Performance Optimization Analysis Of Solar Thermal Thrusters Under Variable Operating Conditions

Solar thermal propulsion system utilizes a concentrator to gather solar energy for heating propellant to over 2000K,converting internal energy into kinetic energy through the nozzle,and generating thrust.If it takes hydrogen as the propellant,the theoretical specific impulse will be more than 800s.The specific impulse level of the solar thermal propulsion system is between that of the chemical propulsion system and the electric propulsion system.The solar thermal thrusters with adjustable engine thrust gain great performance advantages in space missions such as orbital maneuver and attitude adjustment.This paper focuses on the investigation of the solar thermal thruster by the combination of theoretical analysis,simulation analysis and experimental research.By changing the mass flow of propellant and solar radiation energy,the thrust of solar thermal thruster can be changed.Through theoretical analysis and calculation,the area of 1m~2 concentrator can generate thrust of about 0.4N.To reach the normal operating temperature of the thruster above 2400K,the total concentrator ratio must be at least5000.Eventually,a conclusion can be drawn as changing the flow rate and radiant energy at the same time is more beneficial to the control of thrust.Aiming at the problem that the refraction secondary concentrator is easy to break under high temperature,the regenerative cooling modeling simulation analysis of the condenser and thrust chamber is carried out in this paper.The radiative heat transfer of the absorber was analyzed by coupling of the photothermal and fluid-solid model,and the maximum temperature of the secondary concentrator was found to reduce to 1200K after regenerative cooling,which was lower than the maximum temperature when it was safe to work,and the wall temperature of the absorber remained between 2400K and2600K.The thermal stress analysis of the refraction secondary concentrator(RSC)shows that the difference of the temperatures at each end of the concentrator is considerable,which leads to the thermal stress at the junction between the concentrator and the energy extractor in the middle position to be maximum.With the regenerative cooling method is not adopted,the maximum temperature of RSC has exceeded 2200K,while the RSC temperature drops to 1600K when regenerative cooling is adopted.The simulation model of the heat exchange plate was established and the fluid-solid coupled heat transfer method was used for simulation analysis to obtain the temperature distribution characteristics of the plate and the influence rule of the plate structure parameters on the heating effect.The temperature distribution range of the plate is 1600K～2400K and the heating efficiency is properly good.The influence of the plate structure parameters on the heating effect of heat exchanger is analyzed,and the simulation results show that under the condition of a certain length of flow channel,the cross-sectional area of heat exchanger microchannel should be reduced as much as possible to improve the heating effect,and the heating effect is most favorable when the length of heat exchanger microchannel accounts for about a quarter of the total flow length of the plate.Simulation analysis of the thruster nozzle was carried out to obtain the distribution of ammonia dissociation components under various operating conditions and the system propulsion efficiency and nozzle efficiency when hydrogen was used as working propellant.Based on the research results of the composite and integrated refraction secondary concentrator,heat exchange plate,absorber cavity and nozzle,etc.,the solar thermal thruster variable operating condition experiment was carried out by using the concentrated sunlight of xenon lamp to simulate the concentrated sunlight,which verified the feasibility of regenerative cooling and the feasibility of throttle thrust.