The goal for a future heavy cargo launch vehicle can only be one single criteria: minimum transportation cost; considering the total effort required for launching only one SPS. Minimum cost, however, leads to the following design groundrules: 1. Fully reusable — The complete launch system must not include any expendable hardware; the goal is 50 to 100 reuses with minimum refurbishment. 2. Unmanned — For heavy cargo transportation man is not required. The pressurized cabin, the life support and safety systems are a payload penalty and increase cost. 3. Minimum number of stages — Each stage represents its own system development plus interfaces. Operations and management effort increases with number of systems. 4. Technical simplicity — Minimum technical complexity onboard is required to minimize development, fabrication and refurbishment cost and to increase reliability. Simplicity is more important than performance increase. More payload is most economically achieved by increasing the total vehicle size (lift-off mass): the penalty is essentially a larger tank size and more propellants — the cheapest items of a launch vehicle. 5. Minimum fleet size — The total vehicle fabrication and refurbishment cost are increasing with fleet size, as well as the direct operations cost. 6. Optimum number of reuses — There exists a (yet unknown) optimum number of reuses where the total of vehicle fabrication and refurbishment cost reach a minimum. 7. Operational simplicity — Operations cost represent the largest cost share in case of fully reusable vehicles. Therefore, the design must take into account minimum operations effort and shortest possible turnaround time. VEHICLE CONCEPT COMPARISON Selected Alternatives Figure 2 shows schematically the scenario of possible launch vehicle concepts to which the ground rules established in the previous chapters can be applied. The most promising solution is the single-stage ballistic vehicle with a ground-based chemical OTV. This would constitute a supplement (not a replacement) to manned winged vehicles preferred for manned operations. For verification of the most cost effective technical solution three alternatives have been analyzed from the performance and cost standpoint in more detail: A. A single-stage vehicle to LEO (SSTO) plus an orbital transfer vehicle (OTV) to GEO (and back to LEO). B. A two-stage vehicle to LEO plus an orbital transfer vehicle to GEO (and back to LEO). C. A two-stage vehicle with direct injection into the LEO/GEO transfer orbit. Final injection into GEO (apogee impulse) is performed by an expendable kick stage. Launch Cost Assessment The cost comparison has been based on a cost model published in (1) and (2). It comprises the following cost elements:
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