Phase-Change Thermal Energy Storage and Conversion: Development and Analysis for Solar Thermal Propulsion

Abstract

Solar thermal propulsion offers a unique combination of high thrust and high specific impulse that can provide competitive advantages relative to traditional satellite propulsion systems. Enhancing the functionality of this technology will require a robust thermal energy storage method that can be combined with a means of thermal-to-electric conversion (i.e. thermophotovoltaic cells). This combination creates a high performance dual mode power and propulsion system that can eliminate the traditional photovoltaic-battery combination on existing satellites. A thermal energy storage system based on the phase change of molten elemental materials is proposed as the enabling technology. Molten boron is identified as the optimal phase change material (PCM), but presents significant engineering challenges. Thus, molten silicon is proposed as a near term, moderate performance storage option. A systems level comparison against existing technologies shows that both thermal storage materials present a performance benefit versus current technological benchmarks, and with optimistic future assumptions, it appears that a boron-based system can provide a ∆V improvement of more than 40% while maintaining rapid satellite maneuverability. An ongoing experimental effort is focused on producing a proof of concept thermal energy storage system. Materials testing has determined the stability of boron nitride in the presence of molten silicon in the short term, and solar furnace testing has resulted in silicon melting for the first time. Testing of the solar furnace using copper as a surrogate PCM has revealed experimental concerns with PCM heat transfer rates and has resulted in a design for a new full scale solar furnace. This furnace will operate at scales that are relevant to spacecraft development.

Experimental Investigation of Latent Heat Thermal Energy Storage for Bi-Modal Solar Thermal Propulsion

“…The performance of the proposed bi-modal system has been evaluated and has been shown to be advantageous potentially providing up to 60% more ∆V than a similarly sized monopropellant chemical system when using an advanced boron-based configuration. 5 Unlike previous STP development efforts targeting large scale spacecraft, the microsatellite platform amplifies the benefits of an STP system. The proposed scale is below the range of bi-propellant systems and is unable to generate sufficient electrical power for high thrust electric propulsion.…”

“…The particular application explored here is that of a microsatellite combined power and propulsion system. The design goals of such a system have been discussed previously, [2][3][4][5] and will only be briefly recapitulated here.…”

“…4 Additional technological requirements such as advanced insulation and high performance thermal electric conversion also appear to have readily applicable solutions which can be drawn from previous research efforts. 5,6 The remaining technological challenge for a bi-modal STP system is high performance thermal energy storage. Previous solar thermal efforts have included sensible heat thermal energy storage in their design by using high temperature materials such as graphite and boron carbide.…”

“…To mitigate these issues, it has been suggested that a solar thermal propulsion system be combined with high performance thermal energy storage (to eliminate any timing constraints on propulsive maneuvers) and a means of thermal-electric conversion (to eliminate the need for a 'legacy' power system) in a bi-modal configuration. [2][3][4][5][6] With such a combined system, solar thermal energy could provide both propulsive and electrical power for a satellite. A technological review has indicated that effective thermal energy storage is the enabling technology for such a system and it is proposed that the latent heat of molten elemental materials can provide a robust, high temperature, and high density thermal energy storage solution.…”

Optimum semiconductor bandgaps in single junction and multijunction thermophotovoltaic converters

“…The above characteristics combined with the many different possible sources of heat led to a broad range of applications for TPV technology, including heat recovery from high temperature industrial processes [4][5][6], combined heat and power for residential use [7][8][9][10][11], solar power [3,[12][13][14][15][16][17][18], portable energy sources [8,[19][20][21], space power [22][23][24][25][26], energy storage systems [16,[25][26][27], among others.…”