The growth of power requirements to this level has led to mass and reliability of the power system - strongly dependent on its architecture - becoming key factors in system design optimization and in manufacturing costs. A summary of European spacecraft power requirements is discussed in the following section. 3.1 Power System Requirements 3.1.1 Power System Requirements for LEO Missions The power system designs for photovoltaic based LEO missions are characterized by large dynamic energy flows between the solar array, energy storage devices, and the main bus distribution system. This behavior is often compounded by the need for high payload power levels for Earth monitoring or microgravity science. The detailed design of such a power system represents a significant engineering challenge. ESA is currently directing a number of LEO flight programmes. These include the STS launched European Retrievable Carrier (EURECA), the Earth Resources Satellite (ERS-1) and the three COLUMBUS elements - the attached laboratorymodule for Space Station FREEDOM, the free flying laboratory module, and the polar orbiting platform. All of these missions are three axis stabilized. The detailed design definition phase of the HERMES program has begun, again increasing projected demands on power system technology. The power system for the manned orbital system is also under study at this time. 3.1.1.1 EURECA The EURECA power system supplies about 2.6 kilowatts to the payload continuously. The payload consists of microgravity experiments and technology demonstration packages for interorbital communications and ion propulsion. In the EURECA power system individual sections of the 5 kilowatt solar array are connected either to the spacecraft batteries, or directly to the 28 volt regulated main power bus. This 'hybrid' architecture results in a fairly simple method for recharging the four thirty cell, forty ampere hour nickel-cadmium batteries, yet maintains the efficiency and performance advantages of a fully regulated power bus. Since the battery voltages always exceed that of the bus in this design, the battery discharge regulators utilize the simple and effective 'buck' topology. This design yields measured efficiencies exceeding 94% for the 2.6 kilowatt, 28 volt design conditions. 3.1.1.2 ERS-1 The ERS-1 spacecraft power system takes a centralized approach. It is pragmatically based on the power system of the French SPOT satellite. The ERS-1 power system consists of a solar array with a 1900 watt capacity connected directly to a single power bus which is in turn connected to four parallel twenty four cell, Space Power: Resources, Manufacturing and Development
RkJQdWJsaXNoZXIy MTU5NjU0Mg==