The need for gaining alternate access into space can undoubtedly enhance the Space Shuttle System to produce a strong and well balanced U.S. space program. Balance, because the use of Expendable Launch Vehicles (ELVs) with the Space Shuttle program provide reliability and flexibility in providing an alternate manned access into space. This paper focuses on an Alternate Transportation System (ATS) study conducted by NASA and more specifically the technical feasibility for providing alternate manned access into space. This is accomplished by using combinations of booster vehicles, crew modules and service modules to achieve manned access into space should the Space Shuttle be unavailable to support the Space Station. The Space Shuttle manifest could also be relieved for those dedicated Space Shuttle missions which support the Space Station directly. The three missions identified for the Alternate Transportation System (ATS) are (1) manned launch, specifically for rotating Space Station crewmembers every 90 days, (2) launch of a logistics module which will re-supply the Space Station every 180 days, and (3) launch of both crew and logistics to the Space Station. The Titan IV/NUS and Shuttle-C are discussed as booster candidates as are the Apollo and a glider assessed as crew modules. The flight elements and their associated mission profiles are defined to help visualize the configurations and understand the operational complexities. A vehicle performance assessment summarizes the different capabilities, and the results of the ATS are discussed in closing.
Before entering into discussion about the ATS study, a parallel is drawn for the sake of emphasizing the need for alternate manned access into space.