Radiator

Typical figures for radiator specific power used in propulsion studies are about 5 kW of radiated power for each kilogram of radiator mass. Since the radiator can also be the heaviest propulsion component, its mass should be minimized. Values up to 100 kW of radiated power for each kilogram of mass can be envisaged. Radiator efficiency (e.g., power radiated/unit mass) depends on cycle temperature and material. To improve radiating power the temperature should be the highest compatible with cycle efficiency and material structural limits. At this time industrial practice for space power generation assumes "low" cycle temperatures of the order of 800 K to 900 K. If sufficiently large power is available, there is no reason to stop the "low" temperature from being raised, using current high-temperature ceramics (nitrides and carbides), to 1,200°C without structural problems, thereby reducing substantially radiator mass. This strategy has not yet been adopted or even tested, since known experience with large space power generators (say, >20 kW) is essentially nil. Nuclear space power generation will in fact have substantial impact on radiator technology. In any event, it seems advisable to investigate how to better exploit rejected heat prior to its disposal via a radiator (e.g., utilizing thermionics or other more advanced physics). An assessment of the available technology is in order.

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