Lots!
and Lots.
The cadence of "builds" during Apollo was astounding, and they built the only 100% reliable rocket engine.
During Apollo even with "the best will in the world" mistakes were still made that cost lives.
but those errors totally changed the way NASA made and built stuff.
Then during the Shuttle Program more deaths caused another total rethink,
No deaths in Space since 2003
but its been easy "Space"
The cynic in me thinks in 2021 a vast majority of Yank pollies are quite happy to fund private enterprise to do all the hard yards to get to Mars,, but you can bet the first Earthian ( Earthite? ) on Mars will have a NASA logo on the suit..

