SPS Feasability Study SD76SA0239-2

A second approach to maximize the utilization of the payload capability of the ELV is to match the weight of each OTV stage and GEO payload to the capability of the ELV. But this matched stage-payload approach implies that two 91,000-kg OTV stages must be capable of delivering 91,000 kg to GSO. At inclinations on the order of 28 degrees, the initial LEO altitude is in the Van Allen belt region. However, if the initial inclination is equatorial, then the LEO altitude at which GEO payload and OTV stage weights are equal is about 556 km (300 n mi.). The reference ELV concept design was iterated to reflect this capability—91,000 kg (200,000 lb) payload delivered to a circular, 556-km (300-n mi.) equatorial orbit. Thus, 12 instead of 14 earth launches per day would be required to deliver 364,000 kg (800,000 lb) each day to GSO. The LEO-to-GEO logistics of the OTV was based upon the flight profile illustrated in Figure 4.2-2. The applicable AV budgets are tabulated in Table 4.2-1. As some of the maneuvers are performed by the auxiliary propulsion system (APS), an equivalent delta main propulsion system budget was established by the ratio of the Igp's of the APS and main propulsion system . The capability of the OTV is presented graphically in Figure 4.2-3. A 91,000-kg payload can be delivered to GEO from a 556-km equatorial orbit only if the return of the two OTV stages to LEO is required. A crew rotation and resupply mission of 37,192 kg (82,000 lb) up and 21,775 kg (48,000 lb) down from GEO also is indicated. The characteristics of this mission are subsequently derived. Figure 4.2-2. OTV Flight Profile