The following assumptions are common to all these results: (a) Two stage fully reusable vehicle (b) Fixed equipment, consisting of auxiliary power systems, controls (both OMS and RCS), avionics environmental control and furnishings of 14,000 kg for each stage (c) Fuselage mass of 0.5 x mass of contents (d) Propulsion mass of 4% of gross launch mass (GLOW) with specific impulse of where WF is the fuel mass in lbs and e is the tank mass divided by the fuel mass (f) Wing, empennage and landing gear mass of 12.5% of load supported (g) Thermal protection system (TPS) adds 50% of mass of structure protected (h) Refurbishment costs of 1% of procurement cost per launch. Figure 2 shows the cost as a function of distribution of energy between the two stages. It was assumed that a total AV of 10,000 m/sec was required for orbit allowing for gravity and aerodynamic losses, occurring mostly in the first stage. Evidently an optimum distribution occurred at close to 5,000 m/sec in both stages, a not surprising conclusion in view of the fact that both stages must pay the inert mass penalty associated with reusability. This value of AVj = AV2 = 5,000 was therefore used in all subsequent calculations. Figure 3 compares a ballistic unmanned parachute recovered first stage with a winged manned flyback first stage. Also shown is the penalty involved with enclosing the payload in a thermally protected fuselage. Figure 4 shows the effect of learning curve slope on the cost. One hundred percent implies no learning. Larger payload, WPL, implies fewer vehicles, hence less learning. Figure 5 shows the effect of development cost. From these curves it is possible to estimate the launch costs to LEO for any given set of assumptions. It has been assumed that the mass of one SPS will be 50 x 10® kg. The potential values for one typical solution, taking as an example what may be termed the base case of an unprotected payload (which assumes that the thermal loads during acceleration to orbital velocity can be absorbed by the payload with minimal protection) with a 90% learning curve and a development cost of 5,000 $/kg of inert weight were: Payload mass = 50,000 kg Inert mass fraction of first stage - . 145 Inert mass fraction of second stage - .220 Inert mass fraction of fuel tank - .050 Number of launches - 10,000 over total program GLOW = 1.53 x 10® kg Second stage separation weight = 340,000 kg. The method of solution programmed to obtain the results of Figs. 1-5 is outlined in Appendix C.
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