The Incredible Shrinking Orion
1. Acceleration of Ares & Orion
2. Cancellation of Ares I while retaining Ares V
3. Shrinking Orion to fit on an Atlas V or Delta IV
4. Shrinking Orion to fit on a foreign launcher (H-2A or Ariane 5)
5. Accelerate COTS-D (SpaceX Dragon, perhaps other vehicles)
Before discussing any of these options, it's worth asking the question of how big Orion needs to be in the first place. While the ESAS report cited 22.5 tonnes and a diameter of 5.5 meters (later reduced to 5 meters,) there is no discussion of exactly how much volume a crew needs for a lunar mission, and the diameter seems to be an arbitrary number with zero justification. My preference is to look at historical examples (chiefly, Apollo,) and use that to determine the requirements for the next manned spacecraft.
The Apollo capsule had a diameter of 3.9 meters and afforded a 3-man crew an adequate amount of room for a two-week lunar voyage. That same volume was adequate to deliver a crew of five or six on a shorter trip to Skylab (as studied during the Skylab rescue planning and the shuttle escape study.) For earth-orbit missions, Apollo weighed as little as 14.7 tonnes. For lunar missions, the additional consumables and propellant brought that weight to 30 tonnes. Apollo also required nearly seven years to move from contract award to first manned flight.
In ESAS, NASA dismissed the stock Atlas and Delta on the grounds of crew safety during mission aborts. While those fears were shown to be spurious during the Atlas man-rating study performed by Lockheed Martin, the performance of both rockets leaves much to be desired. NASA should budget no less than 30 tonnes for Orion. While the new spacecraft won't need propellant to perform a lunar-orbit insertion burn, and it trades the mass of fuel cells for lighter solar arrays, the capsule will need to be heavier to accomodate a larger crew, and the spacecraft will have to carry more consumables.
If Orion shrinks to the point where it can fly on an existing launcher, the lunar goal will be deferred or cancelled entirely. Perhaps a two-man Orion would be light enough to launch on an EELV and still be capable of a lunar journey, at the expense of higher crew workload and diminished science return from a lunar sortie.
Most disturbingly, if Orion is limited to earth-orbit missions, it destroys the rationale for Dragon and COTS-D. What incentive will NASA have to buy commercial launches for ISS if Orion does the job? While Bob Bigelow's space hotel plans might give SpaceX some incentive, the real near-term prize is COTS-D. The chicken-and-egg dilemma here is that a COTS-type vehicle must be ready before the Bigelow space hotel can go into operation.
Getting back to the meat of the post, I wanted to take a quick look at the four scenarios being examined by the Obama transition team:
1. Acceleration would be difficult to achieve with the existing Ares and Orion vehicles. It may have to come at the expense of testing, which is rarely a sound strategy (except in the case of all-up testing in Apollo.) Based on the 2006 contract award for Orion and a seven-year development time, we can't expect the capsule to be ready for manned flight any sooner than early 2013. That figure is optimistic, assuming that Orion is at a similar level of completion to where Apollo was in early 1964. An infusion of added cash into Ares and Orion will probably not accelerate the schedule; rather, they will serve to prevent the schedule from slipping further to the right as unanticipated problems rear their ugly heads.
2. This is my favored option, when paired with #5. Ares I will take too long to develop and has no real chance of closing the gap. Ares V and Orion can be kept going as a jobs-retention program. Perhaps NASA can adopt a two-Ares V mission profile, avoiding the tight mass margins currently encountered by the current architecture.
3. Again, I think there's nothing to be gained by stripping Orion down to the point where it can no longer perform a practical, safe lunar mission. The EELV option should be a non-starter.
4. The foreign launchers option is an interesting one, even though it suffers the same flaws as the Atlas/Delta option. It's interesting to note that Ariane 5 was designed with a manned spacecraft (the Hermes spaceplane) in mind. Even if the foreign boosters had the performance required to lift Orion in its current form, I think that "not invented here" and jobs-retention issues will scuttle the idea.
5. As many NewSpacers have pointed out before, the most cost-effective use of manned spaceflight dollars would be cancelling Ares I and using the savings to fund the unfunded COTS-D program. If I were advising the president-elect, this is exactly the advice I'd give him. An accelerated Dragon program gives America the best shot to have a manned spacecraft flying by 2012 or 2013.
I'd also recommend keeping Orion, Altair and Ares V going at a slower schedule and a lower spending profile until "the gap" was closed. At that point, a decision could be made on whether to proceed with manned lunar missions. NASA could retain "Apollo on Steroids" using two Ares V's per mission, or an "Apollo Redux" which would perform a more limited mission with a single Ares V launch.