On-orbit depot architectures using contingency propellant

This paper introduces new concepts of on-orbit propellant depots for human space exploration based on contingency propellant. The proposed architecture is useful in that it does not require separate depot filling missions, whereas conventional depot architectures require large "prior investment" type missions for depot filling before gaining the returns. Two concepts for this type of depots are shown: "steady-state" architecture and "stockpiling" architecture. In the "steady-state" mode, the depot always keeps the contingency propellant in orbit as well as the reused habitat module. In each mission, the vehicles collect the habitat and the contingency propellant from the depot in orbit on its way to the destination, perform the maintenance for the habitat, and leave the habitat and the unused contingency propellant in orbit on its way back. In the "stockpiling" mode, on the other hand, the habitat module is reused in the same way, but the depot accumulates propellant so that a later mega-mission can carry larger payload. Numerical results show the usefulness of the proposed architectures.