Chair Force Engineer

Tuesday, September 26, 2006

Without a Trace

NASA recently made public the details of a 2009 "test flight" for the Ares I rocket, referred to as "Ares I-1." The big point of contention is the use of a standard shuttle SRB with a dummy fifth segment added between the SRB and the dummy upper stage. The test begs the question, how traceable are the results of this test towards the final Ares I?

To be fair, dummy upper stages used to be the way that rockets were incrementally tested. Saturn I flew its first few missions as the Block I with an inert upper stage. But it should also be noted that the Block I first stage was very similar to the Block II first stage, and the first stage of the Saturn IB that was to follow. Schedule expediencies led NASA to do away with incremental testing (which, for rockets like Falcon I, might have been a better idea than all-up testing.)

This Ares I-1 mission will unfortunately not have the degree of traceability to the final Ares I that I would like to see. The four-segment SRB of Ares I-1 will burn out around Mach 4, while the 5-segment SRB should reach Mach 6. The nozzle design for Ares I-1 will probably be the same as the original shuttle SRB, and the parachutes will be unchanged too.

I won't say that the test is a total throwaway. The aerodynamics, structure, avionics and control systems will be largely validated through this test. The Ares I-1 will probably pass through Max-Q with similar results to the real Ares I. Still, I don't see why NASA can't wait for the 5-segment SRB to go through a few static firings and use that instead. Rushing ahead with a test using the 4-segment booster (when your real desire is to fly the 5-segment booster) is just Faster, Cheaper, and Crappier.