Between 1967 and 1969 NASA engaged in quite a large battle over what spacecraft they should build next to get to low-Earth orbit and they space station they were sure they'd be building in the 1970s. Eventually the idea of a winged orbiter won and for better or worse we got the Space Shuttle.
However the other contender was to build another ballistic capsule on an expendable launcher in the line that had gone from Mercury to Gemini to Apollo. Both of the proposals that had any chance on this side were derived from the previous spacecraft: either adapt the Apollo CSM, or co-opt work that McDonnell Douglas had been doing for the USAF's soon-to-be-aborted Manned Orbiting Laboratory.
That second one was the "Big G", and it's the topic for the latest False Steps. Enjoy!