Figure 2.9 Propellant Usage Breakdown for a Sample Satellite in a 900 km Orbit Power needs in space include command circuitry, thermal control, and general spacecraft maintenance tasks on both manned and unmanned spacecraft. Specific areas include the wiring harness, or power distribution system; mechanisms such as deployment systems for antennae or solar panels; thermal control, both heating and cooling; and TT&C, which includes data storage and transmission as well as command electronics. For manned spacecraft, power usage for life support would also fall into this category. Life support systems introduce additional demands for climate control, lighting, and cleaning and recycling of air and water. On Mir, the only operating manned space station, life support consumes about IkW of power per crew member out of a total power system of around 25 kW. Figure 2.10 shows the power breakdown for a typical satellite. [Chetty, 1991] Figure 2.10 Power Breakdown for a Typical Satellite Satellites, interplanetary probes and information systems applications have similar energy needs. Power is required for sensors and experimental packages, as well as data transmission systems, whether point-to-point, broadcast, or relay. For a small satellite producing a total of about 1 kW of power, experimental payloads might take up 350 W while communications would take up about 100 W. A greater proportion of power would be used for the data transmission systems for commercial communications satellites, where the payload is largely made up of more communications systems.
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