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Chris Bergin
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« on: 08/18/2008 03:44 PM » |
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Worth a thread on its own as we'll be aiming to transcribe this event.
NASA to Brief Media About Ares I Thrust Oscillation Plans
NASA will host a media teleconference on Tuesday, Aug. 19, at 11:30 a.m. EDT, to discuss results and recommendations from the Ares I thrust oscillation focus team. The team has been studying possible solutions to concerns raised about the early designs of the new crew launch vehicle that NASA's Constellation Program is building to return humans to the moon by 2020.
The briefing participants are:
-- Jeff Hanley, manager, Constellation Program, NASA's Johnson Space Center, Houston
-- Steve Cook, manager, Ares Projects, NASA's Marshall Space Flight Center, Huntsville, Ala.
-- Garry Lyles, associate director for technical management, NASA's Marshall Space Flight Center
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« on: 08/18/2008 03:44 PM » |
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EE Scott
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« Reply #1 on: 08/18/2008 05:32 PM » |
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I can see it now: 1) here were the options being considered, 2) our great engineers have chosen the following solution(s), 3) no more need to worry, go about your business, nothing to see here....
OK, I am probably being too cynical.
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bobthemonkey
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« Reply #2 on: 08/18/2008 05:33 PM » |
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So 4.30pm BST, Chris?
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Chris Bergin
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« Reply #3 on: 08/18/2008 05:49 PM » |
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So 4.30pm BST, Chris?
Yep indeedy. Depending on permissions/L2, I *may* have an article on site surrounding this teleconference 
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bobthemonkey
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« Reply #4 on: 08/18/2008 06:25 PM » |
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Lovely. Won't be able to listen in live on this one, so thanks in advance to the transcribing hamsters.
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JRThro
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« Reply #5 on: 08/18/2008 08:27 PM » |
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I can see it now: 1) here were the options being considered, 2) our great engineers have chosen the following solution(s), 3) no more need to worry, go about your business, nothing to see here....
OK, I am probably being too cynical.
That's pretty much what I'm expecting, so if you're being too cynical, you're not the only one.
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Chris Bergin
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« Reply #6 on: 08/19/2008 03:05 PM » |
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Starts in 30 minutes.
We'll run our article later on today (would be arrogant to run it before they've had their say on the teleconference). Plus we'll have images of the three migitation options to be used together (Aft skirt, interstage and Orion) for our article - as per Plan A - which is going through to further maturity at the end of the year. They also have three Plan incorrect.
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Chris Bergin
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« Reply #7 on: 08/19/2008 03:32 PM » |
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Starting....
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Syntax
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« Reply #8 on: 08/19/2008 03:35 PM » |
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Is it not show on NASA TV?
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Chris Bergin
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« Reply #9 on: 08/19/2008 03:36 PM » |
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Hanley:
TO is the key technical issue over the last year with Ares I. Expresses his appreciation to the team on working the issue.
Cook: We have a created set of options. The good news here is we have a solution here to solve TO. Minimum impact to Orion. Allows us to dial up on unknowns. We have some upcoming tests to understand the human performance and STS DTOs.
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Chris Bergin
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« Reply #10 on: 08/19/2008 03:41 PM » |
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They are talking like they have TO solved!
TO happens at 115 seconds for a very few seconds. Dealing with crew performance during that time, to read console displays and respond to what they see.
The crew health issue is easy to mitigate. 1/4 G is the aim to reduce the TO.
Narrowband frequency - which means it is easily mitigated, and gave us a lot of options.
Made primary reccomendations. Can we go to the source, and make some changes (internal SRB). Can we move the acoustic modes? And we looked at cancelling the modes.
TMA - Parasorber option...but we decided to go with this at the aft skirt (TMA).
We found that there may be modifications to the inert systems, not the prop systems. We need to do cold flow tests for that.
So the mitigation options are separate from the mods to the motor.
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Chris Bergin
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« Reply #11 on: 08/19/2008 03:47 PM » |
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Passive systems work to mitigate the health limit to the crew.
