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a a With respect to an all-rocket SSTO launcher.

Even considering the weight of the heat exchangers, the conversion of the rocket to an airbreathing rocket to Mach 5.5 offers considerable savings in weight and engine thrust. This straightforward improvement to the rocket engine offers major cost reductions [Czysz and Richards, 1998]. For the same liftoff weight of 616.21 the payload for the airbreathing rocket systems and the KLIN cycle is between 24 and 38 tons. Had the Delta Clipper program survived and, had an airbreathing rocket been considered, the payload could have been increased and the gross weight reduced.

(3) LACE rocket-ram-scramjet, and deeply cooled (DC) rocket-ram-scramjet have the advantage of providing a weight saving equal to the ejector ram-scramjet but with an intermediate step. For the ejector ram-scramjet propulsion system the benefits cannot be realized until an operational scramjet is developed and qualified for flight operations. The advantage of the airbreathing rocket is that it can be an effective first step based on existing hardware arranged in a different manner and that can achieve approximately 60% of the eventual scramjet benefit without any new engine development. An operational system can be operating and realizing this benefit while the scramjet is being developed at its own pace, to be integrated later into the airbreathing rocket system (as A. Rudakov envisioned) to realize the final 40% improvement. During that time the airbreathing rocket system and the air vehicle have been proven in operation. No differentiation in weight is made for the liquid air cycle versus the deeply cooled. Historical data suggests that the systems are essentially equal in total system weight. For a vehicle for a rocket OWE equal to 76 metric tons and the OWE of other propulsion systems also fixed at 761, plus any differential for the propulsion system, the TOGW for the two systems is:

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