launches from Kennedy Space Center (KSC) result in placement of the maximum payload of 65000 lb into low earth orbit at 28.5 deg inclination. Figure 3.1-4 presents the Shuttle payload capability as a function of circular orbit altitude for situations requiring a rendezvous by the Shuttle. As illustrated, 190 n mi is the maximum altitude that the Shuttle can deploy the maximum payload of 65000 lb. Shuttle performance degrades near linearly and rapidly above 190 n mi to 290 n mi, where no payload can be placed into orbit. Shuttle performance in this region can be increased with the addition of Orbit Maneuvering System (OMS) propellant in the Shuttle's payload bay; the obvious disadvantage of doing this is the loss of payload bay volume. Figure 3.1-5 presents similar performance information for cases not involving an ultimate rendezvous Shuttle. Maximum payload can be deployed to 220 n mi since no OMS propellant has been budgeted for rendezvous. Since deployment of segments of the SSPS will require their being placed in close proximity to previously orbited segments, the rendezvous performance curve was used to determine Shuttle capabilities. 3.1.2.2 Tug The Space Tug is an integral part of Flight Plan 2 operations since it will be used to transport, to , the material delivered to LEO by the Shuttle. The Tug used throughout this ai alysis (see Ref 1) uses cryogenic propellant, is reusable and has the following characteristics: • Propellant weight: 50177 lb (22730 Kg) • Burnout weight: 5755 1b (2607 Kg) • Specific impulse . A typical Tug scenario starts with pick-up of a payload from a 190 n mi c’ alar orbit, then delivering the pay load to a 7000 n mi circular orbit, and returning to th., shuttle in the original orbit. Figure 3.1-6 presents the Tug deploy capability while performing such a scenario. The performance is listed as a function of the delta v the Tug must expend to get the payload to its point of destination. This outbound delta-v can be related to the deployment altitude. The delta-V inquired to return to the to Shuttle has been assumed to be equal to that of the outbound leg of the joumev. Figure 3.1-7 shows the Tug configuration and summarizes its payload capability for three operation modes. The first, is for the aforementioned payload deploy scenario; it shows (as does Fig. 3.1-6) that the Tug can deploy . The
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