It shouldn't be overlooked that some of the engineers are still arguing for active TMA. If they're in favor of making a system more complicated, then the confidence level is clearly marginal, but this is the most favorable article I've seen in a while.
and used for Ares V as well (TO could be an issue on crewed Ares V).
Quote from: JIS on 12/10/2008 12:32 PMand used for Ares V as well (TO could be an issue on crewed Ares V). It wouldn't be an issue for Ares V because the SRB attachment to the core. Much like the shuttle doesn't have TO issues
Worth remembering that many people were opposed to Ares-I development even when it didn't suffer TO problems. Chiefly because it could be seen as a waste of time, money, and effort, achieving a goal that can be done with an EELV (or Jupiter). Blah blah....
Quote from: Jim on 12/10/2008 12:43 PMQuote from: JIS on 12/10/2008 12:32 PMand used for Ares V as well (TO could be an issue on crewed Ares V). It wouldn't be an issue for Ares V because the SRB attachment to the core. Much like the shuttle doesn't have TO issuesThis is a bit of a derailment, so I'll try not to make a big deal about it here, but I have to disagree with that statement completely. TO is a system resonance. The shuttle is a completely different resonant system than either Ares V (or Direct). There is no proof that I have seen (i.e. a detailed Finite Element Model) which says that either Ares V (or Direct) will not have a resonant axial mode around 12 Hz. I know it is a stretch, and I will admit I think it is highly unlikely, but TO could certainly be an issue for ANY in-line LV.And although the shuttle has no TO issues, it was my impression that the crew have felt TO before (they have felt stud hang ups - which are more benign IMO).
Ares I won't survive the first 100 days of the new administration, so no need to comment.
Good article. Don't expect to be hearing much from the EELV folks on this thread.
two tons mass dampers and what do you get, lot less payload and deeper in debt..
Quote from: iamlucky13 on 12/09/2008 06:27 PMIt's definitely surprising me, and I'm having a hard processing it. Resonant burning occurs every flight, correct? Why every flight ? Here are my attempts at defining variation factors:1/ Slag accumulation arround the submerged nozzleThe SRM nozzle is submerged, it protrudes inside the casing (for thrust vectoring purposes.) Hot molten aluminium oxides in liquid phase, a.k.a. slag, get trapped in the volume defined by the nozzle and the casing. This is not necessarily deterministic, not to the split second and not to the fraction of an inch.The cavity arround the nozzle is playing a role in the start of major pressure oscillations, in other words a role in the precise frequency, intensity, timing of TO.2/ Burn rate variations, due to minute batch variations, the day of flight/test temperature of the solid propellant, and a zillion other factors.It is the same thing as with POGO. Probabilistic. Different every flight, every test. 4-seg has probabilistic TO, 5-seg the same. IMO of course.
It's definitely surprising me, and I'm having a hard processing it. Resonant burning occurs every flight, correct?
...Every strap-on SRB in use, including the very large Shuttle and Titan SRB's, has been attached to the booster using a joint which is specifically designed to either safely absorb the forces of the SRB's oscillations, or to change the frequencies so that the TO frequency doesn't coincide with the resonant frequency of the vehicle any longer....The Ares-I doesn't have that option because both the Upper Stage and the Interstage must be hard-bolted straight onto the top of the SRB, and that location is proving to be an extremely tricky one to incorporate any such mitigation options into the design. This means that new techniques are required to fix the TO problems on Ares-I and that adds major development costs to a program already tight on budget. The heavier budget impact, combined with the longer DDT&E schedule only means that the programs implementation ultimately gets delayed even further.Result: Higher cost. Longer delays. Lower performance.Way to go.Ross.
I tell you Blazotron...I really like your posts. I get a good 'feel' from the technical side of things in that you explain it well (at least to me). The little things like dull tool cutters is something I never fully took to heart as an engineer-wannabe, that I now see your point about 1:3 & 3 (or 6) sigma situations.Obviously a good number of us realize we are getting never before behind-the-scenes opportunities as to the develomental phases of this new rocket (Ares-I). And we certainly do a fair bit of criticizing for armchair engineers (or wannabes as it were). But again, this is a give-and-take, and a learn as you go system. Relying on the information presented to us is only bringing rise to the answers or decisions we present on this forum. It is FANTASTIC that we can follow along as they make these designs & decisions. But as non-engineers (those among us) you have to expect a certain level of naiivitae when it somes to understanding the whole system. Guys (and gals) like you out there help us make better and more informed decisions. We appreciate all the feedback we get (I know I do), and from there we learn and grow and become better observers ( or critics)
So does anyone know about TO effects on Ariane 5... since it is somewhat similar to the Direct configuration: 2 SRBs attached to a central in-line core. Or are its SRB's less subject to TO?
Further, we only need to look at how long it took for TO to start being recognized as a problem on the structurally comparatively simpler Ares I design to realize that it isn't easy to dismiss it.
Quibble: what do you say to those who have posted here that TO was recognized as a potential show-stopper as soon as the VSE concepts were announced and had their concerns basically hand-waved away until it became clear how much of a Rube Goldberg solution might be required to mitigate it?
...My point in this post is that engineering is messy. Compromise is always necessary. Things are never as simple as they look at first. You never end up with the best solution--only one that is good enough.....
Quote from: blazotron on 12/10/2008 08:43 PMFurther, we only need to look at how long it took for TO to start being recognized as a problem on the structurally comparatively simpler Ares I design to realize that it isn't easy to dismiss it.Quibble: what do you say to those who have posted here that TO was recognized as a potential show-stopper as soon as the VSE concepts were announced and had their concerns basically hand-waved away until it became clear how much of a Rube Goldberg solution might be required to mitigate it?
Let's face it: Ares I with all the TO mitigation strategies that have been considered (plus all the weight scrubs it has forced onto Orion) is NOT anything close to what an objective rocket designer would have started from. It has turned to be neither "simple" nor "soon."
In ESAS and until last Spring, the Ares—I injected the Orion into a 30x160nmi transfer orbit and the Orion then circularized itself, to avoid the complexity of deorbiting the large upperstage. Working with Constellation and CEV project teams, the program elected to change to a -30x100nmi orbit to move the ocean impact of the CLV upperstage to the Indian Ocean from the South Pacific to stay away from populated islands.