Solid vs Liquid Rocket boosters on Shuttle

[spd405]

What was the reasoning behind using solid rocket boosters and not liquid rocket boosters on the shuttle system?

 

[nacnud]

Solids were easier and cheaper.

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Solids were easier and cheaper. <p><hr /></p></p></blockquote><br /><br />Certainly not the Shuttle SRB. The choice for keeping the RSRM is a NASA job decision, not technical nor economical. <div class="Discussion_UserSignature"> </div>

 

[steve82]

Back then "reusable" was automatically equated with "economic" although the two are not necessarily synonymous when overall costs of recertification and refurbishment between missions are considered. Some people said reusable SRB's are just lip service to the reusable concept.

 

[drwayne]

Note that you can do things with solids that you cannot easily do with liquids. Despite a lower ISP, their nature as pre-mixed fuel/oxidizer means that you can get a lot of total thrust out of them with simple geometry. To do the same things with liquids requires high performance pumps to get fuel and oxidizer together. Heaven knows they had enough trouble with the blades of the shuttles main engine turbo-pumps.<br /><br />You of course buy with solids into the "once they are lit, you are along for the ride" issue.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[trailrider]

From a pure performance standpoint, if you multiply the overall density (including the rocket motor casing, nozzle hydraulics packages, etc.) times the Isp (specific impulse, or lbs of thrust per lb of propellant used per second), you get the Density-Specific Impulse. Solids in the class of the Shuttle SRBS have a relatively higher Density-Specific Impulse than similar-performing liquids would have in the configuration of the Shuttle stack.<br /><br />The original shuttle concept called for a re-usable, manned fly-back booster, with jet as well as rocket engines. I don't recall if they intended to launch horizontally or not, but it is possible.<br /><br />When it became obvious that you could not build the whole thing for an amount of money that could be obtained from Congress. The technology developments required for the TPS (tile system), and the SSME's ate up too much money. The Shuttle Solid Rocket Boosters could be recovered by parachute. The amount of money saved on the first three or four flights (NOT including the one where the ringing frequency of the separation ring firing triggered the Main Deck Fitting separation explosive bolt firings and we lost both boosters...STS-4) paid for the development of the parachute subsystem (SRB Decelerator SubSystem), about $24M. <br /><br />Solid rocket boosters have been used very successfully (though NOT without spectacular failures) on the Titan III and IV. <br /><br />The rationale behind using a single SRB for launching a CEV is that the boosters are already "man-rated"! This saves a long and expensive series of static and flight tests that would be required for any other vehicle, including the Atlas V and Delta-IV.<br /><br />If this sounds great, I've got a launch pad on Merritt Island I'll sell you for 5M laudinium credits!<br /><br />Yeah, I've worked liquids and I'ves worked solids, and for manned and/or high-value payloads, I wouldn't want anything to do with a large firecracker, an escape tower built into the forwar

 

[drwayne]

I thought about mentioning fuel density, and decided for some reason not to. But you did such a good job, I am *glad* I did not.<br /><br /><img src="/images/icons/smile.gif" /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>If this sounds great, I've got a launch pad on Merritt Island I'll sell you for 5M laudinium credits! <p><hr /></p></p></blockquote><br /><br />LOL... Would you take a cyber-check? ... LOL <div class="Discussion_UserSignature"> </div>

 

[dwightlooi]

There is a misconception that SRBs are less safe than liquid boosters. This is not really true. In fact, for the most parts solids are safer! Let me explain.<br /><br />(1) Most liquid boosters have a two highly energetic liquids in their tanks. Sometimes these are hypergolic fluids (eg. N2O4 and UDMH) which will blow sky high when combined. But even when the fluids are not hypergolic (eg. kerosene + LOX or LH2 + LOX) the usual result of a catastropic tank rupture is the same. In an ascending rocket there will almost always be that spark or flame around to blow the mix sky high. Solids on the other hand generally are not capable of blowing up. They burn but they never explode. A case rupture may cause a loss of forward motivation and probably a side side which will cause the ricket to lose control, but it won't blow up. It won't blow up because the solid fuel mixture is not capable of exploding. Chances are there will be plenty of time to fire a launch escape tractor or pusher setup and get your capsule to safety.<br /><br />(2) Liquids have a lot of things that can fail. turbo pumps, cooling loops around the nozzle, pressure lines back to the tank, combustion chambers. As lot of these things can cause an explosion. A solid is basically a tube with propellants in it. There are usually no moving parts save for the gimballing mechanism for the nozzle. There are less things to fail and things that are there and can fail cannot cause a big explosion. At worst, you will have an out of control rocket.<br /><br />(3) Solids also do not need to be fueled prior to launch or de-fueled if the launch is cancelled. They do not need fuel tanks and fueling aparatus near the launch tower. They do not need foam insulation. They can be stored for a long time and they need practically no prep time prior to launch.<br /><br />(4) Solids are superior in terms of propellant density. Even though specific impulse is lower and the payload fraction of a solid is smaller by mass, a solid is smaller t

