Chair Force Engineer

Tuesday, May 19, 2009

Amateurs talk rocket tactics, professionals talk rocket logistics

The DIRECT rebuttal to NASA’s analysis of their concept includes some very telling observations of NASA’s mentality in creating and defending the existing infrastructure. Perhaps the most telling NASA observation comes on slide 64:

-More detail on Launch Infrastructure than on vehicle design.

--This is a design that is sized by infrastructure as they note in their paper.

--However to date Launch Infrastructure is not on the critical path of Ares-V or Ares-I

To which DIRECT responds by saying:

-The fact that the infrastructure is not being considered by Ares is one of the reasons why that architecture costs as much as it does.

--Cost of all supporting systems, not just infrastructure must be one of the many factors considered as part of the critical path.

All I can say in response is “Wow.” Are we to believe that ESAS was designed with little or no consideration of what the supporting infrastructure would cost? It would certainly explain why we’re stuck with the unaffordable Ares I and Ares V.

Further NASA statements such as “Ares I + Ares V uses 15 SRB segments, while two Jupiter 232’s use 16 segments” also reveal an incredibly simplistic approach to cost estimation. Such simple methods might be appropriate for pre-algebra students. Professional cost estimators ought to know better. That's why cost estimation is so difficult; there may literally be thousands of dependent and independent variables that make up the true cost of the system over its lifetime. Saving a few million in rocket hardware may have bigger reprocussions with development dollars, standing army costs, and infrastructure costs. It’s best summed up on Slide 26, where Jupiter’s higher launch costs (measured in tens of millions per launch) are offset by the savings of billions in development costs.

The DIRECT rebuttal also points out a problem the EELV advocates have encountered. In estimating upper stage masses, NASA has become excessively reliant on software tools like INTROS, which give fairly high estimates for upper stage dry masses. When INTROS cannot match the values for real, flight-proven hardware (like the EELV upper stages,) it might be time to revise the INTROS code. If nothing else, NASA’s impartial estimators should defer to the real values of flight hardware when the numbers conflict with the computer estimates.

All-in-all, DIRECT appears to be a more affordable architecture for a shuttle-derived lunar transportation system. I say this as somebody who earned a BS in Aerospace Engineering and actually did some serious study of solid-rocket internal ballistics during senior design class, giving me a first-order feel for how lengthy a new SRB development program will be for ATK and NASA.

With that being said, DIRECT still faces an uphill battle against “the unknown unknowns.” How well will the Centaur balloon-tank structure scale up to the larger diameter of the Jupiter rockets? What new guidance and rendezvous techniques and docking systems are required to mate the Earth Departure Stage to the Altair-Orion stack once on-orbit? What other previously-unknown problems, such as SRB heating of the core engines, will affect DIRECT once development begins?

At this point, a swap of Ares for DIRECT will result in little net gain from a schedule or technical risk perspective. While Ares proponents might argue that the last four years have seen the design mature, Ares is still years away from flying significant flightworthy hardware. The maturity of Ares today is comparable to where DIRECT’s predecessor, National Launch System (aka New Launch System) was in 1991. The only potential crew launcher with any maturity is Delta IV Heavy. If SpaceX is lucky, Falcon IX will have a successful flight before the Augustine Commission completes its report.