program without the risks associated with nuclear power.   The SCORPIUS propulsion system operates by selectively transmitting different wavelengths of light incident from the sun’s solar rays. The infrared light is reflected, and the visible and UV spectra are allowed to pass through the optical system. The thermal capacitor absorbs these wavelengths and raises in temperature. However, it is unable to reject heat in the IR spectrum because of this series of filters and must continue to increase in temperature. In doing so, it melts a phase change material dispersed in the graphite matrix to store energy. Once reaching high temperatures, a working fluid enters the capacitor to extract the heat and propel the spacecraft.   When performing sustained ?V burns the temperature of the core will decrease quickly if a solid thermal capacitor is used, resulting in large performance difference between the beginning of the firing and end of firing. Using a material that can store large amounts of heat and maintain high temperatures is paramount in having an effective warm gas thruster. Thus, the SCORPIUS propulsion system uses a phase change material (PCM) contained within a graphite or tungsten casing. PCMs require latent heat energy to conduct phase changes. This is an ideal solution, as the phase change material sustains a high temperature for a long duration burn. Past work by NASA has investigated suitable materials for a PCM as shown in Table 2 (English 1986). Although the study in question did not extend their research to the high temperatures desired, an initial materials search revealed that both elemental boron and beryllium oxide have melting temperatures above 2500K and a heat of fusion above 2500J/g. This Phase II effort will expand on work previously performed to find an optimal PCM with a high heat of fusion and melting temperature.