Go4theGusto wrote:
Theoretically, how far back did we have the (potential) capability to send a human above ~100km and bring them back? It wouldn't necessarily have to be a full-Earth orbit.
"In theory" you can have a pre-1900 "space" flight depending on how much you push your POD. At work currently so I can't use "search" but I recall at least two such threads where you had a plausible, (not necessarily SURVIVABLE mind you

) Victorian space flight attempts could be made.
Other than pushing 'rocket' technology at an earlier time you are hard pressed to get a viable interest in such a stunt, (and it IS actually a stunt and arguably STILL one even in the 1950s) because there are no actual 'operational' requirements significant enough to push for such a flight.
Despite a current trend in thinking people were somehow "less" risk-averse in the 40s-60s in reality those in charge were pretty much as 'averse' as today given a similar set of circumstances and justifications. Keep in mind that there were volunteers asking to be shot into the air on captured V2s DESPITE how unreliable they were yet "those-in-charge" kept denying them that opportunity. For good reasons actually as it was VERY unclear how such a flight would affect them AND (more importantly) no real reason to try! More so there was a real possibility that any incident resulting in death or injury for the "pilot" would have a very negative effect on both public (and more importantly) political support for continued rocket research.
Keep in mind that in the US for one "rockets-and-missiles" were classified as "Buck Rogers fantasy" and "rocket powered aircraft" and supersonic flight were barely tolerated and then only because they appeared to be a direct evolution of aircraft technology. The USSR didn't want to call attention to its rocket research programs,(which launching and announcing a manned flight would have done) as they were already under far to much scrutiny for technology they didn't in fact have! (The "Ghost Rockets" of the late 40s for example) Then there was Britain which while it did have those thinking in that direction, (Megaroc) didn't have the political or public will to pursue such projects.
Getting "someone" in power more interested at an earlier date, (TheKutKu suggests Hitler in 1933-ish) has possibilities but how significant the changes to reach a POD is questionable. Having more and significant interest in the work of Goddard for example would require someone to both stand up for him publicly, (aka taking the New York Times to task for example as they didn't print a conciliatory editorial until AFTER Apollo 11 was on the way to the Moon) as well as financially AND probably more important convincing him to expand and share his work which he was not inclined to do. (Much like the Wright Brothers before him Goddard's insistence on patent rights and province of work was very detrimental overall)
It's the 'convincing' part that's the hardest to find a POD for in that there is really no real acceptable foundation for early human space flight, even before you address the actual technical hurdles. As an example if we suppose that in 1948 Dewey had won instead of Truman it is pretty well known that Dewey favored higher Defense spending which could have translated into more money for missile research at a critical time. On the other hand the Air Force at that point had already decided to pursue advanced manned bombers and cruise missiles as a more 'near-term' solution than ballistic missiles so it is arguable the increased funding would not have flowed into missile development. (Keep in mind that even after the Korean War broke out in 1950 and the influx of funding for the military the Atlas was not given high priority till 1952 and even THEN the Air Force didn't actually make the program a priority until forced to in 1954)
Having someone outside the US or USSR produce an earlier manned flight is somewhat problematic as well. While it can be argued that either Britain or France might have gotten a 'bug' to do such a project to step out of the shadow of the US/USSR I'd have to wonder if the actual ability to do so were present at the time? Possibly as both saw some 'planning' in that direction but one wonders what the reaction would have been from the US/USSR over having done so? I suspect significant degenerating of the accomplishment as being 'only' a stunt would be automatic which would actually play worse later down the line for the US than the USSR given their lack of orbital capability. Of course the real fun is playing out someone other than the 'usual' suspects such as Brazil, Argentina or maybe Switzerland? In such a case while it IS only a 'stunt' it would have come from out of left field and virtually blindsided the "main" players which would have VERY interesting ramifications I suspect
Randy