Getting more SRB thrust from Ares

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willpittenger

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I see the Ares V SRBs might get even larger.&nbsp; However, couldn't the Ares managers pull a page from the Atlas V and allow the number of SRBs attached to vary depending on needs?&nbsp; I figure an extra SRB would provide more thrust than extra segements. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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docm

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Why not just go to 6 segments?&nbsp; A longer burn but not as much stress on the overall structure vs. 3-4 SRB's going off at once. <div class="Discussion_UserSignature"> </div>
 
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Zipi

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I see the Ares V SRBs might get even larger.&nbsp; However, couldn't the Ares managers pull a page from the Atlas V and allow the number of SRBs attached to vary depending on needs?&nbsp; I figure an extra SRB would provide more thrust than extra segements. <br />Posted by willpittenger</DIV><br /><br />Shuttle_guy already answered to this at the other topic. The reason is too much G's at initial ascent and there are no ways to throttle down enough for max Q. So two SRBs seems to be the maximum.</p><p>I personally favor liquid motors instead of SRBs, like Energia&nbsp;booster had four of them and they vere throtteable like all liquid motors.</p> <div class="Discussion_UserSignature"> </div>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Shuttle_guy already answered to this at the other topic. The reason is too much G's at initial ascent and there are no ways to throttle down enough for max Q. So two SRBs seems to be the maximum.I personally favor liquid motors instead of SRBs, like Energia&nbsp;booster had four of them and they vere throtteable like all liquid motors.</p><p>Posted by Zipi</DIV><br />Actually, when Atlas V uses the maximum number of boosters, I don't know that it has to light all at once.&nbsp;&nbsp; Ares V could use the same strategy.&nbsp; Carry 3-4. But never light more than 2 at any one time.</p> <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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Cygnus_2112

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Why not just go to 6 segments?&nbsp; A longer burn but not as much stress on the overall structure vs. 3-4 SRB's going off at once. <br /> Posted by docm</DIV></p><p>&nbsp;</p><p>Increasing length, increases thrust (and would reduce the duration slightly).&nbsp; Longer duration burn requires a wider booster </p>
 
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Cygnus_2112

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I see the Ares V SRBs might get even larger.&nbsp; However, couldn't the Ares managers pull a page from the Atlas V and allow the number of SRBs attached to vary depending on needs?&nbsp; I figure an extra SRB would provide more thrust than extra segements. <br /> Posted by willpittenger</DIV></p><p>&nbsp;</p><p>&nbsp;The SRMs on Atlas are augmentation and not the primary booster.&nbsp; Also they don't support the vehicle on the pad.</p><p>&nbsp;</p><p>The pad&nbsp; mods for multiple SRB's would be horrendous, not to mention the problems with designing the ET to handle them</p>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Why not just go to 6 segments?&nbsp; A longer burn but not as much stress on the overall structure vs. 3-4 SRB's going off at once. <br />Posted by docm</DIV></p><p>A 6 segment SRB would probably not burn longer than a 4 or 5 segment SRB.&nbsp; In fact the burn time would probably be shorter.</p><p>The SRBs basically burn from a central port radially outward.&nbsp; And the higher the pressure the higher the burn rate.&nbsp; So if you increase the number of segments the amount of gas generated increases, increasing the pressure and increasing the burn rate.&nbsp; The burn distance doesn't change much, even with reasonable design changes, so the net result is a shorter action time.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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Cygnus_2112

