subsequently deliver partially assembled components to synchronous orbit or possibly to an intermediate orbital altitude for final assembly and deployment. Transportation The space transportation systems which are being considered are primarily an extension of existing systems. The potential systems, starting with the space shuttle now under development, vary from the use of a modified space shuttle to the development of a fully reusable liquid oxygen/liquid hydrogen heavy-lift launch vehicle with a potential 400,000-lb payload capability to deliver to low-earth orbit. The current shuttle or its modification can be used for SSPS technology verification and flight demonstration and for transporting elements of the prototype SSPS into low-earth orbit. The cost for such a system capable of lifting payloads up to 160,0001b to low-earth orbit, is projected to be $100-200/lb. The heavy-lift launch vehicle is expected to reduce payload costs to between $20 and $60 per pound for delivery to low-earth orbit. The large mass of payloads will require about 60 flights for each SSPS assembled in synchronous orbit when an advanced space transportation system based on heavy-lift launch vehicles is used. Ion propulsion, using solar power sources, could be used to transport a completely assembled SSPS from low-earth orbit to synchronous orbit. There is the option to transport to an intermediate orbit at 7,000 nautical miles. Chemically powered stages would transport payloads from low-earth orbit to this intermediate orbit, which lies outside the Van Allen Belt and ion propulsion would transport the assembled SSPS to synchronous orbit. The cost for each flight will be strongly influenced by the feasibility of using ion propulsion for the orbit-to-orbit transportation and by the ability to reuse most of the components of the space transportation system for a large number of successive flights. Challenges inherent in the development of a low-cost, heavy-lift space transportation system are being explored.8 The achievement of low-cost space transportation will be essential to the commercial success of the SSPS. Assembly The large number of components, most of them performing the identical function, and the role of man in assembling these components require that the methods of assembly, packaging of components, assembly rates, and maintenance and repair support facilities required during the assembly and subsequent operational phases be carefully evaluated. There are two basic approaches to assembly: (1) Remote assembly using ground controlled tele-operators.
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