Pursuant to a congressional request, GAO provided information on the National Aeronautics and Space Administration's (NASA) historical experience at estimating space program costs.

GAO found that: (1) 25 of the 29 programs reviewed required more funding than initially estimated; (2) the median estimate change for all programs was a 77-percent increase in space program costs; (3) general reasons given for differences in initial and current estimates included insufficient definition studies, program and funding instability, overoptimism by program officials, and unrealistic contractor estimates; (4) specific reasons for changes in estimates included program redesigns, technical complexities, budget constraints, incomplete estimates, shuttle launch delays, and inflationary effects; and (5) the content and schedule of many programs changed substantially between the initial and current cost estimates.