The choice of heat-accumulating materials for solar thermal propulsion

Solar thermal propulsion (STP) with thermal energy storage (TES) using high-temperature heat-accumulating materials (HAM) with high specific heat of fusion is considered. These HAM possess power advantages over solid-state graphitic accumulators. TES is structurally combined with “concentrator-absorber” system (CAS) and is intended to accumulation of thermal energy from the mirror-image solar concentrator during the periods of space vehicle motion at passive legs of multi-burn trajectory. Firings of the STP are realized at apsidal areas of the transfer orbits at the expense of the thermal discharge of the TES, heating the propulsive mass (hydrogen) up to high temperatures and providing high specific impulse. Independence of processes of precise orientation of the CAS to the Sun during the periods of passive motion of the space vehicle for charge of TES, and thrust vector control is thus provided at accumulator discharge at active legs of the trajectory. Areas of firings of the STP thus do not depend on illuminance conditions. Such refractory HAM as beryllium oxide and binary eutectic B*Si and 3BeO*2MgO with fusion temperature above 2000 K and specific heat of fusion higher than 2 MJ/kg are considered. The problem of inter-orbital transfer of space vehicle from LEO to GEO within 60 days is observed. Payload mass as a criterion of efficiency flight is maximized by optimization of relevant parameters of CAS and TES. It is possible to consider such relevant parameters as the ratio of masses of the concentrator and the TES and parameter of accuracy of the pseudo-paraboloid concentrator. Joint optimization of relevant parameters is conducted. Their expedient values for each of the considered HAM are shown. It is shown that at use of B*Si alloy the payload mass can be higher in comparison with other considered materials. The CAS tracking conditions to the Sun thus corresponds enough to modern technical feasibilities. The gain in payload mass can exceeds 1.5 times of efficiency of launchers with the state-of-the-art upper stages, and allows to use of smaller class launchers.