I just thought I’d quickly mention that the team behind DIRECT has just released a much improved revision. To put it mildly, I’m not much of a fan of shuttle derived launch vehicles, but of all the alternatives out there (including and Ares V and especially Ares I), I think that this approach makes the most sense. I was tangentially involved with the effort, and I think this proposal is a lot more solid than the previous one. The big difference is that they ditched the unproven RS-68 upgrades and the tank stretch, and made up for it on the “Heavy” version by using a 2x J-2X configuration on the upper stage.
I still think that using a propellant depot and orbital propellant transfer to disaggregate the launch portion of the transportation architecture from the in-space portion of the architecture. However, if NASA really must insist on keeping as many people in Florida, Texas, Utah, etc busy as possible, this at least doesn’t “suck all the air out of the room”. It leaves enough budget flexibility to deal with setbacks as they happen, while having more money available for funding projects that are high-risk/high-return like propellant transfer, Centennial Challenges, COTS, etc.
Quite frankly the only thing going against it as far as I can see is that it isn’t Scotty Horowitz’s idea.