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Actually, when Atlas V uses the maximum number of boosters, I don't know that it has to light all at once.&nbsp;&nbsp; Ares V could use the same strategy.&nbsp; Carry 3-4. But never light more than 2 at any one time. <br /> Posted by willpittenger</DIV></p><p>&nbsp;</p><p>They all ignite at T-0.&nbsp; Ares couldn't use the strategy you mention, the ET/SRB attachment are not designed to "carry" a fully loaded SRB.&nbsp; Also an SRB is too heavy to carry, it is a couple of millions of pounds.</p><p>&nbsp;&nbsp;</p>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;They all ignite at T-0.&nbsp; Ares couldn't use the strategy you mention, the ET/SRB attachment are not designed to "carry" a fully loaded SRB.&nbsp; Also an SRB is too heavy to carry, it is a couple of millions of pounds.&nbsp;&nbsp; <br />Posted by Cygnus_2112</DIV></p><p>If the&nbsp; strategy were desirable one ought to be able to design attachments to allow both air-start and ground-start SRBs.&nbsp; Delta II, for instance,&nbsp;does it on a smaller scale with much shorter burn times.&nbsp; I don't&nbsp; see why one would find that a good strategy for Ares however.&nbsp; It&nbsp;would limit g levels, but the gravity loss would be large.</p> <div class="Discussion_UserSignature"> </div>
 
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samkent

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quote "Longer duration burn requires a wider booster"<BR/><BR/>Not necessarily, the hollow center does not have to go all of the way to the top. It could stop at segment 3 or 4, leaving the final segment to burn from the bottom up. As opposed to the current center to the outside. But this will reduce the overall thrust in the final seconds. <BR/>Also changes in the propellant mix could also reduce the thrust at maximum aerodynamic pressure allowing a defacto “throttle down”.
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>quote "Longer duration burn requires a wider booster" Not necessarily, the hollow center does not have to go all of the way to the top. It could stop at segment 3 or 4, leaving the final segment to burn from the bottom up. As opposed to the current center to the outside. But this will reduce the overall thrust in the final seconds. Also changes in the propellant mix could also reduce the thrust at maximum aerodynamic pressure allowing a defacto &ldquo;throttle down&rdquo;. <br />Posted by samkent</DIV></p><p>If you did that it might be a bit hard to light.&nbsp; The igniter fires into that center bore.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>quote "Longer duration burn requires a wider booster" Not necessarily, the hollow center does not have to go all of the way to the top. It could stop at segment 3 or 4, leaving the final segment to burn from the bottom up. As opposed to the current center to the outside. But this will reduce the overall thrust in the final seconds. Also changes in the propellant mix could also reduce the thrust at maximum aerodynamic pressure allowing a defacto &ldquo;throttle down&rdquo;. <br />Posted by samkent</DIV></p><p>You do not reduce thrust for max q by altering the propellant mix.&nbsp; That would not be a reliable method.&nbsp; What you do is configure the propellan grain geometry to reduce burn surface area at the point at which you want to "throttle down".</p><p>Even if you could get the motor burning with a head-end grain (and there are ways to do that for smaller motors, but for an SRM size motor it would be a big problem) there are problems with end-burning grains that would need to be considered.&nbsp; One is a much thicker internal insulator to allow for the increased exposure time.&nbsp; Another is cone-buring that is typical of end-burners.&nbsp; And how long do you want to burn ?&nbsp; The propellant burn rate is in the range of 028 - 0.5 inches per second.&nbsp; But the surface area of an end burner is low so the thrust will be low as well.&nbsp; Probably too low to be of interest.</p><p>The bottom line is that longer duration requires a thicker propellant web and the practical way to get that is to increase the diameter.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;They all ignite at T-0.&nbsp; Ares couldn't use the strategy you mention, the ET/SRB attachment are not designed to "carry" a fully loaded SRB.&nbsp; Also an SRB is too heavy to carry, it is a couple of millions of pounds.</p><p>Posted by Cygnus_2112</DIV><br />I don't suppose the SRB design could be modified to use the hybrid technology that Rutan developed. </p> <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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DrRocket

