The total shuttle payload is thus 2391.404 t + 214 t = 2605.404 t. Since the payload capacity of the mass driver reaction engine is at least 800 t, 3 trips with payload 800 t, 800 t, and 791.4 t suffice to carry all required payload to the moon and L2. Since the mass driver reaction engine takes 7 months to make a round trip, 14 months pass between its first and last departure from low earth orbit. Since the time to bring all payload to low earth orbit on the shuttle is 34.7 mo., the remainder of month 34 is used to load the mass driver reaction engine, which then makes its last departure from low earth orbit at month 35. The first mass driver reaction engine departure from low earth orbit is 14 months earlier, at month 35 - 14 = 21, the second at month 28, and the third, as just noted, at month 35. It will now be shown that enough powdered external tank mass is available for mass driver reaction engine reaction mass at the time each trip departs from low earth orbit. Since 30 flights per year of the shuttle for payload take place, or 2.5 per month, the mass available from this source by the first mass driver reaction engine departure at month 21 is mo. tanK During the 7-month round trip, since reaction mass is consumed at the rate of 175 t/mo., a total of of reaction mass is required, so the supply is adequate for this trip. By the second departure. of mass from tanks from shuttle flights carrying payload has become available. Since the first mass driver reaction engine trip used 1225 t, the remaining mass of 1225 t from this source is adequate for the second trip. The total amount of reaction mass required for all three trips was found above, and enough provided from tanks from shuttle flights for purposes other than this plan to yield the required total, so the third is also provided with adequate reaction mass. The first mass driver reaction engine trip reaches L2 at month 21 + 5 = 26, and low lunar orbit at month 27. As will be shown, it must carry
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