No doubt there was a lot of eye-rolling at NASA headquarters back in May when the Government Accountability Office faulted the agency for its lack of rigor in estimating life-cycle costs for the heavy-lift Space Launch System (SLS). Certainly no one there who wants to see the big booster built is eager to draw attention to its price tag. But no one knows the costs of SLS or any of the other hardware NASA needs to fulfill its mandate to explore space. The best the National Research Council could do, after 18 months of study, is say "hundreds of billions" of dollars to land humans on Mars (AW&ST June 23, p. 38).
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