Vigilant

The idea of having the title "USS" implies too much restriction on the United States as being the sole force behind the expedition. It's logical to assume that that's why none of the Space Shuttles have/had that prefix. NASA works with many people from many nations, and in 2018 it'll more than likely be a conglomerate of nations taking the trip to the moon, rather than just the U.S.

Now, to the name; Vigilant is defined as "keenly watchful to detect danger," which would add an element of irony to the idea of a world that had forgotten about the Nazis, who had been on the moon all along.