Active systems - like active TMA are very effective with dealing with the frequency ranges to below 1/4 G.
Brought in additional people, such as KSC, to make sure there's no hazards, and relibility. We think we can make a sound reccomendation to the program.
Design changes to Ares only. Active systems allow us to make changes with uncertainty. There's a lot of immaturity with the vehicle, but the options are robust, flexible and tunable.
We can remove some of this options as we go and tune them as we move forward.
Two options combine. Detune damper in interstage. Active TMA in the aft skirt. (Not mentioning crew seats!!)
We believe this system will be reliable. Sixteen actuators in the aft skiry with batteries. But we can lose multiple actuators and still deal with TO.
We can design this system that if we lose the whole system. As a passive TMA, it will still be well under the health limits of the crew.
Loss mass on the concepts. Mass impact is 1,200 to 1,400lbs - which is within the mass margins for Ares I. We think we can go forward with this for the PDR.
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Chris Bergin
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« Reply #12 on: 08/19/2008 03:50 PM » |
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Keith Cowing gets the first question  Asks about alternative launch studies. Are you not looking at alternative studies... Cook: No, we are completely commited to Ares I. Options we have looked at are flight test vehicles. We have looked at concepts that would be transitional vehicles for Ares I. Over the last two to three years, we have not looked at alternative vehicles to Ares I and Ares V. We have never looked at EELV. The results of those studies are clear in the ESAS that Ares I/V is the vehicle of choice. Hanley re-states ESAS.
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Chris Bergin
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« Reply #13 on: 08/19/2008 03:52 PM » |
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We had legimate questions about Ares, but we have only responded to these questions - on alternate concepts.
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Chris Bergin
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« Reply #14 on: 08/19/2008 03:55 PM » |
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Bill Harwood asking about the TMA (well have an image of it in our article btw). "It's like the shock absorbers in your car."
"We are actually flying systems like this on other spacecraft to damper the payload from the vehicle".
"It's basically springs and dampers".
"If you can vision a cylinder, with a mass in the middle of it, with springs at either side" on describing the TMA. "The motor is attached to the mass, it moves the mass when it senses the vibration and react."
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Chris Bergin
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« Reply #15 on: 08/19/2008 03:57 PM » |
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Harwood on getting data from Ares I-X:
"We've asked and worked with the project to get vehicle accelarations and samples. We know the accoustics very well on the four seg motor.
"We'll also get data off STS-126. We're operating on ground test data and models. Ares I-X and 126 will be key data."
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Chris Bergin
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« Reply #16 on: 08/19/2008 03:59 PM » |
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AP question their mass figures on the TMA.
Notes a factor of 10 on payload to orbit.
"Performance margins are robust. We have 8,000lbs of margin" (we'll check that against their actual documentation - cause it sure ain't 8,000lbs).
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Chris Bergin
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« Reply #17 on: 08/19/2008 04:03 PM » |
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Fluff questions coming in, so let's see where we are.
TMA and interstage springs - but no mention of the crew seat pallet requirement.
Lots and lots of margin, claimed.
Seems like this is all aimed to get through the PDR.
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Chris Bergin
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« Reply #18 on: 08/19/2008 04:08 PM » |
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Ah, Todd H asks about crew seats. We decided at this point we don't want to put any more mass on Lunar Orion (but you have all that margin! ). It's still on the table, but not the mainline plan. Ho ho.
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Chris Bergin
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« Reply #19 on: 08/19/2008 04:09 PM » |
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Looks like they are going to put some images of the TMA and the Interstage dampers on NASA.gov shortly, btw.
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Namechange User
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« Reply #20 on: 08/19/2008 04:09 PM » |
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I don't buy it's as great as they all claim. Hanley's words were chosen very carefully. CONSTELLATION Program is not looking at any alternatives....that one word can imply a lot and then later you here him clarify about responses to "stakeholders". There's more than they claim going on.
