Study On Key Problems In The Thermal Control Of Lunar Rover And Selective Adjustment Of Materials' Spectral Properties

Half century has passed since the peak period of lunar exploration developed by both USA and former USSR in 1960s, the science and technology of aerospace is developing so fast that our human being has an urgent requirement for planet exploration. The moon is the nearest natural celestial body, many countries are planning or carrying out the lunar exploration because of its importance in scientific and resources exploitation. The exploration of moon is a key step of our country's space exploration plan, which named as"Chang E Project". The lunar rover plays an important part in lunar exploration after lunching on the lunar surface. But the thermal environment of lunar surface is so bad that it makes huge trouble to the thermal control system design of our lunar rover. Here we design a thermal control and energy system for the lunar rover with taking some key issues into account.The main part of our thermal control system is a structure formed up by MLI materials which can protect the instruments inside the rover stay in a suitable temperature level. Beside the MLI structure, this system contains a reversible radiation cooling surface for heat dissipation, electric heating to live through the lunar night, heat switch and heat pipe to serve the lunar rover. The simulation results of the rover model with MLI structure in lunar night show a good thermal insulation effect from MLI material, this effect can slow down the heat loss speed, as the effective thermal conductivity of MLI material is 1.6×10-4W/m·K, thickness is 5mm, and the emissivity of the cover is 0.8, the heat loss speed is only 4.712W, which means a total energy loss of 1.640kWh in a lunar night. To solve the heat dissipation problem in the lunar daytime, we estimate the main parameters of the heat pipe and the cooling surface.Some experiments were developed to prove the dependability of our simulation with the software of I-DEAS. An environment simulation platform was built to simulate the low temperature and high vacuum features of the lunar night, which means a temperature of 90K and a pressure as low as 10-5Pa. With this platform, we compared the simulation and experiment results, and fabricated one kind of MLI material whose effective thermal conductivity reached 1.456×10-4W/m·K. This parameter made our design exercisable.GaAs solar cell has a much higher efficiency than nuclear cell, while the most advanced lithium ion battery has a much higher specific power than nuclear cell, too. So we evaluated the possibility of using GaAs solar cell and lithium ion battery together as the energy source of the lunar rover. Taking the abundant solar energy resource into account, this energy system can work very well in lunar rover. In the daytime of lunar, the instruments outside the rover body face critical problem of heat dissipation, so we design a device formed up by a radiation cooling surface and heat pipes, with this kind of device these instruments'temperature can be kept below a reasonable level.The observation to the lunar told us the lunar surface is very directional in the reflectivity, so it's inaccuracy to assume the lunar surface as diffused when calculating the exact heat loads from environment. As a solution of this problem, a series of calculation were carried out. From the results, one can see the distribution of the irradiation from the lunar surface onto a square plane. The influence rules of the plane's elevation, azimuth, position and height were researched in detail.The micro fabrication technology has been developing very fast, the fabrication of surface structures in micro or nano scale is quite easy now. With fabricating man-made period micro structures, we can change the thermal radiation properties such as transmissivity, reflectivity and emissivity as designed. In the second part of this paper, the spectral reflectivity in the normal direction of some kinds of silicon period grating has been calculated. Zero-reflection phenomenon has been found in these structures, then one triangle silicon grating was found to perform a strong antireflection ability in some wide bands of infrared.ZnO is an important material in optics and electronics, many kinds of nano structures of ZnO perform different properties in UV-VIS band. Here we constructed a model for some 2-D vertical ZnO nanorod arrays (V-ZNAs) samples with reasonable simplification. In the waveband of 450nm~1500nm, this V-ZNAs structure performs a very low reflectivity and very high transmissivity. So it can be used as good optical couple material and antireflection material with well-selected parameters.