1. INTRODUCTION: SPACE POWER - UNDERSTANDING THE PROBLEMS Every single spacecraft launched since October 4. 1957 has had no other choice but to carry with it a fully integrated power subsystem able to independently generate, regulate, store and distribute electrical energy. The most widely-used power subsystem involves solar photovoltaic cells in combination with batteries. When the spacecraft is in view of the Sun. the solar arrays provide both electrical power for proper functioning and keep the batteries fully charged. When the spacecraft is in Earth’s shadow, the batteries can be used to maintain the required power without interruption. The only alternative to the solar array/battery combination employed “operationally” is to use the thermal energy given off by the decay of radioactive materials. The US and. to a greater extent, the former USSR are the only nations to have developed nuclear power systems, although Europe used a US-developed Radioisotope Thermoelectric Generator (RTG) to power Ulysses. This situation starkly contrasts with terrestrial activities where most new facilities obtain electrical power supplied remotely from national or international grid systems. A dedicated power station is not built to support each new building, although integral emergency back-up power supply systems are normally installed. On Earth, there are a number of facilities which, like spacecraft, require their own integral power systems. However, these are generally confined to either small-scale activities or remotely located systems (e.g. the Antarctic research base). There are a number of concepts for deploying a “space grid system” in Earth orbit. [1] Simplistically, these concepts generally involve large spacecraft dedicated entirely to providing electrical power to a range of in-space users. Within the context of this study, this is known as the “Powersat” concept
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