Ridin' "The Stick": Dangerous, Complex, Cancelled?

SpaceKiwi · Oct 8, 2005

I was thinking exactly the same thing. A SRB is not a particularly complicated rocket motor as such things go, yes? It has always seemed like a heck of an effort to recover those things from Shuttle launches. The costings, reusuable vs expendible, must be marginal at best surely? <div class="Discussion_UserSignature"> Who is this superhero? Henry, the mild-mannered janitor ... could be!-------------------------------------------------------------------------------------------Bring Back The Black! </div>

Swampcat · Oct 9, 2005

"The vehicle C.G. will be too far aft and the larger diameter upper stage and SM/CM (assumed to be dummy for the first flight) move the C.P. forward. Thus it appears to me that fins will be required to be added to the SRB aft skirt." I'm currently working on a flying scale model of the CEV (affectionately referred to as The Corndog <img src="/images/icons/smile.gif" />) and am interested in whether or not the final design will have fins. The earlier drawings included fins while the last set of drawings did not. I've done some Rocksim simulations and it is possible that my model will work without fins. The problem is that I'd have to add a lot of weight in the nose. If that's what I have to do to make it fly then so be it, but I'd rather not since it seriously affects performance. Anyway, I was under the impression that the SRB has a thrust vector control system. I sort of understand the CP/CG relationship thing, but couldn't the thrust vector control system deal with marginal stability? What am I missing and what's the likelihood that fins will be included in the final design? <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

najab · Oct 10, 2005

One possible solution to the fins problem is to design them in such a manner that they break off on water impact. This shouldn't be too much of an engineering challenge, since the water impact forces are in the opposite direction to aerodynamic forces during launch.

tap_sa · Oct 10, 2005

If the roll control is done with verniers then why would Stick need fins at all?

tap_sa · Oct 10, 2005

Aren't practically all LVs nose-heavy aka unstable relying on active TVC to keep the right end pointing forward?

najab · Oct 10, 2005

Correct me if I'm wrong, but is problem that late in first-stage flight the (nearly) empty SRB case weighs so little in comparison to the fully loaded second stage?

Swampcat · Oct 10, 2005

"...is problem that late in first-stage flight the (nearly) empty SRB case weighs so little in comparison to the fully loaded second stage?" Good point, najaB. I hadn't thought of that. Makes sense. How much thrust does the TVC need from the SRB to maintain its ability to maintain the correct attitude? Or does it not use the SRB thrust? I was under the impression that the TVC gimbaled the nozzles. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

tap_sa · Oct 10, 2005

I messed up my earlier post by equating nose heavy to unstability. With shuttlecocks and all the actual case is of course the opposite. The more nose heavy the more Cg is ahead of Cp and the more stable the craft. I believe najaB's case later in the flight is when the Stick is most stable, Cg in the front within fully fueled second stage + payload while nearly empty SRB case acts as an giant feather wanting to keep the proper orientation. Biggest unstability should occur early in the flight. The SRB is thin and very dense compared to ordinary liquid stages so it brings Cg aft and thicker upper stage + payload pushes Cp front. It may be that a nominal flight would not require fins but certain abort situations do. IIRC this was the case with Saturn V, the little fins in the first stage were only for early aborts to keep the vehicle (with now engines shut or shutting down) steady enough for LES to work properly. I bet S_G knows the whole deal but would have to kill us if he told <img src="/images/icons/wink.gif" /> Perhaps N-1 style simple drag plates would suite the Stick. Jettison them after burn or have them hinged and retract before splash. swampcat: SRB's throat sits in a spherical socket in the case, allowing gimbaling it and the attached nozzle. The entire thrust is vectored.

Swampcat · Oct 10, 2005

"swampcat: SRB's throat sits in a spherical socket in the case, allowing gimbaling it and the attached nozzle. The entire thrust is vectored." Thank you. That was my understanding. Which led me to najaB's point about the empty SRB case. This implies a drop in thrust as propellant is expended. I was curious to know if there was a point where the TVC is not longer effective. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

