Flight efficiency of solar thermal propulsion with double-stage thermal energy storage

The activity urgency is connected with requirement of heavy spacecraft ascent into high working orbits. The solar thermal propulsion (STP) with double-stage latent heat thermal energy storage (TES) is intended for space vehicle delivery into geostationary orbit (GEO). Double-stage TES contains peripheral stage as “solar concentrator – sunlight absorber-thermal energy storage” system (CATS) with relatively low-temperature heat-accumulating phase-changing material (HAM) having high latent heat of fusion, for instance, lithium hydride, and high-temperature central stage with high power-intensive TES, for example, beryllium oxide, that allows obtaining of high specific impulse 900 sec. Inter-orbital transfer time from low earth orbit (LEO)-to-GEO varies from 20 to 90 days. Expedient optical-energetic characteristic parameters of the STP for each flight time shows that expedient accuracy of the solar mirror concentrator is much less in comparison with single-stage CATS with beryllium oxide as the HAM, therefore the CATS Sun tracking conditions can be significantly simplified. Comparison between the STP and alternative means of inter-orbital transportation shows that payload mass on GEO seriously exceeds that for liquid propulsion or combined upper stages with both chemical and electric propulsion. Use of the STP with heated hydrogen after-burning allows payload mass increasing at relatively low transfer time, as well as reduction of space vehicle dimensions and the CATS complication. The expedient oxidizer-to-fuel mass ratios depend on LEO-to-GEO trip time. The considered possible variants of payloads – geostationary communication satellites – can be injected into the target orbit with use of “Soyuz-2.1b” middle class launchers having the “solar” upper stage instead of “Proton-M” heavy rockets class with chemical liquid-propellant kick-stages.