2.2.3 REPRESENTATIVE CONFIGURATION The representative configuration for a high-thrust 02/H2 CTOV is illustrated in figure VI-D-2-2. It is an expendable single-stage vehicle capable of transporting a one million pound payload from LEO to GSO. The stage requires two launches to emplace in LEO; one launch for a complete stage with an undersized LOX tank, the second launch for the remainder of the LOX in its own tank which is plugged into the stage without a propellant transfer requirement. A weight statement for this stage is given in table VI-D-2-2. 2.2.4 TECHNOLOGY ISSUES There are no significant technology issues associated with this concept. 2.2.5 COTVg REFERENCE CONFIGURATION - 2-1/2 STAGE 02/H2 A parametric vehicle sizing exercise was performed to determine vehicle ignition weights for various LEO reusable COTVg (subscript "G" denoting SPS construction at GEO) staging options including single stage, 2-stage, 1-1/2 stage, and 2-1/2 stage. The latter two options involve expending the outbound propellant tanks at GEO and returning the "core" to LEO for reuse. Parametric stage mass fraction data utilized were derived from the Boeing FSTSA study and included a 15% dry weight contingency. Results are plotted on Figure VI-D-2-3 and indicate that the 2-1/2 stage option achieves minimum ignition weight and therefore would require less HLLV Earth launch support. On this basis, the 2-1/2 stage has been selected as the reference configuration for the space transportation scenario analysis in Section VI-F and the program model analysis in Section VII. The resulting point design "nominal" configuration and data are presented on Figure VI-D-2-4. The stage 2 drop tanks and stage 1 main propellant tanks are identical in size. Using an RL-1O Cat. IV 02/H2 engine as baseline, 8 and 11 engines are required for stage 2 and stage 1, respectively, to provide the .1 G acceleration during main propulsion operations. The 2-1/2 stage payload delivery mission is performed similarly to the 2-stage except that the stage 2 outbound propellant tanks are "expended" at GEO. The empty drop tanks may be left with the SPS as parasitic weight without penalty, or perhaps even utilized in the SPS construction at GEO. During the mission, stage 1 provides approximately 1600 meters/sec of the required 4330 meters/sec one way delta velocity. Stage 1 returns itself to the LEO OTV operations depot for reuse. Stage 2 completes the transfer to GEO with its drop tank propellant. After docking with the GEO SPS construction facility and offloading payload, the stage 2 core returns itself to LEO for reuse. In the case of this high-thrust COTVg and resultant low trip time to GEO (less than 1 day), it may be possible to delete the development of a POTVg and fly the passenger carrying module as part of the large COTVg outbound cargo. This program deletion and possible cost saving may be addressed in subsequent studies should the GEO construction location and high-thrust chemical COTV be selected.
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