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AnalogMan
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« Reply #21 on: 08/19/2008 04:12 PM » |
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Chris Bergin
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« Reply #22 on: 08/19/2008 04:12 PM » |
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Mark Kirkman, cool "Without the mitigation what G would the crew see?" "5-6Gs on the crew without doing anything. If we just used the passive system in the interstage - it would be below 1G - active system to less than 1/4G". Mark asks about 8,000lbs reserve lunar vs ISS. Says Lunar is 7,700lbs.
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Chris Bergin
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« Reply #23 on: 08/19/2008 04:17 PM » |
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Astro Office had no vetos - on a question about dissent (my word).
"Nobody vetoed anything in this process."
"The crew was represented from the beginning. The crew likes this reccomendation as it's so robust. We've had very good agreement on the solutions."
"The crew office has been active literally since day one on the vehicle."
"We've had a lot of conversations around the requirements - on crew health limit and the operational limit.
"We had a lot of conversations around the operational limit.
"To date we have held to the 1/4G limit. Going forward, we'll get data from the centrifuge. We just don't know enough to make an engineering case to go above the 1/4 G limit."
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Chris Bergin
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« Reply #24 on: 08/19/2008 04:18 PM » |
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"7,700 lbs of reserve on the lunar Orion. TO mitigation will use up about 1,200lbs of that."
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Chris Bergin
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« Reply #25 on: 08/19/2008 04:20 PM » |
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Bloomberg get mixed up with "two" mass aborbers and "tuned" mass aborber.
Seems to be drawing to a close now.
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Chris Bergin
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« Reply #26 on: 08/19/2008 04:26 PM » |
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They admit that they wouldn't do the PDR if TO mitigation wasn't at this stage. That is very key if you want my opinion.
Question about how many items are in their risk matrix.
"We're left with a couple in the red zone. We'll be redoing the list when we come out of the PDR.
"Performance is coming down from red.
"Schedule for the J2-X. That's coming down (from red)."
"There's nothing on our list that is a major issue. Everything is typical for a vehicle development."
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Analyst
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« Reply #27 on: 08/19/2008 04:29 PM » |
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So everything is fine. Great. Didn't expect otherwise. [Danger: irony]
Analyst
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Chris Bergin
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« Reply #28 on: 08/19/2008 04:32 PM » |
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And the teleconference has ended.
Post your *informed* opinions on this thread, as we create our article from their own documentation.
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GimmeSpace
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« Reply #29 on: 08/19/2008 04:35 PM » |
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Chris, thanks for the live updates, very cool..
With the first crew going up in 5 years or more, I really don't see this as a show stopper.
Call me a dumb newbie if you want, I'm still not buying the doom and gloom...
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Chris Bergin
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« Reply #30 on: 08/19/2008 04:39 PM » |
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Chris, thanks for the live updates, very cool..
With the first crew going up in 5 years or more, I really don't see this as a show stopper.
Call me a dumb newbie if you want, I'm still not buying the doom and gloom...
That's what they are saying, yep. The issue is - and they did make comments to be fair - is this is only to get the vehicle through the PRD. It's a good plan, it'll - on paper - work, but the vehicle is too immature to know. The flight data they have doesn't exist yet (DTO on 126 onwards). Never been a proper 5 seg test fire on the ground even. This would be a huge misrepresentation for any media to claim this problem is solved.
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Chris Bergin
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« Reply #31 on: 08/19/2008 04:41 PM » |
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AP question their mass figures on the TMA.
"Performance margins are robust. We have 8,000lbs of margin" (we'll check that against their actual documentation - cause it sure ain't 8,000lbs).
Checked their latest documentation, Prior to TO migitation hardware being added. "As of early August 08, Ares I lift to transfer point (11 x 100 mile orbit) performance margin is down to 4606lbs. Additionally, management margin is down to another 3469lbs. So they are adding their management (emergancy) reserves to get close to the 8,000lbs figure? Might be what they meant when they said "between us we have..." and if so, they are a 1,000lbs off.
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GimmeSpace
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« Reply #32 on: 08/19/2008 04:44 PM » |
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Chris, thanks for the live updates, very cool..
