4. TRANSPORTATION Studies conducted by NASA and industry have substantiated the following fundamental SPS transportation system requirements: • New, dedicated transportation systems Earth launch vehicles (ELV) Orbital transfer vehicles (OTV) Crew and resupply modules (CRM) • Total reusability and many reuses • Minimal launch costs and rapid turnaround These requirements are driven by cost considerations and are dominated by ELV operations costs (i.e., costs per flight). There are, however, transportation considerations other than costs which affect the feasibility of SPS. Specifically, these relate to the development of traffic models which must be integrated with assembly sequences to ensure that cargo supplies are always adequate to meet cargo demands. In addition, facilities must be designed to receive the OTV's and to sort, transfer, and store the cargo. Finally, payload mixes must be developed which minimize or alleviate the need for very low density payload packaging for the ELV. To maintain uninterrupted consistency of this task, the assumption was made early that the cargo requirements for each SPS, including packaging penalties, would be 27.27 x 10$ kg (60 x 10$ lb). Although there were satellite weight growths during the study, this assumption was fortuitous in that a significant growth margin is still allowable. 4.1 EARTH LAUNCH VEHICLE The recently completed ''Systems Concepts for STS Derived Heavy Lift Launch Vehicles Study," Contract NAS9-14710, conducted by the Boeing Aerospace Company and Grumann Aerospace Corporation for NASA, compared the cost-effectiveness of a broad range of ELV boosters of different payload capabilities (payload classes) across a gamut of program annual payload demands (activity levels). Figure 4.1-1, taken from the referenced study (commonly referred to as the HLLV study) illustrates the dramatic change in program cost characteristics as a result of activity level increases. Typically, for a given concept design, reductions in dollars per pound to orbit can be achieved by designing the ELV for higher payload capabilities. This is reflected in the HLLV study by the selections made from among the candidate concepts for an ELV applicable to the SPS program. One of the two choices is shown in Figure 4.1-2 with its dimensional data and payload capabilities. This two-stage, ballistic/ballistic configuration can be configured for varying payload densities, as indicated,
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