Project Horizon – Technical Considerations and Plans (1959) [pdf]
nsarchive2.gwu.edu
nsarchive2.gwu.edu
Project Horizon was a 1959 study to determine the feasibility of constructing a scientific / military base on the Moon
> At present there seems to be no very urgent reason to depart from using nitrogen as the diluent for oxygen. Any mechanical advantages that may be considered for helium would be offset by its greater ease of diffusion and hence leakage, and by the high demands upon available supplies.