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Table II-11: Propellant Required for Different Staging Strategies, 63.1 t vehicle Strategy TMI, 4 km/s MOI, 1 km/s TEI, 1.6 km/s Total Above Ideal Mdry, t Mprop, t Mdry, t Mprop, t Mdry, t Mprop, t Mprop, t 1 stage 140.7 207.6 112.2 28.5 78.1 34.1 270.2 131% 3 stages 134 197.6 102.8 26.1 68.1 29.7 253.5 117% Refuel TEI 97.9 144.5 78.1 19.8 78.1 34.1 198.4 69% Refuel MOI, TEI 78.1 115.2 78.1 19.8 78.1 34.1 169.1 45% Refuel GTO, MOI, TEI 78.1 59.5+31.6 =91.1 78.1 19.8 78.1 34.1 145 24% Ideal 78.1 70.8 78.1 17.7 78.1 28.3 116.8 0% III. Options for Pre-Positioning Architectures This section presents the high-level crewed MTV architecture for each of several cases. Each subsection summarizes the concept of operations for a given architecture, and provide tables of the module masses and launch manifests. The following options are considered: • The Mars DRA-5 baseline, with 5 SLS launches to assemble the vehicle completely in LEO. • Our proposed alternative architectures, where water is pre-positioned ahead of the MTV. o HEO assembly and departure. o LL2 assembly and departure. • Each of the above are considered for both 300 s and 450 s electrolysis propulsion performance. Generally, 450 s performance eliminates two SLS launches over the DRA-5 baseline of five required, while 300 s performance only eliminates one. • In both cases, two FH launches can replace each additional SLS launches, if desired, and architectures that do so are also presented. • Only the case of 450 s specific impulse includes an architecture that replaces all of the SLS launches with FH launches, but doing so requires more total launches. The benefits of doing so depend on the available launch rates and costs for FH and SLS, neither of which are certain as of this writing. These architectures are compared in Section IV, especially with respect to the total number of launch vehicles required for the crew vehicle to be assembled. All architectures have a number of features in common with the DRA- 5 crew vehicle: • The transit habitat is identical (41.3 t) • The Orion crew vehicle is identical (10.6 t) • The existing cargo missions remain the same. In some architectures, an additional cargo mission to deliver water propellant to Mars is added. The launch vehicle used for this is counted when comparing architectures for their total number of launch vehicles. • The departure date is the 2035 launch window to Mars, for a 180 day conjunction class mission. • Surface operations and the DAV remain identical. • The crew vehicle captures into the same Mars orbit. • From supplies consumed and/or jettisoned when no longer needed, the habitat mass decreases by 2.65 t before MOI, and by an additional 7.94 t before TEI. There are also some changes that are common among the new architectures considered: • With the vehicle being much less massive in general than the DRA-5 crew vehicle, the mass of the propulsion module for it is reduced from 15.1 to 6 t. • RCS propellant loading is reduced, for the same reason. • 5.1 t of solar panels (170 kW) are added to the crew vehicle. • The solar panels will have degraded and, even if the transit habitat is to be reused, should be replaced after each crew mission. Therefore, most of them are jettisoned after electrolysis for trans-Earth injection is complete, but before the maneuver takes place, to reduce the amount of propellant needed. 12 American Institute of Aeronautics and Astronautics Downloaded by NASA LANGLEY RESEARCH CENTRE on January 30, 2018 | http://arc.aiaa.org | DOI: 10.2514/6.2018-1537PDF Image | Water Electrolysis for Propulsion of a Crewed Mars
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