Swampcat · Oct 10, 2005

"I believe najaB's case later in the flight is when the Stick is most stable, Cg in the front within fully fueled second stage + payload while nearly empty SRB case acts as an giant feather wanting to keep the proper orientation." Agreed. The question becomes "what is proper orientation?" I suppose you're referring to a nose forward attitude <img src="/images/icons/smile.gif" />. I was thinking about how the single SRB manages to guide itself along the proper launch path if the TVC becomes less effective. That's a little more than a basic stability issue. In the STS, the Orbiter's main engines provide this function. Hey, I'm just an amateur rocket scientist here. Trying to understand how this thing works. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

tap_sa · Oct 10, 2005

"I was thinking about how the single SRB manages to guide itself along the proper launch path if the TVC becomes less effective. That's a little more than a basic stability issue." That's good thinking! the TVC issue depends on how NASA is going to do the staging. Wait patiently till the SRB burns out or do thrust termination while there's still plenty of it. Latter is done by blowing up some explosives which open vent ports to the front end of the motor case. This effectively shuts down the motor instantly. If they wait till burn out the last seconds may have very unstable thrust. At least it looks that way if you look the latest shuttle ascent video, when SRBs start to dim out their plume has irregular puffs before jettisoning. Needless to say this is where liquid engines excell with their controlled, quick shutdown. "I'm just an amateur rocket scientist here. Trying to understand how this thing works." Ditto <img src="/images/icons/wink.gif" />

drwayne · Oct 10, 2005

"Yes, the SRB TVC gimbals the nozzle which is a engineering feat for a solid rocket motor." I don't remember if the shuttle SRB's do this, but I have worked on some program in which the TVC maintained a constant, low amplitude dither to keep the joint from slagging up and freezing. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

tap_sa · Oct 10, 2005

"The SRB staging on a single stick will be the same as on the Shuttle; when the chamber pressure drops below 50 psi. " OK. But will there be some form of sep motors to pull the SRB away? 50psi times SRB throat area is still a lot of force pushing towards interstage.

drwayne · Oct 10, 2005

I think y'all have better joints than we did. Oops, I am not sure that sounded right! <img src="/images/icons/wink.gif" /> Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

tap_sa · Oct 10, 2005

Did your TVC program fly on some actual vehicle?

drwayne · Oct 10, 2005

Yes sir, that it did. I worked on a program called THAAD for 7 years. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

tap_sa · Oct 10, 2005

Hit-to-kill missile defence missile, that's way too cool! I imagine missile hitting another is difficult enough even without extra wigling of TVC, must have been some über-precision program <img src="/images/icons/laugh.gif" />

drwayne · Oct 10, 2005

Our booster was only with us for a short time at the beginning of flight - then we were largely ballistic. Booster was, in the words of many - hotter than a '57 Chevy. The entertaining thing was that, due to the constraints of testing at White Sands, we had to do some energy wasting. So, early in the flight, we basically did a spin in which the thrust vector was at about 90 degrees to the velocity vector. You can find movies of it on the net. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

Swampcat · Oct 10, 2005

"The thrust essentially remains steady except for those 2 area of the profile." <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

Swampcat · Oct 10, 2005

"The SSME TVC is not steering the vehicle until after SRB sep." Thanks, S_G. I should have said "could provide this function if necessary" since I wasn't sure. I'd still have been wrong. It happens. <img src="/images/icons/blush.gif" /> <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

bwhite · Oct 10, 2005

As I recall, the 4 segment RSRM has 192,000 pounds of dry mass other than fuel and was designed using 1970s metallurgy. Might ATK move to composites or other 21st century material for at least part of the stick and go disposable? Every pound removed from dry mass can be added to 2nd stage payload, correct? Cut that 192,000 down to 128,000 and that adds 64,000 pounds to the 2nd stage perhaps doubling net payload to LEO.

drwayne · Oct 10, 2005

Didn't they go to new filament wound cases some years ago? Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

najab · Oct 10, 2005

No. The filament-wound casings died along with SLC-6, which is just as well since many people expected them to rupture on ignition.

drwayne · Oct 10, 2005

Yeah, darn I am getting forgetful, that died around the time of Challenger... Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

vogon13 · Oct 10, 2005

The space shuttle orbiter has three auxillary power units, each SRB has two. The units are actually quite similar, power output (IIRC) is around 150 horsepower. The units are powered with hydrazine which is decomposed upon a catalyst, and the resulting conflagration spins a smallish turbine at ~70,000 RPM. This is geared down to operate a hydraulic pump which provides flow to what are essentially hydraulic cylinders that on the orbiter move the aerodynamic surfaces and the gimballing of the 3 main engines while they are firing. The SRB units power hydraulic cylinders that control the orientation of the rocket nozzle. Each SRB carries 2, but only one is required for safe operation of the steering system. Orbiter must have 2 operable APUs although all three are operated concurrently. APU units are refurbished at the Hamilton Sundstrand facility in Rockford Ill. Test cells are massive concrete chambers lined with wooden planks. This is to contain fragments if a turbine wheel ruptures (the 70,000 RPM thing). To my knowlege, this has only occured once or twice since program inception in the seventies. The orbiter APU test facility incorporates actual switches and circuitry the same as on the orbiter for authenticity in testing. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Ridin' "The Stick": Dangerous, Complex, Cancelled?

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