I had a thought the other day that if Musk got in a time machine with a pile of money, how far back in time could he go and still build SpaceX?

SpaceX can only do what they do because there is no human pilot on those test flights. I know that the Navy pilots argued and argued that you need a human on board but is that really true, or did that end up destroying the space program by making the cost of failure so impossibly high?

The space race of the 60s had plenty of unmanned tests before they started manning them. Humans were not the first Earth creatures in space. If Musk wanted to go back further than maybe the 70s or 80s, his issues would have been:

1. the science hadn't been fully developed ahead of time

2. he would have had a harder time getting other people on board with his idea -- he would have been labelled a complete crackpot

3. governments may have not have been so willing to allow him to do it

The issue is really actually landing rockets vertically without humans. NASA had the concept of reusable rockets that landed vertically, but didn't action it because landing without a human didn't seem feasible.

So pretty much, not before computers were good enough to autonomously land, so at best the 2000s.

1993?

Friction stir welding was invented in 1991. Full flow staged combustion was tried out in the 1960s. GPS was available 1993. Not sure how much computing power it needs.

SpaceX was founded in 2002.

Looks like there may have been an inflection point for CAD and CNC hardware around 1990 as well that might have informed the sort of iterative process that his team likes to use.

They had no pilot on board for most of the equivalent. Ariane had no pilot on board either for the whole program.

So no. That is not the reason. Try again.