Spectral-Selective Solar Thermal Micro-Thruster

Abstract

(Abstract) The paper deals with continuation of study of the problem of solar thermal propulsion efficiency increase. Spectral-selective coatings for absorber-thruster system permitting significant are considered Use of the considered types of CAS strongly simplifies Sun tracking conditions and ensures more effective heating compared to conventional STP concepts. In the last papers the authors have shown theoretically that increasing temperature raises parameter of selectivity highly depending on maximum possible concentration ratio of sunlight. Therefore it is possible to obtain better spectral-selective properties at high temperatures. Such high-temperature spectral-selective coatings will be able to raise CAS optical-energetic efficiency and significantly simplify the Sun tracking conditions for different orientation modes. For the advanced small upper stages with micro/nano-satellites, being developed by the leading space companies, it is extremely important to economy a propellant mass for prolonged oriented space flight due to limitation of on-board propellant tank volume. Therefore there is rather urgent question to increase specific impulse for on-board orbital maneuvering system (OMS) or reaction control systems (RCS). It is very important for micro-propulsion systems (PS) especially based on the MEMS technologies due to the scale factor and, hence, due to high level of specific impulse losses. However, for conventional liquid or stored-gas PS the possibilities for further increase of specific impulse are strongly restricted. Therefore it is expedient to use propellants with increased enthalpy, particularly, propellants heated by concentrated solar energy. Specific impulse of solar thermal propulsion (STP) can be sharply (1.5-2 times) increased. STP is expected also to offer improved operability by avoiding toxic of environmentally hazardous propellants. There are some critical problems for conventional PS: 1. Low Specific Impulse for Stored-Gas System and Mono-Propellant RCS (70-220 sec) 2. Low Total Impulse (5'000 lb*sec for Stored-Gas and up to 50'000 lb*sec for Liquid-Propellant RCS)