NASA’s Human Exploration and Operations Mission Directorate faces a significant integration challenge as it attempts to develop a mobile launch support structure for an evolving Space Launch System (SLS), the agency’s inspector general (IG) concluded in a Sept. 25 audit.

Nonetheless, the IG endorses the agency’s plans to modify Constellation Program Ares I hardware as the most cost-effective approach. The agency already has invested $234 million in Constellation’s Ares I Mobile Launcher at the Kennedy Space Center in Florida.

Plans to ready the 70-metric-ton payload, or smallest, version of the SLS for a 2017 initial unpiloted test flight are driving early decisions on conversion of the Ares 1 mobile launch structure, which may not be compatible with yet-to-be-decided decisions driving the eventual configuration for the largest, 130-metric-ton version of SLS, IG Paul K. Martin notes in his report.

The larger SLS, which together with the Orion/Multipurpose Crew Vehicle (MPCV) and Ground Systems Development and Operations (GSDO) program form the cornerstone of NASA’s future human deep-space exploration plans, is tentatively scheduled for an initial launch in 2030. The elements are managed separately by the Marshall Space Flight Center, Johnson Space Center and Kennedy Space Center — another factor in the integration challenge, according to the report.

NASA’s decision to modify the Ares 1 Mobile Launcher for the SLS was based on an internal assessment as well as an independent look by consultants Reynolds, Smith and Hill that placed the costs at $54 million-$74 million, depending on further modifications, including changes to the converted platform’s 355-ft.-tall umbilical tower.

The cost of reworking one of NASA’s space shuttle Mobile Launch Platforms was pegged at $93 million, while starting anew was estimated at $122 million.

Work on the Ares 1 Mobile Launcher was completed in August 2010 at a cost of $234 million, six months after President Barack Obama announced the cancellation of the George W. Bush administration’s Constellation Program.

Based on a five-segment version of the space shuttle’s solid rocket booster, the Ares I crew launcher was to pair with the larger Ares V cargo lifter to establish a human lunar base and support eventual expeditions to Mars under Constellation.

“In our judgment, development of an effective Exploration Systems Integration structure that includes baseline technical agreements is essential to ensure that requirements are effectively communicated among the SLS, MPCV, and GSDO programs. Additionally, a well-coordinated management structure will help ensure that each program reassesses the budget and cost implications of changing assumptions and configurations as the SLS Program evolves,” Martin notes in a audit that cautions NASA cannot yet rule out the need for a new mobile launch structure.

The space agency is in the process of formulating an exploration systems integration plan to facilitate communications. William Gerstenmaier, NASA associate administrator for Human Exploration and Operations, acknowledged the audit’s findings in a Sept. 21 letter of response to the IG but did not offer further comment.