well known that bonding is effective for protecting from charge-up. But it is not sure for large scale structure that there is no problem with bonding. In the design of a large scale solar array, we must pay attention to the direction of the current loop in the solar array. Because the high current loop induces strong magnetic field, we must design the direction of current loop not to influence attitude control of the spacecraft and not to produce Electric Magnetic Interference (EMI) problems. In LEO, high voltage solar array with Direct Current (DC) output collects plasma particles which produces leakage current, ion drag, plasma induced discharge, and contamination caused by sputtering of interconnectors material. These phenomena are dependent upon the array voltage and plasma density. 7.1.2 Solar Dynamic Systems Introduction This section will present an overview of solar dynamic technology as a method for providing power to an orbiting satellite. Solar Dynamic Systems (SDS) work by using a solar concentrator to collect solar radiation and focus it on a receiver to heat up the working fluid. A power conversion unit based usually on either the Brayton, Stirling or Rankine thermodynamic cycles converts the heat energy into electrical energy which then feeds it the satellite. First of all a short summary of the major elements of a solar dynamic system is provided which shows how the system operates. This includes a short description on the thermodynamic cycles. Next the heritage of solar dynamic systems will be discussed. Although there is no known (non-military) solar dynamic system that has been tested in space, there are a number of ground tests that have been performed which help to demonstrate the feasibility of this technology. Finally, future plans for solar dynamic systems will be briefly discussed. This includes the Space Station Freedom SDS which will increase the power generation from 45 kW to 75 kW and the Japanese Space Flyer Unit. Solar Dynamic Systems Elements In this section a review of the main elements of a solar dynamic system will be given. A solar dynamic system (SDS) consists of the following elements: 1. a concentrator used to collect the solar radiator and focus it on a receiver 2. a heat receiver used to convert the solar energy to heat energy and to store energy for eclipse 3. a power conversion unit used to convert the heat energy to electrical energy 4. a heat rejection element used to reject any waste heat to deep space Other elements required include integration hardware to attach the solar dynamic system to the satellite, electrical control equipment, pointing equipment to accurately point the collector at the sun and a power distribution system. Concentrators Concentrators collect solar radiation using a large reflector system and focus it on the receiver. Different designs exist for collector assemblies which make use of standard reflector systems, e.g., Cassegrain or offset Parabolic mirrors with the design chosen depending on the overall system . Figure 7.3 shows examples of four concentrator configurations. The first is a plane receiver with plane reflectors at the edges to reflect additional radiation onto the receiver. The concentration ratio is relatively low with a maximum value of less than 4. The second shows a parabolic reflector which could be a cylindrical surface or a surface of revolution which have much higher concentration ratios. The third shows a Fresnel reflector which uses a set of flat reflectors on a moving array. Alternatively, the facets of the reflector can also be individually mounted and adjusted in position as shown in the fourth example. The concentration ratio, C, is defined as the ratio of the area of aperture Aa to the area of the receiver Ar.
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