Summary: 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.
