https://www.niac.usra.edu/files/studies/final_report/320Zubrin.pdf
Authors. Robert Zubrin
Venue. NASA Institute for Advanced Concepts final report
How the Institute flags it
frontier 1 time speculative 1 time
This source carries more than one flag across the corpus. That is not an inconsistency to resolve: the same work can be established evidence for one claim and frontier evidence for another, and the flag belongs to the use rather than to the source.