The hydrogen is then recycled to produce additional methane. Additional oxygen is produced by thermal decomposition of carbon dioxide [12] or by pyrolysis of methane back to hydrogen and carbon followed by reactions (1) and (2) repeated [13], The baseline Zubrin/Baker scenario requires a 100 kW reactor running for 24 hr/day for 155 days for the propellant production. The energy required for manufacturing 107 tons of propellant on Mars is 370 MW-hrs of electrical energy. For the solar-powered case, it is desired to produce the required amount of propellant in half a Mars year, chosen to avoid the global dust storm season. The baseline case studied used the following parameters: site = Viking 1 lander site propellant production completed in half a Mars year season = northern hemisphere spring and summer insolation available = 3 kW-hr/m2 per day fixed array (no tracking) solar array mass = 0.9 kg/m2 (APSA array technology) solar array efficiency = 20% under Martian conditions storage system: none (propellant production during day only) The solar cell efficiency of 20% is about the efficiency of currently available GaAs cells operating at the temperatures expected at Mars. The solar array specific mass of 0.9 kg/m2 is roughly the target mass of a high-efficiency solar array designed for GEO [5], Mars arrays will have a different mass, since the structure will be different from GEO, but in the absence of an array designed for Mars, this will serve as an order of magnitude estimate. The global insolation on a horizontal (non-tracking) surface averages slightly over 3 kW-hr/m2 per day. Running the system for half a Mars year results in a total insolation of 1000 kW-hr/m2. No mass allocation for energy storage is assumed. The solar array area required for propellant processing is 1850 m2 equivalent to an array 43 meters square. The PV blanket mass is 1.67 metric tons, which excludes the structure to hold the array in place, the mass of a robot or remotely- operated unit to deploy the array, and the mass of power conditioning, management and distribution equipment (PMAD). If the PMAD and ancillary, equipment weight equals the PV blanket weight, the total required mass will be 3.33 metric tons. This is comparable to the baseline power system considered by Zubrin and Baker, which used a 100 kW nuclear reactor and had a total mass of 3.96 metric tons.
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