By now, the problems with NASA's Exploration Systems Architecture Study are bleeding out for the public to see. Major changes to Ares I to compensate for no air-start SSME on stage 2, possible substitution of RS-68's for the horribly expensive "expendible SSME's" on the Ares 5, a shrinking CEV, and no more methane in the CEV or LSAM. Now it's looking like NASA is having to drop the entire mission architecture in favor of either 1) rendezvous at L2 instead of earth orbit, or 2) de-scoping the project so that it's no better than the original Apollo.
Jeff Bell, the devil's advocate of the space community, has a good piece on SpaceDaily
listing many of the problems (although we happen to disagree sharply on the methane issue.) Also, Rand Simberg goes into detail
about why L1, and not L2, is the best place to rendezvous the two components of the lunar spacecraft.
Unless NASA slams on the brakes right now, the lunar return mission will be killed by the Congress that takes office in January 2007. The current choices are equally unacceptable. L2 rendezvous is risky and would require more money to be spent on lunar communications spacecraft (perhaps Lunar Recon Orbiter can last until 2018 and double as a comm relay.) De-scoping the operation back to Apollo means we will be left with an expensive, unsustainable architecture for permanent lunar settlement.
Michael Griffin took some advice from Barry Bonds and demanded a juiced version of Apollo. While the ESAS plan is still expensive like Apollo was, it had seemingly more traceability to a future lunar base (due to its more capable lunar lander, which enabled access to all latitudes and longer surface stays with highly-capable rovers.) The "Walmart" lunar lander under discussion sounds like it could be a carbon copy of the Apollo LM (except that the contractors will reinvent the wheel on the Walmart lander, because it means bigger profits.) The only similarity between Walmart and a lunar landing is that, if NASA doesn't get it's act together soon, the next manned spacecraft on the moon will be "made in China."
From my perspective, NASA is straddled with the costs of two new launch vehicles, both of which are viewed as under-performing in light of the spacecraft mass. I propose that NASA whittle their stable down to just one of the two boosters, and base the moon mission around that booster.
1) If NASA sticks with Ares I, it will have to assemble the lunar spacecraft in more than the "1.5 launches" proposed under the original plan. That's not inherently bad, as an economy of scale can be built around launches of the smaller Ares I. Rendezvous between spacecraft components can take place at L1 (my preferred option,) or they can take place in LEO (as Von Braun wanted for Apollo.) The LSAM would be launched with its propellant tanks empty, then fueled by subsequent tankers launched into LEO.
2) NASA could also elect for a two-Ares 5 architecture. In Robert Zubrin's The Case For Mars
, he illustrates one way of doing this (with his shuttle-derived "Ares" heavy lifter.) One Ares 5 launch would put an unmanned, fully-fueled return vehicle on the lunar surface. The second Ares 5 would launch a crewed lunar lander. The crewed lander would have to land close to the unmanned return ship (at least within drving distance of the rover,) and the crew would change ships prior to the end of the lunar stay.
Option 2 would go well beyond being the "Barry Bonds" of "Apollo on Steroids." Think of it as Hulk Hogan and Macho Man Randy Savage, put together. It's definitely overkill, and you're not going to get an economy of scale by merely doubling the Ares 5 flight rate. Still, I think that option 2 would be enough to get Robert Zubrin to jump for joy.
Regardless of which option is chosen, I want my methane propulsion back on the CEV and both stages of the LSAM (which only had it on stage 2 in the original plan.) I think that any storability issues can be solved, and it will definitely give the lunar ships a kick in the pants, as far as Isp goes.
[EDIT 13 Apr 06] I am obligated to post that NASA Spaceflight has retracted its story
about the hard choices facing the lunar return mission. There is still hope that NASA can make "Apollo on Steriods" work within a reasonable budget and timetable without significantly diminishing capabilities.
Nevertheless, I still favor an L1 architecture, multiple assembly flights on smaller rockets (Atlas V 502, Delta IV Medium, or Ares I will all be acceptable,) and methane propulsion to the maximum practical degree. Even if ESAS proves to be technically possible, I still view it as a fiscally-flawed means of putting humans back on the moon.