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Space Forum / Shuttle / February 2008Ares 1 - "Pencil-Pogo"?
Will the Pencil suffer from Pogo Effect due to the long-thin design and the use of the SRB? > Will the Pencil suffer from Pogo Effect due to the long-thin design and the > use of the SRB? Solid motors don't get pogo On Feb 26, 6:53 pm, behlin...@gmail.com wrote: > > Will the Pencil suffer from Pogo Effect due to the long-thin design and the > > use of the SRB? > > Solid motors don't get pogo Pogo was a major unsolved problem at the Vandenberg Launch Site when the Challenger disaster was used as an excuse to abandon the billions wasted there, filament-wound SRB motors and all. JTM > > Will the Pencil suffer from Pogo Effect due to the long-thin design and the > > use of the SRB? > > Solid motors don't get pogo Why not? Considering the configuration of Ares 1 (long, thing tube like Titan II), I'd think it's possible regardless of the fuel. Don't forget, that this will be the first time an SRB has been used in this configuration rather than being attached to the _side_ of a launch vehicle on any real scale. >>> Will the Pencil suffer from Pogo Effect due to the long-thin design and > the [quoted text clipped - 6 lines] > rather than being attached to the _side_ of a launch vehicle on any real > scale. I think you are confusing resonance with POGO. POGO as I understand it is oscillation caused by positive feedback through the fuel delivery system (tank -> turbopump -> expansion chamber) which causes the thrust level to modulate. It does involve resonance with the rocket body but is only an issue in a liquid fuel rocket. Aside from POGO, it is possible to have a resonance issue where the rocket body is "highly tuned" (i.e. has a high Q factor) due to the diameter/length ratio and the stiffness of the body (i.e. long thin bodies which are very stiff tend to resonate more easily). I would think that Ares 1 would be prone to resonance issues (due to its mechanical configuration) but not POGO. If the body is highly tuned the energy put into it via the thrust will cause it to ring. If the ringing is large enough it can cause deflection which will exceed the structural limits of the airframe. > >>> Will the Pencil suffer from Pogo Effect due to the long-thin design and > > the [quoted text clipped - 22 lines] > is large enough it can cause deflection which will exceed the structural > limits of the airframe. You're right; 'oscillation' is the term. "Alan Erskine" <alan.erskine@bigpond.com> wrote in news:WV2xj.19684$421.13268 @news-server.bigpond.net.au: >> > Will the Pencil suffer from Pogo Effect due to the long-thin design and > the [quoted text clipped - 7 lines] > rather than being attached to the _side_ of a launch vehicle on any real > scale. Ummm, aren't Minuteman III solid? (just to pick a nit on the configuration aspect - I think Leopold gave the correct explanation of why solids won't pogo)  Signature--- there should be a "sig" here Is it the Indian vehicle which uses solids in this way or did I dream it? At any rate, the thrust from a solid is not terribly uniform, and cannot really be controlled once lit so any kind of cyclic burning and resonance in the system is goind to be a real problem to fix without making the whole thing heavier. Brian SignatureBrian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ______________________________________________________________________________________________________________ >> > Will the Pencil suffer from Pogo Effect due to the long-thin design and > the [quoted text clipped - 8 lines] > rather than being attached to the _side_ of a launch vehicle on any real > scale. There was the Scout, but that was small. The Indian LV uses solids for boost, not a main stage. Why not use the Delta IV Heavy - reliable, already available (little or no development cost) and the Orion seems sized for it (23 tonne mass, 5m diameter - same as the diameter of the D-IV fairing). > Is it the Indian vehicle which uses solids in this way or did I dream it? > [quoted text clipped - 4 lines] > > Brian ____________________________________________________________________________ __________________________________ > >> > Will the Pencil suffer from Pogo Effect due to the long-thin design and > > the [quoted text clipped - 8 lines] > > rather than being attached to the _side_ of a launch vehicle on any real > > scale. > Why not use the Delta IV Heavy - reliable, already available (little or no > development cost) and the Orion seems sized for it (23 tonne mass, 5m > diameter - same as the diameter of the D-IV fairing). why that would deny nasa the pork of building a entire new launch system to pay off shuttl;e contractors. besides it would of saved time and money.......... heck the money spent on boosters could of been used for a better service module and capsule........... why would nasa wanted to do any of that? its sensible and efficent. sadly thats not a nasa goal these days:( but while they screw around private industry will make them look really bad............ >Why not use the Delta IV Heavy - reliable, already available (little or no >development cost) and the Orion seems sized for it (23 tonne mass, 5m >diameter - same as the diameter of the D-IV fairing). Because Congress mandated using the Shuttle infrastructure/workforce to the greatest extent possible. Brian > On Wed, 27 Feb 2008 12:57:44 GMT, "Alan Erskine" > [quoted text clipped - 7 lines] > > Brian where did congress do the technical specs? nasa kept upsizing its capsule so it was too heavy for a expendable, only to find the capsule is too heavy for its solid configuration, its too big too heavy, not affordable and no one wants it. i sincerly hop private industry quickly builds a expendable while nasa is still writing specs. this would put nasa out of man to LEO:) > There was the Scout, but that was small. The Indian LV uses solids > for boost, not a main stage. The Indian GSLV uses a large solid core and liquid strap-ons, and is apparently unique in that configuration. Its successor will go back to a more traditional configuration of liquid core and solid strap-ons. http://en.wikipedia.org/wiki/GSLV Resonance is a problem for all solid motors, but appears to be worse in the larger and longer ones; the frequency is lower and the amplitude may be greater as well. Shuttle may have mitigated the issue by mounting the SRBs on the ET, which transmits less of the vibration to the orbiter. --Damon > > There was the Scout, but that was small. The Indian LV uses solids > > for boost, not a main stage. [quoted text clipped - 11 lines] > the issue by mounting the SRBs on the ET, which transmits less of > the vibration to the orbiter. Hi Damon. Good to find a familiar poster. I'm wondering if the Earth departure Stage will be sufficient to absorb the resonances. > --Damon >> Resonance is a problem for all solid motors, but appears to be >> worse in the larger and longer ones; the frequency is lower and [quoted text clipped - 6 lines] >I'm wondering if the Earth departure Stage will be sufficient to absorb the >resonances. Wrong launch vehicle. Brian |
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