With the first crew going up in 5 years or more, I really don't see this as a show stopper.
Call me a dumb newbie if you want, I'm still not buying the doom and gloom...
That's what they are saying, yep. The issue is - and they did make comments to be fair - is this is only to get the vehicle through the PRD. It's a good plan, it'll - on paper - work, but the vehicle is too immature to know. The flight data they have doesn't exist yet (DTO on 126 onwards). Never been a proper 5 seg test fire on the ground even.
This would be a huge misrepresentation for any media to claim this problem is solved.
There are a lot of long homework nights ahead, but a long time to get there. I think you nailed it. Get the concept through PDR and keep that focus team busy. Any hints of development on SRM internal design tricks in the future?
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EE Scott
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« Reply #33 on: 08/19/2008 04:55 PM » |
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But why should there be any long homework nights ahead? We are trying to build an approx 28mt LEO booster for darn sakes - there is no need to be chasing our tail like this. The doom and gloom is that all this effort is WASTED effort. We could design and build something much easier, quicker, safer and WAY more cheaply if we didn't have the awful Ares I design tied around our necks. We should be able to design, test and make operational this LV in our sleep. But why do things the easy way, when you can do them the hard way for 10x the outlay $$$?
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Jim
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« Reply #34 on: 08/19/2008 04:56 PM » |
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Any hints of development on SRM internal design tricks in the future?
No, because it doesn't fix the problem
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Namechange User
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« Reply #35 on: 08/19/2008 05:13 PM » |
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But why should there be any long homework nights ahead? We are trying to build an approx 28mt LEO booster for darn sakes - there is no need to be chasing our tail like this. The doom and gloom is that all this effort is WASTED effort. We could design and build something much easier, quicker, safer and WAY more cheaply if we didn't have the awful Ares I design tied around our necks. We should be able to design, test and make operational this LV in our sleep. But why do things the easy way, when you can do them the hard way for 10x the outlay $$$?
Amen brother! The hard development should be for systems to be used off-world and beyond LEO. Ares 1 continues to drain the budget affecting all other current elements of Constellation and some think well, they have 5 years to solve it. Again, that should be a BIG RED FLAG, it should not have taken nearly 10 years by the time Ares/Orion fly to field a system less capable than the one that is currently operational!
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wannamoonbase
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« Reply #37 on: 08/19/2008 06:04 PM » |
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OV-106, I agree. The Ares 1 launch vehicle should be the easiest component of the constellation infrastructure. If Ares 1 is this hard, imagine what Ares V or Altair is going to be like.
And you almost never hear about Orion which will actually carry the organic life forms into space. Just the booster that does 20% of the work.
Its madness and fails the smell test in more than one way.
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AnalogMan
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« Reply #38 on: 08/19/2008 06:33 PM » |
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Chris Bergin
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« Reply #40 on: 08/19/2008 07:03 PM » |
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Yep, we've got some different images/additional info etc. Will include what's useful.
Might go expansive on this article rather than rushing it out. Will be today.
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Hunt101
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« Reply #42 on: 08/19/2008 09:18 PM » |
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We have never looked at EELV. The results of those studies are clear in the ESAS that Ares I/V is the vehicle of choice.
Hanley re-states ESAS.
ESAS got it wrong.
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marsavian
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« Reply #43 on: 08/19/2008 09:35 PM » |
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550-650 Kg payload hit sounds like Ares I is safe from cancellation/replacement.
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renclod
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« Reply #44 on: 08/19/2008 10:18 PM » |
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http://www.nasa.gov/pdf/267605main_TOmitigation.pdf speakes volumes. No way 100 pounds x 16 is the counter oscillating mass. IMO the shaking mass is the aft half (2 rings) of the aft skirt. The upper 2 rings are bolted to the aft segment; the TVC actuators (to SRB nozzle) are connected to ring 2 (convention: ring 1 is forward, smaller; ring 4 aft, larger). Rings 3 and 4 are bolted together and this assembly is mobile on X axys (on "springs" and electromagnetic dampers) . Like I said in another thread, the internal TMA, parachutes assy is too light; half the aft skirt should be the "external" TMA (or "reaction mass"). Just my reading into this. Could be wrong.
