(3) The Space Tug (ST), a small space-based reuseable stage that would be a second stage to the CPS. It would be delivered to orbit by the EOS or the CPS. (4) The iori propulsion stage (IPS), a large space-based solar electric ion stage that would deliver SSPS subassemblies from LEO to synchronous orbit. Projected cost and performance data for the IPS were obtained from NASA-Lewis and industry sources; the overall specific power system weight (Ib/kW) of the IPS was based on SSPS solar array technology. The all-chemical STS consisting of the EOS, CPS, and ST yielded delivery costs to synchronous orbit between $300 and $500 per pound. The mixed chemical-ion STS consisting of the EOS, ST and IPS projected costs of $ 100/lb and became the baseline transportation system for operational SSPS delivery. This baseline system thus projects a transportation cost of $2.5 billion for delivery of a 5000-MW operational SSPS. A comparison of the capabilities of the space shuttle now under development with the requirements for SSPS shuttles is shown in the table on page 132. The space shuttle now under development provides the necessary first step towards a high- volume, low-cost transportation system for an operational SSPS. Further, advanced single-stage Earth orbit shuttle concepts have recently been proposed (68, 69) that show promise of reducing projected SSPS transportation costs to less than $100/lb. These large reductions in operational costs will provide the incentive to invest in the development in a new space transportation system, when the decision to deploy an operational system is to be made in the early 1990's. Recent assessments of SSPS assembly operations have indicated that a desirable location for SSPS assembly is a medium altitude orbit (5000 to 7000 n. mi.) located above the high radiation regions that would affect solar cell performance. In this concept the SSPS flies itself to synchronous orbit from the medium altitude (assembly) orbit using its own ion propulsion system. The combination of advanced single stage to orbit transportation system elements and assembly operations at less than synchronous altitudes provide optimism that a $50/lb goal, for transportation costs associated with the delivery of the operational SSPS, is potentially achievable by the 1990's. Based on these considerations, the transportation to orbit and assembly cost projections are as follows: (1) Prototype SSPS (a) $1380/kW for SSPS baseline design and “current” space shuttle transportation costs and projected assembly costs, and
RkJQdWJsaXNoZXIy MTU5NjU0Mg==