January 21, 2008
The Sound of Costs Overrunning
Posted by scott at January 21, 2008 08:58 AM
Having (for now) conquered Orion's critical weight problem, NASA must now conquer Ares I's predicted tendency to shake itself and its cargo to pieces. Because, you know, having the vehicle come apart around you would be bad.
Most likely this is a case of press-release journalism run amok. The thing is still almost literally on the drawing board, so changes are comparatively simple. I have no doubt they'll solve this one. Paying for it, well, that's a whole different issue altogether.
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It's funny. Fifty years on, and the press is still reporting rocket science in the same way.
"Ours always blow up! Our satellites never work! Our scientists can't get the job done! The Russians will beat us! The Chinese will beat us! We're doomed! DOOMED! DOOOOOOOOOOOMMMMMMMED!"
"Actually, we expected this problem and we know how to fix it. In fact, we just did, and now we're working on the next problem."
"Problem? PROBLEM! Ours always blow up! Our scientists can't get the job done! We're doomed! (etc.)"
It's definitely a bit over-reaction-ish. From what I could glean from the article, the problem is relatively simple: the propulsion pulses match the natural frequency of the combustion chamber. If that's the case, changing the frequency of the chamber or the propulsion rate is called for - out of sync = no shaking.
Simple to say, difficult to do. But that makes it an engineering problem - and engineers are pretty damned good at getting around stuff like this.
From what I could glean from the article, the problem is relatively simple: the propulsion pulses match the natural frequency of the combustion chamber.
As I understand it, the problem is a bit more serious. The problem is there's too much vibrational energy input near one of the resonant frequencies of the rocket as a whole (transverse vibration of the second stage with respect to the first). This will require either adding mass to change the frequency or adding mass to damp the vibrations. Neither option is particularly good.