About two dozen different mission segments can be identified for the various missions encompassed by the Vision for Space Exploration (VSE). Clearly, many crewed space vehicles will be needed on the several decades to be spanned by a return to the Moon, a Lunar outpost, and a human mission to Mars. A number of different vehicle types will be needed to operate in the different environments. Furthermore, technology will change overtime.
This paper addresses two issues: how many types of life support system will we need for these diverse missions, and how many copies of each will we need? A manifest has been developed for discussion. Based on this manifest, numbers of vehicles have been identified. Possibilities for reuse and of impacts from commercial operations will be considered.
Vehicles will be needed for launch from and landing on the Earth, the Moon, and Mars. Vehicles will be needed for transit segments. Surface habitats will be needed. Nevertheless, from the life support perspective, the main driver will be mission duration. VSE durations appear to clump into short and long missions. Thus, we may need as few as two types of life support systems: for short and long missions. Gravity might drive differences between surface operations and Mars transit operations, but this does not appear to be the case to any great degree.
The crew exploration vehicle (CEV) will be the first vehicle developed and will continue to operate throughout this period of several decades, for a total of perhaps two hundred missions. To support this spread of time, the ability to be upgraded is critical. This will also make it amenable to evolution. It is not too much of a stretch to imagine that the CEV life support system can evolve to support all the short term missions identified here. It is also likely that the short term life support system (LSS) design can be evolved to accommodate long term missions.