Transportation 1. One vehicle, the orbital transfer vehicle, is used to transport four passengers in one round trip: from low earth orbit to lunar orbit, then to the space manufacturing facility, then back to low earth orbit. It uses a hydrogen-oxygen rocket for propulsion, and the cost of the fuel will be assumed to be so low in comparison to other costs that it will be neglected. 2. The orbital transfer vehicle specifications are from SP-428 [9], scaled down to 4/30 = 0.133 of the size given there, because it carries 4 passengers instead of 30. The orbital transfer vehicle of SP-428 has a cabin with mass 23.4 t, and a stage with mass 6.5 t. The mass of the version used here is then 0.133 • (23.4 t + 6.5 t) = 4.0 t. 3. The orbital transfer vehicle uses 22 t of fuel in its round trip, 1.5 times the mass a vehicle of this reduced size normally would in a direct round trip between low earth orbit and low lunar orbit, since it makes a stop at the space manufacturing facility during its return to low earth orbit. This factor is only a guess, probably accurate to 50%. Half of the fuel is loaded from the mass driver reaction engine while it is in low lunar orbit. 4, Transportation between low lunar orbit and the moon is via a large transfer vehicle with specifications from SP-428. Its payload is 81 t, and mass empty 7 t [10], The design is assumed modified so that the pressurized cabin, with mass 5 t, is not used, and passengers are in pressure suits. 5. One mass catcher at the L2 point of the earth-moon system receives material from the moon, and has mass 340 t [11], 6. One mass driver reaction engine, with specifications from SP-428, is used to carry the space manufacturing facility and mass catcher into place on the way to low lunar orbit during its first trip from low earth orbit to low lunar orbit. It also carries consumables for men, the lunar transfer vehicle and its fuel, the lunar manufacturing facility, and additional equipment used in construction of later generations of the space manufacturing facility and the lunar manufacturing facility on this trip. Later, it brings additional supplies from low earth orbit. Its mass empty is 174 t, and it consumes reaction mass at the rate of 175 t/mo [12]. Its payload to L2 and low lunar orbit in a round trip without refueling starting at low earth orbit is at least 800 t, and 880 t will be assumed in calculations for asteroidal resources. Since it takes 5 months to reach low lunar orbit from low earth orbit [13], and L2 may take about the same energy and time to reach, it will be assumed that it takes 5 months to reach L2 from low earth orbit, during which time the mass driver reaction engine constantly consumes reaction mass. This is only a guess, but probably accurate to 50%. Since a direct round trip for the mass driver reaction engine between low earth orbit and low lunar orbit takes 6 months [14] the trip from low lunar orbit to low earth orbit takes one month. The trip from L2 to low lunar orbit is assumed to take one month.
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