In this paper, we propose the Gr/Ep mirror without a glass base for solar collector used in a Solar Dynamic Power System, show the optical performance and discuss the durability with regard to the space environment. Design requirements of the solar collector power system are (1) high specular reflectivity, (2) strict dimension tolerance, (3) high stiffness/weight ratio, and (4) durability of materials for the space environment (heating cycle on orbit, atomic oxygen, radioactive rays, etc.). The graphite/epoxy composite structure has a high stiffness/weight ratio and thermal stability. For these reasons, some Gr/Ep collectors have been designed and fabricated. The smoothing surface for reflection cannot be achieved by using only the Gr/Ep structures, so that these collectors usually have a glass base on the Gr/Ep Structure. But using a glass base results in an increase in weight and in unsafety. So we propose utilizing an epoxy resin layer for polishing in place of the above-mentioned glass base. The wavelength of maximum emissive power of solar radiation is 0.5 micron so that the roughness requirement of the solar collector surface is less than 0.05 micron. The usual Gr/Ep composite surface roughness is 0.5-1.0 micron. So we put some additional epoxy resin layer for polishing on the Gr/Ep skins. The resin layer thickness is 0.5-1.0 mm and we get the surface roughness for 0.05 micron smooth enough for a solar collector. We fabricate the flat and spherical mirrors for the measurements of optical performance. The diameter of the spherical mirror is 200 mm and its spherical radius is 1084.5 mm. The surface is coated with aluminum and there is protection film on the aluminum coat. The mirror's specular reflectivity is 0.91 without the protection film and is 0.87 with it by the measurement results of the spectrophotometer and He-Ne laser and the solar power spectrum. The dimensional accuracy of the mirror by the laser reflecting method is less than 1.0 mrad. In addition, the above-mentioned optical results are confirmed through the solar collecting test on the ground. It is thus shown that the proposed mirror becomes the basic structure of a solar collector in respect of optical performance. Durability in the space environment is important and we discuss the heating cycle and the atomic oxygen's attack. The mirror's surface temperature becomes more than 380 K. This fact results in deformation of mirror. But the existence of a thermal radiation film on the mirror surface realizes the low surface temperature, and when the radiation film becomes the protection film against atomic oxygen, the decomposition of the Gr/Ep structure by means of radioactive rays becomes most significant. (Paper number IAF-ICOSP89-4-3.) 4-4. An Experimental Stirling Engine for Solar Space Dynamic Power Designs Kunihisa Eguchi, Sachio Ogiwara & Tsutomu Fujiwara National Aerospace Laboratory, 7-44-1 Jindaiji-Higashi, Chofu, Tokyo, 182 Japan. For the increasing demand for electric power in future space activities, solar dynamic power generation has been viewed as an attractive alternative to conventional photovoltaic and battery systems. Among the thermodynamic cycle engines for solar to electric power conversion, the Stirling cycle with a closed loop of working gas was found to be a more promising candidate through a comparative tradeoff study between heat cycle engines. The present study is intended to design a research model of a free piston Stirling engine generator, named NALSEM-125, and to provide a fundamental understanding of the engine, operation and performance. The NALSEM-125 model is a gamma-type free piston engine/linear alternator unit with a maximum output of 125 W at a design frequency of 30 Hz, in which an electric heater unit is employed as a simulated solar heat source. The displacer piston is crank-linked to an electric motor to evaluate the effect of varying displacer-piston frequency and stroke on overall engine performance. Helium is used as a working fluid. The overall thermal efficiency is 27% at the operating temperature ratio of 2.5, this indicating a 45% of the Carnot efficiency. Since last
RkJQdWJsaXNoZXIy MTU5NjU0Mg==