a heater to heat/cool the gas provides a sensitive mechanism of control. Rather than heating the gas to provide the necessary force, one can simply start with a gas cylinder with a slight overpressure. Analysis We fabricated the radiator model and measured the thermal characteristics. Figure 3 shows the fabricated radiator. The radiator length, width and radiator fin thickness are 1.45, 0.15 and 0.0006 m, respectively. The shape of the coolant flow tubes is a U, with 0.05 m between the two prongs of the U. Pipes with a diameter of 6 mm are connected to the radiator for coolant intake and exit. The diameter of the rolled-up radiator is 0.18 m. Figure 4 shows a schematic of the thermal experiment. The radiator was hung vertically in a space simulation chamber using fine wires to minimize heat loss. The simulation chamber has an inner diameter of 2 m and a depth of 3 m. It is covered by a liquid nitrogen shroud of diameter 2 m, depth 2 m. Thermocouples were attached to the radiator surface for temperature measurements. The coolant temperatures at inlet and exit were measured at the junctions of radiator and the respective pipe. Water was used as the coolant and the coolant pressure atmosphere. The coolant inlet temperature was controlled by an electric heater. Figure 5 shows the radiative film characteristics of the radiator surface. A thicker radiator film means higher infrared emissivity, but it also is less flexible and has a higher probability of detaching when the radiator is unrolled. Therefore, we selected an optimum thickness of 12 /zm using an unrolling test.
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