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Chris Bergin
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« Reply #45 on: 08/19/2008 11:00 PM » |
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Interestingly (I'm still writing the article and speaking to engineers) there's two versions of this system and Plan A is the passive system (TOA). The battery system (RMA) is pretty much the same thing, but given you need crew seat isolators for the passive system, you will for the battery system too - as a failure mode. If the RMA fails and turns into passive, then they are at 1G and that's over their 0.25 limit. To give you an idea, Shuttle is 0.1G during First Stage.
Problem with the seat isolators is it won't be ready in time for the PDR....and they really want to get through the PDR without TO getting in the way.
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TRS717
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« Reply #46 on: 08/19/2008 11:10 PM » |
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Didn't they say in the presser that seat isolation system had been removed as unnecessary? They added that they didn't want to carry a system used for just a few seconds during ascent "all the way to the moon and back."
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marsavian
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« Reply #47 on: 08/19/2008 11:17 PM » |
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This is the B2 option. They said if the active part failed it would still be about 0.5G which was deemed acceptable for health. 1G was for the frustrum isolator alone.
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blazotron
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« Reply #48 on: 08/20/2008 12:06 AM » |
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http://www.nasa.gov/pdf/267605main_TOmitigation.pdf
speakes volumes. No way 100 pounds x 16 is the counter oscillating mass. IMO the shaking mass is the aft half (2 rings) of the aft skirt. The upper 2 rings are bolted to the aft segment; the TVC actuators (to SRB nozzle) are connected to ring 2 (convention: ring 1 is forward, smaller; ring 4 aft, larger). Rings 3 and 4 are bolted together and this assembly is mobile on X axys (on "springs" and electromagnetic dampers) .
Like I said in another thread, the internal TMA, parachutes assy is too light; half the aft skirt should be the "external" TMA (or "reaction mass").
Just my reading into this. Could be wrong.
My reading from the press conference was that the reaction masses were in fact about 100 lbs. It's important to remember, though, that you are talking about a tuned system. You don't need a reactive mass on par with the mass of the first stage, for instance. You just need to reduce the q-factor of the system ( http://en.wikipedia.org/wiki/Q_factor) enough that the forcing function (the vorticular structures in the engine) is ineffective at adding additional energy to the oscillating system, which in turn keeps the forcing function weak.
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Chris Bergin
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« Reply #49 on: 08/20/2008 12:08 AM » |
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This is the B2 option. They said if the active part failed it would still be about 0.5G which was deemed acceptable for health. 1G was for the frustrum isolator alone.
Sure is Plan B2. And those plans are just a week or so old, so I'm not sure why it's not listed as Plan A.
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Tim S
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« Reply #50 on: 08/20/2008 12:26 AM » |
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This is the B2 option. They said if the active part failed it would still be about 0.5G which was deemed acceptable for health. 1G was for the frustrum isolator alone.
Sure is Plan B2. And those plans are just a week or so old, so I'm not sure why it's not listed as Plan A.
Because Plan A with the crew seat isolators would not get through the PDR like the two other options. But this is all incredibly early days.
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iamlucky13
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« Reply #52 on: 08/20/2008 01:19 AM » |
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TO happens at 115 seconds for a very few seconds. That sounds awfully specific. I'd be curious how it's expected to rise and fall throughout the flight...for both Ares 1 and the shuttle. Several astronauts have described shuttle liftoff as involving intense shaking. Narrowband frequency - which means it is easily mitigated, and gave us a lot of options. I figured as much, but it's relieving to here it. This means that passive solutions can't wander from a damping effect into a disasterour resonant effect. We decided at this point we don't want to put any more mass on Lunar Orion (but you have all that margin! ). The 8000 pound margin on Ares 1 is for the first stage, as I understand it, meaning it can gain 8000 pounds of mass and still get the second stage to the point where it needs to be to meet its performance target. Also, a pound on the first stage hurts less than a pound on the second stage which hurts less than a pound on Orion. Any hints of development on SRM internal design tricks in the future? I thought this was a hint in that direction, but I could be wrong: We found that there may be modifications to the inert systems, not the prop systems. We need to do cold flow tests for that.
