balance these loads. On Earth, this is done by integrated cogeneration units where some heat can be distributed, converted to electricity, or dumped. On the moon it would be desirable to have high temperature radiators which could dump such heat as needed either directly to space or indirectly to maintain temperature in a lower temperature radiator. Ease of Maintenance and Operation The expense of manpower on the moon is very high and the dangers from failure are very real, therefore lunar systems must be reliable and easily maintained. There are several unique problems such as the high vacuum, dust, micrometeorites and high intensity radiation. Other problems are the more standard leaks, leak detection and repair. Repairing of any system usually involves isolating, draining and shutting down the section to be repaired. Sufficient spare capacity must also be available to maintain normal services. Dust and vacuum are not a problem for completely enclosed systems except for pumps which should be canned. Micrometeorites are a real problem because the large area of the radiators means that impacts will be relatively frequent. Several techniques have been suggested including double wall pipes but there is also the simple solution of using thicker and tougher pipes. The preferred approach is to use the lunar soil to reradiate heat from the backside of the pipes thus reducing the area which can be damaged. Whatever protection is chosen, it is possible that a sufficiently large meteorite will land, or some other failure will occur to produce a leak. Therefore a leak detection and repair capability is necessary. Detection of water vapor over large distances is possible using lightweight solid state detectors. Use of heat sensors would also be useful in leak detection and in finding hot or cold spots, perhaps due to blockages. Repair capability is desirable and should be capable of all repairs from pinhole leaks to replacement of whole panels. Use of small amounts of imported materials for leak sealing is sensible with larger repairs requiring isolation and replacement of leaking sections. Normal practice will be isolation and drainage with repair of all broken sections during a scheduled turnaround. Radiator System Efficiency The overall radiator system efficiency is the key parameter which may be significantly different from the efficiency of the radiator itself. This parameter is based on the temperature of the process stream before it goes into the heat exchanger that rejects the heat to the radiator system. This temperature, To is the lowest temperature that the process system can usefully use for work of some kind. In a turbine it controls the backpressure of the system and is very important in determining system efficiency. An ideal radiator with perfect emissivity would radiate that heat at To to an environment with no back radiation. Thus the theoretical maximum radiation is oTf with o being the Stefan-Boltzman constant. Other losses are shown on Table II and the typical effect of those losses on the overall performance of a radiator system are shown in Table III. It can be seen that the two-phase system is generally better than the single phase system with the exception of the losses through the wall where a liquid droplet system has no losses. A two phase
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