Exploration Systems Architecture Study - Criticism

Criticism

See also: Shuttle-Derived Launch Vehicle#Criticisms

Beginning April 2006 there were some criticisms on the feasibility of the original ESAS study. These mostly revolved around the use of methane-oxygen fuel. NASA originally sought this combination because it could be "mined" in situ from lunar or martian soil – something that could be potentially useful on missions to these celestial bodies. However, the technology is relatively new and untested. It would add significant time to the project and significant weight to the system. In July, 2006, NASA responded to these criticisms by changing the plan to traditional rocket fuels (liquid hydrogen and oxygen for the LSAM and hypergolics for the CEV). This has reduced the weight and shortened the project's timeframe.

However the primary criticism of the ESAS was based on its estimates of safety and cost. The authors used the launch failure rate of the Titan III and IV as an estimate for the failure rate of the Delta IV heavy. The Titan combined a core stage derived from an early ICBM with large segmented solid fuel boosters and a hydrogen-fueled upper stage developed earlier. It was a complex vehicle and had a relatively high failure rate. In contrast, the Delta IV Heavy was a "clean sheet" design, still in service, which used only liquid propellant. Conversely, the failure rate of the Shuttle SRB was used to estimate the failure rate of the Ares I, however only launches subsequent to the loss of Challenger were considered, and each shuttle launch was considered to be two successful launches of the Ares even though the Shuttle SRBs do not include systems for guidance or roll control.

The Delta IV is currently launched from Cape Canaveral Air Force Station Complex 37, and the manufacturer, United Launch Alliance, had proposed launching human flights from there. However, in the estimation of costs, the ESAS assumed that all competing designs would have to be launched from Launch Complex 39, and that the Vehicle Assembly Building, Mobile launcher Platforms and pads A and B would have to be modified to accommodate them. The LC-39 facilities are much larger, more complex, older, and more expensive to maintain than the modern facilities at Complex 37 and are entirely inappropriate for the Delta, which is integrated horizontally and transported unfueled. This assumption was not justified in the report and greatly increased the estimated operational cost for the Delta IV. Finally, the decision in 2011 to add an unmanned test of the Orion on a Delta IV clearly contradicts the ESAS conclusion that this was infeasible.