Why does it take 10 days?
Because it's not powered the whole way. You fire the engines briefly from earth to get to near-escape velocity, then coast to the moon, all the while slowing down because earth's gravity is pulling you back. It's like kicking a ball up a hill to get it into a dip over the top: you need to kick it hard enough to just get over the hill - i.e. when the moon's gravity is stronger at that point than earth's. If you went powered all the way you'd need a lot more fuel, and you'd also need even more fuel to slow you down when you got there.
AWS architecting class years ago. Awesome instructor said if you want to save money, start deactivating servers. The ones people use... the admins will contact you right away. The others... people started up and forgot about.
"Back in the day" I identified a way to save prob a quarter million dollars a year on my project, funded with your tax dollars. Created a spreadsheet model for the cost, documented it all, and gave it to my boss. He said "I'll look it over". I asked his two weeks later if he'd been thru it. His response was "It looks correct. Nice job." I asked if were going to trial it.
Golden response: "No, we don't get paid to save money; we get paid to spend money."
And that is when I truly understood Cost+Award Fee contracting with the gov't.
My boss' (we were internal consultants) mantra was "we can accomplish anything if we don't get hung up on who gets the credit". She is one of the best I worked for.