I saw George Sowers and Bernard Kutter, from ULA, at the AIAA conference in Pasadena last week. Jon Goff has a summary/review of some of the papers they presented there.
These are key technologies for my Kickstarter project (and opening the solar system). It’s interesting to note that they think they are ready to build depots now — Congress can’t prevent it any more by cutting technology funding. I asked Bernard in his presentation if it was fair to say that ACES was basically a depot with a propulsion system. His answer: “Basically yes.” Also, what they are calling “distributed launch” is essentially a powerful refutation of the argument for the need of SLS. But they can’t say that explicitly. I asked Tory on Twitter if he could give me a ballpark price of a Vulcan/ACES flight. He demurred, but it’s a number I need to cost architectures.