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't suppose the SRB design could be modified to use the hybrid technology that Rutan developed. <br />Posted by willpittenger</DIV><br />&nbsp;Rutan did not invent hybrid technology.&nbsp; It has been investigated for quite a while, and it has some serious drawbacks.&nbsp; In any case the shuttle SRBs could not be modified in any practical way to be hybrids.&nbsp; Even if you could, that is not likely to increase thrust.&nbsp; One real problem with hybrids is the low recession rate of the propellant grain.&nbsp; To get decent gas generation, hence thrust you need to have a lot of surface area, and that hurts badly in mass fraction. <div class="Discussion_UserSignature"> </div>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Rutan did not invent hybrid technology.&nbsp; It has been investigated for quite a while, and it has some serious drawbacks.&nbsp; In any case the shuttle SRBs could not be modified in any practical way to be hybrids.&nbsp; Even if you could, that is not likely to increase thrust.&nbsp; One real problem with hybrids is the low recession rate of the propellant grain.&nbsp; To get decent gas generation, hence thrust you need to have a lot of surface area, and that hurts badly in mass fraction.</p><p>Posted by DrRocket</DIV><br />There was a book I read a decade ago in which the Soviets (the USSR had not broken up and Gorbachev had been assasinated) used a different sort of hybrid with a pelletized fuel.&nbsp; There isn't a way to modify the SRBs like that, but I wonder if that would be better. </p> <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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Cygnus_2112

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>There was a book I read a decade ago in which the Soviets (the USSR had not broken up and Gorbachev had been assasinated) used a different sort of hybrid with a pelletized fuel.&nbsp; There isn't a way to modify the SRBs like that, but I wonder if that would be better. <br /> Posted by willpittenger</DIV></p><p>&nbsp;The SRB's have to be used as is, no modifications to the basic fit and form.&nbsp; That is the reason that are being used.&nbsp; A clean sheet design would not use the SRBs and instead use liquid boosters. </p><p>&nbsp;</p><p>Also a hybrid booster would need a large oxidizer tank. &nbsp;&nbsp;</p>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;The SRB's have to be used as is, no modifications to the basic fit and form.&nbsp; That is the reason that are being used.&nbsp; A clean sheet design would not use the SRBs and instead use liquid boosters. &nbsp;Also a hybrid booster would need a large oxidizer tank.</p><p>Posted by Cygnus_2112</DIV><br />Uh, the engine I mentioned in that book didn't need an oxidizer.&nbsp; The fuel was the same type of fuel used in normal solid fuel rockets, but in pellet form.&nbsp; The pellets enter the chamber via the same type of mechanism used by pellet stoves.</p> <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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Zipi

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Uh, the engine I mentioned in that book didn't need an oxidizer.&nbsp; The fuel was the same type of fuel used in normal solid fuel rockets, but in pellet form.&nbsp; The pellets enter the chamber via the same type of mechanism used by pellet stoves. <br />Posted by willpittenger</DIV><br /><br />Sounds pretty solid to me... <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" /> <div class="Discussion_UserSignature"> </div>
 
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Cygnus_2112

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Uh, the engine I mentioned in that book didn't need an oxidizer.&nbsp; The fuel was the same type of fuel used in normal solid fuel rockets, but in pellet form.&nbsp; The pellets enter the chamber via the same type of mechanism used by pellet stoves. <br /> Posted by willpittenger</DIV></p><p>So what advantage would that have?&nbsp; Not more thrust.&nbsp;</p>
 
