CONCLUSIONS The power capability of a photovoltaic power system depends greatly on the energy demand placed on the batteries. The available orbital average bus power and system efficiency improves significantly with reduction in nighttime load. Thus, optimization of any photovoltaic/battery system operation in orbit can best be achieved by placing a much larger fraction of the orbital average power demand in the daylight portion of the orbit. This would in effect reduce the actual battery depth of discharge from the original design limit so that an increase in battery life can be expected. If such a day and night load management (DANMOE) strategy is used in sizing solar arrays and batteries, and in the subsequent orbital operations, a large reduction in the specific mass of any photovoltaic power system is possible. This benefit is greater for the LEO than for the GEO application. The DANMOE strategy for both sizing and orbital life extension purposes is feasible, especially on high power spacecraft, if it is properly planned and implemented during the design phase. The DANMOE can be accomplished via ground control. But future spacecraft with an extremely large number of user loads like the Space Station would ultimately need an automated implementation of the DANMOE requirements onboard the spacecraft. A principal drawback of the DANMOE strategy is that a spacecraft, especially low power types may not have sufficient controllable loads and/or loads that can operate mostly or only during the sunlight duration. There are many potential payoffs at the spacecraft level if DANMOE can be utilized. They include extension of satellite lifetime, minimization of spacecraft thermal dissipation management and orbital drag problems (through array area reduction), technology selection options in meeting the spacecraft mass constraints, and cost reduction. REFERENCES 1. M. Savage and Others, "Manned Space Station Relevance to Commercial Telecommunications Satellite: A Prospectus to Year 2000," AIAA/NASA Symposium on the Space Station, Arlington, Virginia, July 18-20, 1983. 2. A. F. Forestieri, "Space Station Solar Array" Proceedings of 4th European Symposium, Photovoltaic Generators in Space, Cannes, France, September 1984. 3. Private Communication with D. Cooper, Intelsat Corp, Washington, DC, August 1985. 4. "MSFC Skylab Electrical Power Systems Mission Evaluation," NASA Technical Memorandum, TMX-64818, NASA Marshall Space Flight Center, June 1974.
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