14 CFR 1216.605: Integrity and completeness of information.

(a) NASA will not undertake new scientific and technical research to inform its analyses unless it is essential to a reasoned choice among alternatives and the overall costs and time frame of such undertaking are not unreasonable. Rather, NASA will make use of reliable existing data and resources.

(b) When NASA is evaluating an action's reasonably foreseeable effects on the human environment, and there is incomplete or unavailable information that cannot be obtained at a reasonable cost or the means to obtain it are unknown, NASA will make clear in the relevant NEPA document that such information is lacking.