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trailrider

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;The SRB's have to be used as is, no modifications to the basic fit and form.&nbsp; That is the reason that are being used.&nbsp; A clean sheet design would not use the SRBs and instead use liquid boosters. &nbsp;Also a hybrid booster would need a large oxidizer tank. &nbsp;&nbsp; <br />Posted by Cygnus_2112</DIV></p><p>The Shuttle SRB's (4-segment) are NOT being "used 'as-is'!"&nbsp; Changing from 4-segments to five, adding a roll-control of some kind, and going to a larger diameter core on Ares V is like jacking up the radiator cap on an old car and "just" changing to a more powerful engine, different fuel, swapping the transmission, etc....and then changing the radiator cap.&nbsp; A far better solution to all of this, that would permit the use of the same ground infrastructure, manufacturing tooling, and LEO rendezvous, plus allowing larger payloads to LEO, would be the Jupiter launch vehicles proposed in DIRECT.</p><p>Ad Luna! Ad Ares! Ad Astra!</p>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Uh, the engine I mentioned in that book didn't need an oxidizer.&nbsp; The fuel was the same type of fuel used in normal solid fuel rockets, but in pellet form.&nbsp; The pellets enter the chamber via the same type of mechanism used by pellet stoves. <br />Posted by willpittenger</DIV></p><p>A concept of that basic sort has been considered,&nbsp;for a&nbsp;very small rocket motor of the station keeping type.&nbsp; It has all sorts of problems and virtually no advantages.</p><p>You could not use the pellet stove mechanism for two reasons.&nbsp; First, rocket motors operate at high pressure, and you want all of the gas to go out the nozzle and not back through an open feed channel.&nbsp; Second, those hot gasses going back through the feed channel would set off all of the pellets in your hopper at once, and that would get really exciting -- loud noises and pieces flying around at high velocity.&nbsp; You need a tight gas seal between the pellet magazine and the combustion chamber.&nbsp; That sort of mechanism can get to be very complicated and that complication eliminates the advantages of a solid fuel rocket.</p><p>A complicating issue is that solid fuels are basically explosives, some more so than others, and&nbsp;small pieces having a combined high surface area can react very violently to certain stimuli --&nbsp; friction, impact, electrical discharge.&nbsp; So you need to be very careful in handling pellets, and among things make sure that you create no dust or anything that might behave like dust.&nbsp; If&nbsp;you started binding or grinding anything in the auger of your pellet feeder it could get real bad.&nbsp; Continuous mixers using a screw mechanism have been used for making solid propellant, and there have been some fairly&nbsp;spectatular fires as well.&nbsp; It can be done but it takes some expertise to do it.</p> <div class="Discussion_UserSignature"> </div>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So what advantage would that have?&nbsp; Not more thrust.</p><p>Posted by Cygnus_2112</DIV><br />You could throttle it or even turn it off.</p> <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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Zipi

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You could throttle it or even turn it off. <br />Posted by willpittenger</DIV><br /><br />This is true, but I guess that throttling such thing is not very dynamic... Actually I'm pretty sure that the throttle response will be pretty poor (if even possible), but somebody who knows can of course say better. <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>This is true, but I guess that throttling such thing is not very dynamic... Actually I'm pretty sure that the throttle response will be pretty poor (if even possible), but somebody who knows can of course say better. <br />Posted by Zipi</DIV></p><p>If you are basically feeding in pellets that burn in real time the throttle response ought to be pretty good, but not like a liquid.&nbsp; That is assuming that you overcome all of the other hurdles.</p><p>Unfortunately the other hurdles are quite high, increasing in height very quickly with motor thrust requirements.&nbsp; And if you overcome them all that you have is a motor that&nbsp;will do&nbsp;what can now be done rather easily with a liquid.&nbsp; No such system currently exists or is likely to.&nbsp; I don't think there is any ongoing work to consider such a thing,&nbsp; and I am pretty sure on that score.&nbsp; It is a classic case of&nbsp;high risk and low payoff.</p><p>The basic difficulty is that this concept, even more so than hybrids, manages to combine the worst aspects of solids and liquids.&nbsp; It is as complex if not more so than a liquid, with lower Isp, poor mass fraction cmpared to a solid, less throttle control than a liquid, a pre-mixed fuel-oxidizer propellant of high surface area with associated hazards, more difficult fuel management, ...</p> <div class="Discussion_UserSignature"> </div>
 
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samkent

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If the top segment doesn't have a hollow center it would have to burn from the end. The result would be a longer burn at a reduced thrust. Wouldn't this also reduce the higher g forces close to burn out?
 
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