Sunday, September 13, 2009

Dr. Griffin on the Augustine Committee - Part 9 of 11

9) The recommendation in favor of the dual-launch "Ares-5 Lite" approach as the baseline for lunar missions is difficult to understand. ... Because of the economies of scale inherent to the design of launch vehicles, such a vehicle should be designed to lift as large a payload as possible within the constraints of the facilities and infrastructure available to build and transport it. This provides the greatest marginal improvement in capability at the lowest marginal cost.

I don't have much to say about Ares 5 vs Ares 5 Lite. Neither option looks good to me. I can understand why the committee would look into Ares 5 Lite rather than Ares 5, simply because a single vehicle smaller than the larger of the Ares 1/Ares 5 pair is liable to be faster, easier and cheaper to develop. Let's face it - like it or not, development cost, schedule, and risk are the make-it-or-break-it issues at hand, not getting the greatest marginal improvement in capability at the lowest marginal cost during operation.

Griffin's approach of designing the biggest launcher possible ignores the tremendous cost and time penalty of doing the development. Simply put, Ares 5 may be too expensive to build, even if it is cheaper than Ares 5 Lite on a pound per pound basis. It also ignores the costs to maintain separate infrastructure for both Ares 1 and Ares 5.

Griffin's approach does not consider the benefits of a steady pace of frequent launches to lower marginal cost by spreading fixed costs over more launches, and by encouraging rocket construction that more closely resembles assembly line operations, and perhaps rocket operations that more closely resemble airline operations. Ares 5 would only launch a couple times per year, so it would certainly not benefit from these economic forces. A 2-launch Ares 5 Lite would benefit a bit more from the steady pace of launching the same rocket, but other alternatives could benefit from this force even more.

The real problem with Ares 5 is that it does not contribute to the real goal, which is not to deliver as much mass as possible to the lunar surface per year, per launch, or per dollar, but rather to lower the cost of U.S. launchers in the classes relevant to commercial space, security, and robotic science missions. Such an achievement can be the contribution of the VSE's launch component to the specific, fundamental VSE goal of "security, economic, and science" benefits. If serious commercial, security, and/or science interests step forward with requirements for Ares 5 or Ares 5 Lite launch, then of course we would be justified in taking another look at these rockets. As it is, Ares 5 and Ares 5 Lite don't contribute to the real goal of the VSE.

... All parties agree that a heavy-lift launcher is needed for any human space program beyond LEO. ...

The Augustine committee may support one sort of heavy-lift launcher or another, but I don't agree with them (or Griffin) in this case. First of all, most human space program architectures I've seen that seek to establish infrastructure and do work in GEO, Earth-Moon Lagrange points, and lunar orbit don't include a heavy-lift launcher at all. Typically they involve 1-3 launches of EELV-class payloads to establish some sort of space infrastructure (a servicing node, small space station, depot, etc), and 1-2 launches of EELV-class payloads to get astronauts to LEO and then to the destination (perhaps on an in-space only vehicle). It should be clear that these destinations - GEO, Earth-Moon Lagrange points, and lunar orbit - are all "human space programs beyond LEO". It should also be clear that there is plenty of useful work to do there, such as satellite servicing in GEO, satellite servicing at Earth-Moon Lagrange points (perhaps of Earth-Sun Lagrange point observatories that move themselves or are tugged between these points and the Earth-Moon points), lunar observations from lunar orbit, lunar telerobotics, and build-up of space infrastructure in these orbits and regions to enable greater exploration later.

None of this needs to involve either heavy lift or refueling.

Note that these missions are the type that are most likely to be achievable in anything like the near term, so these are the ones we should be planning for the most, and spending most of our attention on. Surface missions to Mars using 6 or 7 Ares 5 launches and an Ares 1 launch (as presented by NASA to the Augustine Committee) are so distant in time, and so absurd in their per-mission cost using available technology and infrastructure, that we shouldn't be concerned with developing a specific architecture or launch vehicle for them at all yet.

So, I disagree with the statement "a heavy-lift launcher is needed for any human space program beyond LEO."

By the time NASA has become proficient in GEO, lunar orbit, and Earth-Moon Lagrange missions, and it ready to pass these missions on the commercial space, refueling technology could have been demonstrated. With this capability, more destinations are within reach. Still no heavy-lift launcher is needed.

If refueling is not to your taste, add a much milder heavy-lift upgrade, such as a "Phase 1" EELV upgrade to the 40-50MT class, or a similar-sized giant SpaceX Falcon. This is considerably less powerful than the Augustine committee's smallest HLV, the "Phase 2" EELV 75MT class launcher. The development cost and risk should be correspondingly smaller. This class of "mini-HLV" is all that we should need by the time we achieve what we can in GEO, lunar orbit, and Earth-Moon Lagrange points, which will be a long time from now. The "Phase 1" EELV HLV in combination with the appropriate reusable space infrastructure and space assembly would allow us to achieve plenty.

There could come a time after this when a larger HLV is desired - but that time is so far off that we needn't concern ourselves with it. By then, the HLV question should be in the hands of the commercial space market anyway.

1 comment:

Roga said...

This series is very well argued, and I agree completely. Technically, you are spot on with recommendations of commercial crew to LEO, no obvious near-term need for an HLV and so on. But I especially like when you catch the politician in his own lies. Keep up the good work.