For anyone who thinks it's ridiculous that the US can't reproduce the Apollo missions, consider this: we can't (due to environmental factors) produce wrought iron anymore (because there are no longer any facilities setup to do so), as a species, and therefore, could not build the Bay Bridge in San Francisco (and I'm sure, any number of others, like the Brooklyn bridge).
The same limitations apply here. They have to redesign the vehicle on first principles because the foundational engineering (not scientific understanding) being used no longer exists. Most people simply do not realize how precariously our technological world hangs in the balance. It's why highly advanced ancient cultures collapsed, in large degree: they couldn't just start at the lower level again before working their way back to 'advanced civilization', they had to start all the way at zero again.
Here's a fun one I like playing with my kids, kind of the nerdy science version of the polysci "go back in time to kill Baby Hitler: which one scientific understanding would you bring back in time to Ancient Rome/the American Revolution/the 1950s/etc. and why? Dollars to donuts they'll say something like "the lightbulb" and not consider that it's at least 3 distinct discoveries and inventions, nevermind the engineering.