Space Station

Improving NASA's Planning for External Maintenance Gao ID: NSIAD-92-271 July 20, 1992

Over a four-year period beginning in 1996, NASA plans to build the Space Station Freedom in low earth orbit. External maintenance for the space station during assembly and for its anticipated 30-year life will depend on astronauts' performing space walks, called extravehicular maintenance activity. Harsh conditions in space mean that the amount of such activity will be restricted. GAO found that NASA's estimates of maintenance requirements are not very reliable, partly because the project is in its early development stages and methods for predicting failure rates and replacement times are limited. Further, extravehicular maintenance activity resources will not be enough to handle all the external maintenance needs expected to arise during the station's assembly period, and a large maintenance backlog may accumulate. NASA's analysis of the backlog's impact on the space station's performance is not yet complete. Extra maintenance missions could be added, but this would increase project costs and possibly delay the assembly and use of the space station. Program officials anticipate having better assembly and maintenance estimates on which to base their allocations of extravehicular activity resources by the time the program's critical design review is completed next summer.

GAO found that: (1) model-based estimates for failure and replacement rates are inaccurate and do not account for extrinsic factors, such as human error; (2) NASA does not perform detailed reviews of contractor data to determine whether underlying assumptions are reasonable; (3) EVA resources will be insufficient to address all external maintenance needs during the space station's assembly phase, resulting in a maintenance backlog; (4) EVA maintenance planners have incorrectly assumed that EVA maintenance time will be available during assembly missions; (5) EVA maintenance during assembly and utilization flights will reduce research time, and separate maintenance flights will increase total program costs and delay the space station's assembly and use; (6) permanent staffing of the space station should increase available EVA maintenance time and visiting shuttle crews could perform further EVA maintenance duties; and (7) remote controlled robots will perform some external maintenance tasks.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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