How much extra the cost would be is unknown presently. Other recommended battery alternatives include Ag-Zn for example, although they are 3-5 times heavier than lithium batteries per Whr. (It is important to note that this is not a problem for the advanced demonstrator as the Astro-SPAS lithium batteries are already qualified for Shuttle operations.) Thermal control is passive and achieved primarily by the user designing the pay load to withstand extremes of temperatures experienced during a Shuttle mission. The GAS canister is normally insulated throughout, with only the top able to act as a radiating surface. Therefore, directly dissipating the heat from a Powersat experiment using hundreds of watts of power will be difficult. If a microwave experiment was being conducted, the antenna may have to double as a radiator. However, this would almost certainly be insufficient for the few minutes the experiment may last, even if conducted in the Earth’s shadow and space facing. Further, it is unlikely that NASA would allow a radiator to be “deployed” over the side of the GAS can because of the potentially hazardous situation of not being able to retract it after the experiment. Therefore, it may be necessary to attached the source (microwave and laser) to several kilograms of metal and use it as a heatsink. Alternatively, a phase-change heatsink could be used (e.g. Sodium- or wax-based). After the experiment, the heatsink would gradually radiate the absorbed heat. The drawback with this approach is that it reduces the amount of pay load mass that can be carried in the GAS CAP. The extra expense of lithium batteries might be a price worth paying if a heavy heat-sink was needed. Potentially, other problems could include interference from the microwave source with the Orbiter systems. Such restrictions may limit the experiment to lasers only. Another problem is the rate at which the subsatellite spacecraft is deployed and when it can unfurl or inflate. No guidelines are presently available, although a similar inflatable experiment was conducted from the Shuttle in 1985, and it failed to inflate properly.
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