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This paper explores the possibilities of cooling a permanently inhabited lunar base with a reverse Brayton cycle Thermal Control System (TCS). Based on an initial stage outpost, the cooling needs are defined. A thermodynamic performance model for the Brayton cycle is derived using ideal gas analysis. This model includes inefficiencies and irreversibilities of the components. The free parameters in the thermodynamic model are successively removed using limiting values for efficiencies and determining operating parameters by suboptimizations. In essence a model for cooling efficiency as a function of rejection temperature alone is obtained. For every component of the system a mass model is applied and the overall mass is determined. The last remaining degree of freedom, the rejection temperature, is eliminated by an optimization for lowest overall mass. The result for minimal TCS mass is compared to a reference TCS using a Rankine cycle.

A Capillary Pumped Loop (CPL) is an advanced two-phase heat transport device which utilizes capillary forces developed within porous wicks to move a working fluid. The advantage this system has over conventional thermal management systems is its ability to transfer large heat loads over long distances at a controlled temperature. Extensive ground testing and two flight experiments have been performed over the past decade which have demonstrated the potential of the CPL as a reliable and versatile thermal control system for space applications. While the performance of CPL's as “black boxes” is now well understood, the internal thermo-fluid dynamics in a CPL are poorly known due to the difficulty of taking internal measurements. In order to visualize transient thermohydraulic processes occurring inside an evaporator, a see-through capillary evaporator was built and tested at NASA's Goddard Space Flight Center.

A parametric analysis is performed to compare different heat pump based thermal control systems for a Lunar Base. Rankine cycle and absorption cycle heat pumps are compared and optimized for a 100 kW cooling load. Variables include the use or lack of an interface heat exchanger, and different operating fluids. Optimization of system mass to radiator rejection temperature is performed. The results indicate a relatively small sensitivity of Rankine cycle system mass to these variables, with optimized system masses of about 6000 kg for the 100 kW thermal load. It is quantitatively demonstrated that absorption based systems are not mass competitive with Rankine systems.

The lunar environment places some unique demands on a thermal management system designed for manned lunar missions. A principal concern is that for many prime base locations the effective thermal sink temperature is often near or above nominal room temperature (25°C). This is due to the fact that a conventional radiator must look at either, or both, the sun and the hot lunar surface. Direct rejection of waste heat at such temperatures is thus impossible, and some alternative approach is needed to enable a sustained mission. This paper presents three such alternative systems: a heat pump assisted central thermal bus; an innovative, selective field-of-view radiator; and use of the lunar regolith as a heat sink. All of these concepts appear feasible, but each has uncertainties associated with its practicality and weight estimate. The heat pump assisted thermal bus appears to be the most viable concept and is discussed herein in some detail.

With the use of single and two-phase heat transport systems for the thermal control of large space facilities, there will be numerous instances where fluid lines will have to traverse joints that either rotate or move in some other manner. Flexible hoses are being considered as one means of traversing these joints. They would be subjected to a variety of stresses and to as many as 150,000 rotational cycles. In order to test the resilience of flexible hoses to bending stress, a test assembly was constructed to determine the number of flexing cycles the hoses could withstand before losing their ability to maintain a constant pressure. Corrugated metal hoses of 1/4, 3/8, and 1/2-inch diameter and teflon hoses of 3/8 (smooth bore) and 1/2-inch (convoluted) diameter were tested at different pressures with nitrogen gas. The metal hoses had lives ranging from 30,000 to 100,000 flexing cycles.