Chair Force Engineer

Thursday, January 15, 2009

Boundary Conditions

The staff of LaunchSpace wants everybody who cares about the fate of Project Constellation to keep quiet and let the big boys at NASA get on with business of going back to the moon. It's a nice sentiment, if you buy into the belief that NASA is nigh-infallible and that their plan will get us back to the moon with a reasonable amount of time and money.

At the same time, the most visible of the alternatives to Project Constellation is getting exposure in Popular Mechanics and even got a meeting with the Obama transition team. The promoters of DIRECT may see the change in administrations as their best (and perhaps final) chance to salvage Project Constellation from the budget and schedule nightmares that lie ahead.

We have a situation where multiple groups all believe they have the best solution to the challenge of going back to the moon. For what it's worth, twelve industry contractors submitted Crew Exploration & Refinement studies in Fall 2004, and their results were drastically different from either DIRECT or the NASA baseline.

How could fourteen different studies result in fourteen different conclusions about the best way to go back to the moon? The answer can simply be summed up as a difference in assumptions and evaluation criteria for what is truly best. How big of a crew are you sending to the moon? How many days will the mission last? What sites on the lunar surface will be accessible? How much volume does each crew member need in the capsule?

The criteria and assumptions that went into the ESAS study of Summer 2005 have been widely and justifiably criticised. The expendible SSME and air-start SSME which formed the basis of the early Ares designs were unrealistic. It was assumed that the existing Atlas and Delta rockets could not tailor their trajectories to enable aborts during all flight phases. On-orbit assembly and orbital refueling were viewed as highly undesirable, at best. It's enough to make one wonder what other flawed assumptions and judgement criteria went into the study.

While Ross Tierney relied on post-Challenger design studies for his original “DIRECT 1.0” concept, it should be noted that the Jupiter design was independently validated by Stephen Metschan using his FrameWork CT optimization software. FrameWork CT evaluated numerous configurations in a fashion similar to ESAS, but with different ground rules and assumptions. Neither approach is perfect, but I’m inclined to believe that ESAS is heavily flawed based on its low-balling of the cost for the five-segment SRB and other invalid assumptions.

The subjectivity of evaluation criteria is clear from the simple question whether Ares I is safer than Jupiter 120. The answer is conceivably yes, because it has less engines. But Jupiter 120 mitigates this by lighting both RS-68’s on the ground prior to igniting the SRB’s (which have an incredibly reliable ignition system.) Jupiter 120 gives you the confidence that all engines have been tested at liftoff. By contrast, Ares I relies on a staging event in which you hope and pray your second-stage engine ignites. Additionally, Jupiter 120 has more performance, allowing for greater redundancy to be added to the Orion capsule. This is the area where evaluators have to look at the probability of a staging failure on Ares I versus a loss of engines early in the Jupiter 120's ascent, or the probability that extra redundancy in certain capsule systems will allow the crew to survive in an emergency scenario. The analysis of these probabilities, and the weights given to predicted reliability numbers, present plenty of room for the experts to debate until they are blue in the face.

Every design will also possess unintended consequences that must be worked out once it has been chosen. Prediction of these consequences is a reflection of how valid and effective the original design trade was. For Ares I, launch drift and thrust oscillation are the challenges that we’ve bought. Jupiter would certainly have its own challenges, although it’s hard to see them being worse than launch drift or thrust oscillation.

I would like for the next NASA Administrator to call time-out and order a re-evaluation of crew and cargo launch strategies that takes development costs into account with infrastructure and operational costs for the expected duration of Project Constellation (from now until at least 2025.) The agency should look at permutations of all realistic crew launch & cargo launch designs. Examine Ares I, Jupiter 120, Atlas V Heavy, Delta IV Heavy, and Wide-Body Atlas for crew launch. Take a gander at Ares V, Jupiter 232, and a side-mount Shuttle Derived Vehicle similar to Shuttle-C. Take a realistic look at the assumptions which are driving the Orion capsule weight (especially the amount of volume available to each crew member) and the number of man-days the Altair lander is expected to support on the lunar surface.