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kraisee
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« Reply #53 on: 08/20/2008 03:44 AM » |
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TO is a direct function of Thrust levels.
It's cumulative effect is a function of Thrust : Weight for the whole vehicle though.
As the solid propellant burns away the First Stage gets a *lot* lighter. The First Stage propellant represents almost 70% of the total vehicle mass at liftoff and that will all be burned away within ~2 minutes.
But the thrust levels do not tail off much through to about T+110 seconds - because the propellant burns from the inside towards the outside of the cylinder, there is actually a higher surface area to burn as the Stage gets closer to burnout.
You get a gradual increase in TO forces all the way through to about T+110 where it peaks (much lower vehicle mass, but still high thrust levels). It remains around the peak value for a handful of seconds and then trails off fairly quickly (~15-20 seconds) as the booster burns out.
By the time you have burned most of the solid propellant, the TO force remain the same (about 100,000psf), but the vehicle mass has dropped to ~30% of what it started out with. So the TO force is now acting at the equivalent of >300% more effect than it had at liftoff.
The "trouble zone" actually begins around T+90s (roughly 75% solid propellant burned already), but the TO peak isn't until 20s later.
Ross.
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iamlucky13
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« Reply #54 on: 08/20/2008 07:18 PM » |
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Thanks Ross. That's what I was kind of getting at, but I was confused by the paraphrased quote from the live coverage that said TO "occurs at 115 seconds" rather than peaks at it. You clarify it very well. http://www.nasa.gov/pdf/267605main_TOmitigation.pdf
speakes volumes. No way 100 pounds x 16 is the counter oscillating mass. By my math, 1600 pounds oscillating sinusoidally at 15 Hz can create a sinusoidal peak-to-peak force of 100,000 pounds if it has a total displacement of 2.7 inches. I picked that number based on the 100,000 mentioned by kraisee, although now I see that he said the TO force is 100,000 psf, not lbf. That's a discrepancy...is it force or pressure? 5-6 G's would suggest to me its the pressure, but 5-6 G's sounds way out of scale for a booster pulling 3-4 G's RMS (+/- 100% chamber pressure?)...err, I guess I'm forgetting about the 2nd stage resonance. The required displacement scales linearly with the required force. I'm not entirely sure how the power scales, but I think it's roughly to the square of the required force. It seems to me they're going to need some hefty, high draw batteries.
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kraisee
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« Reply #55 on: 08/20/2008 08:03 PM » |
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Sorry, lbf was what I meant.
The un-mitigated TO g-force (measured inside the CM) is apparently ~6.5g @ ~9Hz, with a second node ~4.5g @ ~12Hz.
Ross.
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renclod
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« Reply #56 on: 08/21/2008 09:27 AM » |
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How heavy was the parasorber ? The RSRB has 3 main parachutes x 2180 lb = 6540 lb. (The drogue is an additional 1200 lb but maybe the drogue was not included in the reaction mass). The RSRBV's main parachutes (so the parasorber) should be even heavier. Add to that some more for the entire assembly.
IIRC the parasorber was supposed to travel up to 8 inches.
Now we have 16 x (100 to 150) lb reaction mass = 1600 to 2400 lb. About 1/3 of the parasorber. And it's supposed to work to under 1g @ crew (together with the isolation plane, true) even if the control system fails - amazing.
Of course my speculation about the aft skirt is just that - speculation.
