What's up with Ares? 1

[genomon]

Just read another grim reaper article about the new Ares booster being so prone to severe vibration it may never become man-rated. Anyone hear any good news about it recently?

 

[GregLocock]

Sounds like the usual alarmism and silliness from non engineers. Saturn 5 started life rather ingloriously and ended up as everyone's favourite first stage.

Cheers

Greg Locock

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[GregLocock]

Here's the quote, doesn't sound very hard to fix does it "At a news conference in Utah, officials said the power unit for the nozzle controls, which steer a rocket in flight, was robbed of fuel, apparently because of a faulty valve."



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[btrueblood]

That's recent news, Greg. The pressure oscillation problem is fairly old news, see

http://www.spaceref.com/news/viewnews.html?id=1244

 

[GregLocock]

Oh OK, well vibration isolation is not an unknown mechanical engineering concept in the low tech industries.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[btrueblood]

Yup, a couple of tuned mass dampers, and presto, ready to go.

 

[GregLocock]

well, i was thinking of vibration isolators between the hot bit and the cold bit!



Cheers

Greg Locock

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[jistre]

Agreed with Greg. The F1 engines on the Saturn V's first stage originally had a pesky habit of going all explodey early on. This makes for a bad day for anyone sitting on top of one. The engineers slogged through it, got it fixed, and went to the moon. I'm confident that this, too, will be fixed.

 

[GregLocock]

Big difference being these are solid fuel of course, which makes it rather irritating to tune the acoustics - the organ pipe keeps getting longer and longer as the fuel burns, so the probaibilty of hitting trouble is much greater compared with a fixed geometry nozzle.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[btrueblood]

Err...actually Greg, the fuel burns from inside to out, the inside being a star shape so that the burning surface area stays more or less constant as fuel depletes. The organ pipe gets effectively bigger in diameter as the flight progresses, but the length stays the same.

What is tough is that have lengthened the SRB, relative to the shuttle SRB, by one segment or so, so in addition to lowering the organ-pipe resonant frequency, the longer length de-tuned whatever dead space (I think is was near the nozzle) they had left as a damper. Yes, they can fairly easily re-tune that dead space to damp the longitudinal mode, but it will probably require increasing the length (and thus dead weight) of the motor. Also, knowing whether the fix works or not requires more firing tests, which are expensive and take time. Apparently, the tuned mass damper is an option too - see

http://www.nasaspaceflight.com/2008...llation-mitigation-the-current-state-of-play/

FWIW, I worked at Rocketdyne in the early '80's and had the opportunity to discuss the F1 engine's stability with a few of its original designers. The big secret about that engine is it was never really fully stabilized (ok, that's an arguable point, I know, but I'm talking about verbal opinions here, not press-ready official NASA statements) ...it was just made more stable than its initial design (although, describing stability for rocket engines is not exactly a science either). They did also build a few extra 10th's of an inch of copper on the injector faceplate, so that the erosion that occurred there during firing (attributed to a swirling/spinning 1st tangential mode oscillation) wouldn't have a chance to fully burn thru the injector face before the mission duration was up...plus a little extra for margin.

 

[GregLocock]

They burn from inside out-Dang, I knew that once. Otherwise the tube burns up.

Cheers

Greg Locock

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[RobWard]

How are they ignited?
I magine that it's pretty important that both boosters fir simultaneously along their length.
(Light the blue touchpaper and run like billy-o?)

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[btrueblood]

"How are they ignited?"

Big roman candle throwing flame and sparks down the center hole. See

http://yarchive.net/space/shuttle/srb_ignite.htm

for a good quick description.

"Imagine that it's pretty important that both boosters fire simultaneously along their length."

Yes. One of the reasons for going away from a multi-motor rocket for the Ares, as the failure mode (one motor failing on ignition) is not recoverable (loss of vehicle and crew) for the Shuttle. Having an escape tower/rocket pod for the crew capsule is another "new" feature for the Ares.

 

[GregLocock]

Let's see, gas temp is probably 3000 K, so speed of sound is 1000 m/s, length of fuel section in booster is about 25m so that'd be around 20 Hz for the fundamental, certainly in the ballpark of the 25 Hz mentioned earlier.


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[RobWard]

Thank you btrueblood. Very interesting that!

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[GregLocock]

They are looking at -15 dB from the passive isolation system, and -12 dB from the TMD.

Both of those numbers are possible in SIMPLE systems. Rather excitingly they are turning a single degree of freedom system into a 3 DOF one.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[YoungTurk]

Anyone hear any good news about it recently?

Apparently successful full duration test Thursday. No mention of problems.

Press release.

Link with much cooler pictures:

http://www.spaceflightnow.com/news/n0909/10ares1/

 

[monkeydog]

Video of the test fire.

http://www.youtube.com/watch?v=rsPnkJ5vLfc&feature=player_embedded#t=31