Solar thermal propulsion with different types of concentrator-absorber system

Solar thermal propulsion (STP) with high-temperature concentrator-absorber system (CAS), as a power source, is observed. Ordinary observed STP with simple single-stage isothermal absorber-heat exchanger, executed as an absolute black body, requires high accuracy of reflecting surface of solar mirror-image concentrator and high-precision tracking conditions to the Sun on active legs of multi-burn injection trajectory. Reduction of these requirements is possible at use of CAS with organization of non-uniform heating of hydrogen in absorber which temperature corresponds to exponential law of distribution of radiant flux density in focal sunlight spot. Energetic efficiency of such CAS is higher in comparison with the isothermal one. Single-stage, double-stage and extreme-not isothermal (multi-stage) CAS are considered. Results of simulation of STP with the considered CAS for upper stage application in mission of non-coplanar payload transfer from LEO to GEO are shown. It is shown that ballistic efficiency of solar upper stage with the considered STP can more than twice exceeds capabilities of modern liquid-propellant upper stages. Comparison of ballistic efficiency of STP use with different CAS as means of inter-orbital transportation is carried out. It is shown that the efficiency rises with increase of ratio of non-uniformity of hydrogen heating in sunlight absorber-heat exchanger and can be 30 % higher as compared to ordinary STP use. Such relevant CAS parameters as accuracy parameter of mirror-image concentrator and hydrogen heating temperature in the absorber-heat exchanger are considered. Optimal relevant parameters for criterion of maximum of payload mass for the considered CAS types are determined, and recommendations for their choice with technological restrictions are suggested. Dimensional parameters of concentrators for the cases of isothermal and staged absorbers are shown. Conditions of orientation to the Sun for the different CAS are observed. It is shown that requirements to the Sun tracking system in dynamic orientation mode can be quite provided by modern hardware components, especially in the case of non-uniform heating of hydrogen.