Parameters selection of solar thermal rocket engine under flight time limitation
Solar thermal propulsion (STP) is considered as means of inter-orbital transportation from low Earth orbit into geostationary orbit. The payload insertion time for conventional STP usually equals approximately 60days. STP contains high-temperature concentrator-absorber system (CAS) as a power source, with possibility of using multi-staged absorber of non-isothermal type with higher optical-power efficiency. Ballistic efficiency of the upper stage with STP grows with the increase of extent of CAS not-isothermal properties and can exceed1.5-2 times the efficiency of liquid propellant rocket engines (LRE). Ballistic efficiency of upper stage with the STP is determined by relevant parameters of the CAS, to whichwe can assign concentrator accuracy parameter and hydrogen heating temperature in CAS, as well as permissive conditions of CASs sun orientation. Selection of CAS expedient parameters can be realized, in some cases, different from those optimal with allowance for technological limitations under permissible reduction of ballistic efficiency of solar upper stage compared to LRE implementation case. Considering that transportation system, employing combination of high and low thrust engines with adequate insertion time of 60-120 days may compete with STP as inter-orbital transportation system, it is expedient to estimate the ballistic efficiency of solar upper stage at lower flight time. The problem simulation demonstrates the capability of reducing the payload injection time to 20...40 days at high ballistic efficiency of solar upper stage (in case of extreme non-isothermal multi-staged CAS, the payload mass is twice higher compared to LRE). STP optimal relevant parameters herewith change towards CAS simplification. The CAS Sun tracking conditions also become simpler. STP optimal parameter values for various time intervals of inter-orbital transfer are presented. The possibility of providing high ballistic efficiency at the flight time of 20-40 days with STP implementation with non-isothermal multi-staged CAS, compared to the transportation system employing combination of engines of large and low thrust, is shown.