This SBIR initiates a technology program to develop affordable cryogenic and storable fueled Rocket Based Combined Cycle RBCC vehicles for space access missions. The cryogenic fueled RBCC is the 2nd stage of a Two-Stage-To-Orbit TSTO vehicle that has been boosted by a JP fueled turbine based 1st stage to 3,500-4,500 ft/s. The storable-fueled RBCC is a 1st stage that boosts a cryogenic fueled rocket 2nd stage to 8,000ft/s. Conceptual designs of three candidate space access vehicles serve as the basis for defining the engine flow paths, sizing the ejector-injector motors, identifying the key technical challenges, defining the test cell apparatus, and planning for vehicle development. A key element for affordability is the development of low cost ejector-injector motors. A significant portion of the Phase I effort will be directed to this task. The test apparatus will be sized for testing in the USAF Edwards, CA Test cells 2a and in a research facility. The ejector-injector motors will be fabricated and tested in Phase II.The principal tangible products of this SBIR will be the design of three RBCC powered vehicles for space access missions and the associated ejector-injector motors. Low cost cryogenic and storable fueled ejector-injectors will be developed for general use in RBCC engines. Both military and commercial customers are anticipated for these space access vehicles and these key engine components. Two major aerospace companies have reviewed and strongly endorsed this SBIR Proposal. Both companies will closely follow the progress of the Phase I effort for consideration of becoming Fast Track sponsors of a Phase II effort. Marketing of the vehicle concepts and ejector-injector motors will be initiated during the Phase II Program and the capitalization effort of PYRODYNE for Phase III and beyond will be initiated