2. A protective device (fuse or circuit breaker) suitable for protecting a 500-amp subcircuit connected to a 100,000-amp, 40,000-volt bus. Both devices must perform reliably in the environment of Earth synchronous orbit with a MTBF of 10 years. Design must be fail-safe. Weight of a switch and protective device combined will not exceed 3 kg. The switch will be tailored to solar panel characteristics (e.g., high open-circuit voltage when cold). Types of switching to be investigated will include mechanical switches, solid-state devices (SCR's, bipolar transistor, field-effect transistors, etc.) and plasma devices (vacuum tubes, thyratrons). Control signals will be low level, available for centralized computer control, isolated from the high power circuit and fail-safe. i. Key Issue No. 9 — High Voltage Circuit Design The generation of high currents induce magnetic moments which can react with the natural magnetic environment and cause torques upon the SSPS or result in internal stresses caused by the interaction “self induced” local magnetic fields. The high voltage also could lead to corona formation or other ionized gas phenomena which could reduce the life of the component. The bussing of the high currents, in addition to the magnetic effects, also has an internal resistance associated with them. By judiciously sizing the cun-ent-carrying busses and using the structure for bussing when possible, the power losses can be optimized from a weight point of view. The solar cells can be sized to allow extremely long circuits with the necessary parallel members to eliminate the majority of the cross busses as well as the internal busses in the SSPS structure. The solar cells can accomplish the majority of the current-carrying function while at the same time generating new power. A trade-off must be investigated on the relative magnetic moment that can be accepted versus the spacing between high electrical potential current elements under the particular environment. j. Key Issue No. 10 — High Level de Power Distribution Present high-power satellite electrical systems are in the range of a few kilowatts at voltages up to 100. Transmission distances are short. Future space power systems in the multi-megawatt range will require efficient transmission lines over considerable distances at minimum weight. The objectives are to determine: 1. The optimum high-power transmission line which can be built of conventional material (aluminum). Initial design will be for 40,000 volts, 100,000 amps, over a distance of 3 miles. Conductors will be self-supporting and entire structures could be used as structural elements of spacecraft (e.g., to support a solar collector panel). Weight and cost must be minimized. 2. The trade-off between possible approaches based on ease of assembly, cost, weight, reliability (including cost of maintenance), electrical efficiency, and effect on associated systems (e.g., reduction in solar panel weight by using transmission line as a structural support).
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