CEV Design Q&A Options

[nprev]

Starting this thread in hopes that we'll all have some detailed insight into the next generation of MSF engineering.

Noble goal, eh? Truth of the matter is that I was just looking at one of the innumerable 'CEV enroute to the moon' artist conceptions, and I realized that the solar arrays as depicted meant that the vehicle almost certainly has to remain in a fixed attitude with respect to the Sun for them to operate at maximum efficiency. IIRC, the Apollos had to spin a bit in order to maintain thermal equilibrium & avoid localized heating and/or freezing.

Am I missing something here in terms of trade-offs? Seems unwieldy at best to have the arrays mounted to a sort of slip-ring assembly (with mast articulation) to maintain solar lock while the main body rotates. Likewise, seems as if an extensive--and in terms of power & volatile requirements/risk, expensive--ECS would be needed to avoid the temperature differential problem if the S/C is intended to maintain a continuous power-positive attitude during transit.

Sure that there's a simple answer I've missed; would very much like to hear it! (Let me guess: LOTS of heat pipes?)

[nprev]

Apparently, a significant resonant vibration issue has been discovered with the Ares first stage; the resolution should be interesting.

[ugordan]

From what I've read on nasaspaceflight.com this issue is a very serious one and untrivial to resolve. Without any dampening applied, the crew would experience longitudinal G force oscillations far beyond anything experienced till now and far above NASA recommendations on human safety. The vibrations would adversely affect both the Orion spacecraft and the cryogenic Ares I second stage, too. Any dampening mechanism would likely add significant weight penalties, even more so if you were to put it between the SRB and second stage (instead of between 2nd stage and Orion) to protect that stage as well.

I never could get my head around the reasoning of making a 5-segment SRB the base of a man-rated vehicle when SRB's are known to provide a very bumpy ride and cannot be shut down. SRB vibrations in itself have been a known issue ever since first solid boosters were developed (there are apparently two vibration modes, each due to different factors) so it's a bit funny no one figured out until now they might be problematic for an inline configuration, especially with the uprated booster. Just like (in retrospect) the shuttle payload configuration looks like a wrong design decision, this too looks to me like a bad choice.

The vibration problem should not affect the Ares V because the vibrations are dampened by "tying" two SRBs through the intertank structure, just as the Shuttle currently works.

[nprev]

SRB vibrations in itself have been a known issue ever since first solid boosters were developed (there are apparently two vibration modes, each due to different factors) so it's a bit funny no one figured out until now they might be problematic for an inline configuration, especially with the uprated booster.

I'm not too surprised, frankly; projectitis is endemic in government nowadays, and large issues seem to be discovered later rather then sooner. Still, despite that cheap shot on my part, at least they realized this seven years before the planned first launch. Based on the problem description, I speculate that they might be looking at an exhaust bell redesign of some sort to minimize the vibes, but this might be too simplistic from what you were saying, Gordan.

In analogy to aircraft, perhaps a stability augmentation system (SAS) would be a good answer, using vanes in the exhaust flow to disrupt the resonance. The problematic flight phase is just the first few minutes of flight; might be worth sacrificing some thrust for vibe dampening.