"All these unknowns, as well as others, leave NASA in the position of being unable to provide firm cost estimates for the projects at this point," it reads.

Firm cost estimates on large government projects are often fiction. They put foreward low-ball estimates to get the project started and then use the argument, "But we've already spent $xx so we can't quit now" to keep it going. How many government projects get cancelled for busting their budget. This isn't limited to high-tech projects, either. Case in point: Boston's Big Dig.