Evolving to a Depot-Based Space Transportation Architecture

Abstract

Substantial amounts of work have been expended in the past years evaluating the benefits of propellant depots for Lunar exploration. The advantages of these depots are enormous and they provide unmatched performance and reliability benefits once the technology is matured. However the maturation process itself represents a significant challenge. In a cost-constrained environment a step-wise and evolutionary approach to the development of this critical technology is optimal. Such an approach takes on risks in smaller, less costly increments. A foundational functionality is achieved as early as possibleenabling learning by direct experience. Subsequent steps benefit from concrete data and design refinements. The proposed evolution plan utilizes existing launchers and upper stages coupled with orbital test beds to move from the theoretical position of today to a depot design founded on test data but using existing aerostructures, tanks and equipment. The benefits of this very basic LEO depot as well as subsequent L1 or L2 based depots are shown for missions other than lunar landings. These range from robotic advanced capability probes to virtually anywhere in the solar system to more ambitious manned missions to near earth asteroids and the moon. With the technique of orbital propellant transfer secured by years of experience a practical architecture for indefinite stay Martian exploration can be readily envisaged as a direct extension of lunar operations. Mars’ gravitational environment implies that single-stage-to-orbit vehicles that can reenter without significant aerobraking are practical. Mars orbital propellant depots coupled to these SSTO vehicles enables a strategy of global reconnaissance and exploration.