 

[propforce]

There is a misconception that SRBs are safer than liquid boosters <img src="/images/icons/tongue.gif" /><br /><br />Three words: Electric Static Discharge<br /><br />Just ask the Brazilian Aerospace folks.<br /><br />It is true that LH2/LO2 system requires a better know-how to design and operate, and it is more complex. LO2/Kerosene system is safer in comparison. But both system can be checked-out and stored much safer than the solids. <br /><br />Liquid (non-hypergolics) do not "explode", they just leak. In the presence of ignition, they deflagate but not detonate. <br /><br />BTW, We don't use hypergolics for booster like the communists do ! <div class="Discussion_UserSignature"> </div>

 

[scottb50]

No, it was determined by the horses ass who was in the Senate when it was decided the SRB's had to be serviced in Utah. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">"Liquid (non-hypergolics) do not "explode", they just leak."</font><br /><br />Isn't it even harder to get hypergolics to explode? Non-hypergolics can be mixed to an exploding ratio and then detonated. Sometimes this has happened in rocket engines, ignition happens too late when reaction chamber is already filled with propellants, BOOM, a hard start. But you cannot premix hypergolics because ... well.. them being hypergolic <img src="/images/icons/wink.gif" /><br /><br />But most of them are quite toxic and expensive, bad for the environment and bad for the maintenance costs. How much does rocket grade H2O2 cost these days? That might be a good poor man's hypergolic, use as an oxidizer but divert part of the flow through catalyzing bed before entering the chamber.

 

[drwayne]

You can look the horses thing up at Snopes, it is an urban legend....<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[spd405]

Were any studies done on replacing the SRB's with LRB's following the Challenger explosion?

 

[najab]

<blockquote><font class="small">In reply to:</font><hr /><p>There is a misconception that SRBs are safer than liquid boosters<br /><br />Three words: Electric Static Discharge<br /><br />Just ask the Brazilian Aerospace folks.<p><hr /></p></p></blockquote>It takes more than ESD to ignite most solid rocket fuels. For example, it takes a small rocket motor to light the Shuttle's SRBs - I could be wrong, but you probably could take a match to a lump of the propellant and it wouldn't burn.<p>To the best of my knowledge, the Brazilian rocket ignited because the ignition circuits were inadvertently energised.</p>

 

[giofx]

Energia used liquid, but were they hypergolic or LO2/Kerosene?

 

[najab]

It lives on as the Zenit booster stage - it's a LOX/Kerosene motor.

 

[giofx]

oh, i see... thanks najab!

 

[tap_sa]

<font color="yellow">"It is very bad if the fuel valve opens before the oxid valved and there is a slug of fuel in the chamber when the Oxid gets there....boom"</font><br /><br />But isn't this the ordinary way to start about any rocket engine? Fuel flow starts first because the reaction chamber and nozzle doesn't like pure oxidizer. With non-hypergolic engines you have to make sure the the igniter is working then first drops of oxidizer enter the chamber, so that burning starts instantly. With hypergolics this is guaranteed, pressure builds up gradually and pushes the excess fuel away without any greater damage.<br /><br />The really bad thing is when non-hypergolic propellants, both fuel and oxidizer, fill the rocket chamber too much before ignition happens. Then you have way too much mass of possible detonable mixture of propellant in the chamber, more than there's ever supposed to be. When that finally ignites, then it is time to duck and cover.

 

[tap_sa]

<font color="yellow">"the excess fuel would detonate. "</font><br /><br />All by itself, without oxidizer?

 

[tap_sa]

<font color="yellow">" we need an expert to tell us."</font><br /><br />Indeed. It's these technical propulsion issues that interest me the most. Without efficient, reliable and cheap propulsion all other space dreams stay as space dreams.

 

[drwayne]

Is the question here which flow starts first?<br /><br />For many systems, the fuel starts first, as it is used (in one way or the other) to begin driving the turbo-pumps.<br /><br />Note that in normal operation, most systems run slightly fuel rich. This is one of those topics that has several explanations and is complicated. I am sure there is a Henry Spencer explanation somewhere...<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[najab]

The simple explaination is, of course, that if it can oxidize fuel it can also oxidize hot metal. As such, it would probably be a bad idea to have large amounts of it in the exhaust.

 

[drwayne]

"if it can oxidize fuel it can also oxidize hot metal"<br /><br />True. The drawback is that you have to be really careful about seals and stuff to insure that things do not start mixing in the turbopump.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

Is this along the lines of what you are asking?<br /><br />http://en.wikipedia.org/wiki/Rocket_fuel#Mixture_ratio<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>