Logistics and Operations versus Heavy Lift: Examining Approaches to Human Exploration in a Cost-Constrained Era

Abstract

Although recent review panels have called into question the economic viability of advanced heavy-lift vehicles, the conventional wisdom still demands some form of shuttlederived heavy-lift launch vehicle prior to initiating human exploration beyond low Earth orbit. Recent publications by the author have demonstrated that existing evolved expendable launch vehicles, specically the current version of the Delta IV Heavy, along with a smaller human spacecraft and in-orbit modular propulsion stages, are capable of supporting a robust and extensible program of human lunar exploration, starting from single-vehicle lunar orbital missions to ve-launch scenarios for lunar landing and return. This system provides routine lunar surface access for both humans and cargo, based on a architecture utilizing a low lunar orbit logistics site for stockpiling propulsion stages and supporting the assembly of lunar landing vehicles via autonomous rendezvous and docking. These prior publications have also documented probabilistic risk analyses which demonstrate that the modular approach is capable of equal or higher reliability than a monolithic heavy-lift mission, due to redundancy in propulsive options from active spare propulsion vehicles based in low lunar orbit. This paper continues and extends the analysis of a cost-constrained modular approach to exploration by examining the potential of such a system to provide access to other Flexible Path sites, including human missions to near-Earth objects and Mars orbit. In some cases, in-space technology additions such as inatable habitats for longer-duration human missions will suce to support these extended-range objectives. For the dicult goal of human Mars missions, the analysis will examine the feasibility of human missions supported solely by current EELV launch vehicles, and will perform trade studies against missions with smaller numbers of launches by investigating the impact of larger modular propulsion stages and larger vehicle currently under private development. Even with these far more ambitious mission objectives, the analyses documented in this paper still supports the basic concept of \spend the money ying, rather than postponing human exploration to await the more elegant solution of heavy-lift launch vehicles.