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iamlucky13
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« Reply #57 on: 08/21/2008 05:37 PM » |
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Hmm...interesting bit about the parasorber. I'm guessing, given that my numbers were fairly easy to generate, that the Ares 1 engineers went into a lot more detail before leaning towards the multiple TMA idea. Parasorber also has no redundancy. The other factor that comes to mind is that the parachute mounting and packaging might need significant rework to accomodate the parasorber concept that could be straining the schedule, pushing it to a backup option. I'm still boggled by the 6.5 G figure. As that TO peak approaches, the total mass of the stick should be somewhere on the order of 300,000 kg, and I'm guessing the thrust will still be up above 2 million pounds for the 5-segment( source). That gives 3 G of average thrust. A +/- 100,000 lbf thrust oscillation at that mass only accounts for +/- 0.15 G of accelleration. I'm also not clear on the zero point of that 6.5 G's...is it 3 +/- 6.5 (eek!), 3 +/- 3.25 (6.5 total), 3 to 6.5, etc.? The first requires an amplification ratio of about 40, which means nearly perfect coupling of the forcing frequency to the natural frequency of the stack. It almost seems freakishly unlikely to the point that if anyone less than NASA was saying it, I'd have trouble believing them.
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bad_astra
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« Reply #58 on: 08/21/2008 06:05 PM » |
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I'm not a structural engineer, so please everyone don't bite my head off but with the dampers being added into the mix, won't they have to take a tremendous amount of torsion, depending on what RCS is doing?
I know this is negative, but it seems like they'll do anything to make a rocket that vaguely looks like the initial CLV.
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iamlucky13
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« Reply #59 on: 08/21/2008 06:19 PM » |
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bad_astra, are you referring to the "softride" isolators between the 1st and second stages? Yes, those will see a load from the RCS, which I believe will be primarily bending, rather than torsional. Chris' article mentions that the bending loads during flight were a concern even without that feature, and the isolators increase the risk in that area. Also, I think your head is pretty safe when asking honest questions like that.
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Antares
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« Reply #60 on: 08/22/2008 05:50 AM » |
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The RoCS loads on the Softride buttresses (these things look Gothic to me) will be small compared to the rest. The bending loads are far worse.
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bad_astra
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« Reply #61 on: 08/22/2008 03:38 PM » |
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Perhaps if they had went with the lattice type interstage they could have incorporated the isolators into the framework.
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foltster
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« Reply #62 on: 08/22/2008 11:35 PM » |
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Thanks Ross. That's what I was kind of getting at, but I was confused by the paraphrased quote from the live coverage that said TO "occurs at 115 seconds" rather than peaks at it. You clarify it very well.
http://www.nasa.gov/pdf/267605main_TOmitigation.pdf
speakes volumes. No way 100 pounds x 16 is the counter oscillating mass.
By my math, 1600 pounds oscillating sinusoidally at 15 Hz can create a sinusoidal peak-to-peak force of 100,000 pounds if it has a total displacement of 2.7 inches.
I picked that number based on the 100,000 mentioned by kraisee, although now I see that he said the TO force is 100,000 psf, not lbf. That's a discrepancy...is it force or pressure? 5-6 G's would suggest to me its the pressure, but 5-6 G's sounds way out of scale for a booster pulling 3-4 G's RMS (+/- 100% chamber pressure?)...err, I guess I'm forgetting about the 2nd stage resonance.
The required displacement scales linearly with the required force. I'm not entirely sure how the power scales, but I think it's roughly to the square of the required force. It seems to me they're going to need some hefty, high draw batteries.
Maybe they could use those heavy batteries as the oscillating mass???
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robertross
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« Reply #63 on: 08/25/2008 10:21 PM » |
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Batteries normally don't take too well to serious vibrations. If the battery shorts, there goes your TO mitigation method, plus a fire or explosion from the battery bursting. Plus the wiring, which is normally tied to brevent breakage, is whipped around like a skipping rope.
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phred
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« Reply #64 on: 09/07/2008 03:11 PM » |
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Has there been any specific information on how these oscillating mass actuators will work? I understand batteries will somehow drive mass back and forth, but what's the mechanism?
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kraisee
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« Reply #65 on: 09/07/2008 04:50 PM » |
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An electro-magnetic coil around a moving metal mass inside.
Although Chris has info on L2 right now talking about hydraulics... But you'll have to be an L2 subscriber to learn about that.
Ross.
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