https://path-2.narod.ru/design/base_e/msit.pdf
Authors. Dana G. Andrews and Robert M. Zubrin
Venue. Journal of the British Interplanetary Society 43 , pp. 265-272
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.