Ares I and Max Q

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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Since the first stage of Ares I is a single SRB, how will they throttle down for Max Q? <br />Posted by willpittenger</DIV></p><p>The current shuttle SRBs have a grain geometry that reduces thrust at a pre-set time to manage max Q.&nbsp; You do it by putting in features like fins and grooves.&nbsp; It is pretty standard for solid rockets.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The current shuttle SRBs have a grain geometry that reduces thrust at a pre-set time to manage max Q.&nbsp; You do it by putting in features like fins and grooves.&nbsp; It is pretty standard for solid rockets. <br />Posted by DrRocket</DIV></p><p>To expand on this a little for those not as informed about solid propellant rockets: In order to design a propellant&nbsp;grain configuration that "throttles down" the grain is designed so that the&nbsp;propellant grain's burning surface area is reduced at the desired time. This reduces the motor's thrust. The "throttle up" is accomplished by increasing the propellant grain's burning surface area. Star centrral grain cores and smooth bore truncated cones are used in the SRBs to accomplish the thrust profile.&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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nimbus

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When we hear "go with throttle up", after the "Max-Q" message during Shuttle launches, how do they manualy throttle the engines up? &nbsp;Is the grain with lower surface area manualy added to, and afterwards removed from the burn mixture? <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>When we hear "go with throttle up", after the "Max-Q" message during Shuttle launches, how do they manualy throttle the engines up? &nbsp;Is the grain with lower surface area manualy added to the burn mixture? <br />Posted by nimbus</DIV></p><p>The computers throttle up the SSMEs by increasing the LOX flow rate into the engines. The call "Go for throttle up" is not a msg for the crew to performa action. It is simply a "heads up" to them of this event.</p> <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The computers throttle up the SSMEs by increasing the LOX flow rate into the engines. The call "Go for throttle up" is not a msg for the crew to performa action. It is simply a "heads up" to them of this event. <br />Posted by shuttle_guy</DIV></p><p>&nbsp;</p><p>To expand on my post a bit: The crew needs to be ready to watch for a SSME "stuck throttle". That is to verify that the SSME's do throttle up as expected. Otherwise they must perform corrective procedures and/or initiate an abort.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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Zipi

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>When we hear "go with throttle up", after the "Max-Q" message during Shuttle launches, how do they manualy throttle the engines up? &nbsp;Is the grain with lower surface area manualy added to, and afterwards removed from the burn mixture? <br />Posted by nimbus</DIV><br /><br />SRB's are solid rockets and during their operation they cannot be throttled. SSME's which are the shuttles engines are liquid motors and they can be throttled. <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>SRB's are solid rockets and during their operation they cannot be throttled. SSME's which are the shuttles engines are liquid motors and they can be throttled. <br />Posted by Zipi</DIV></p><p>&nbsp;</p><p>That is not correct. As I said above the Shuttle SRBs are throttled to reduce their thrust during Max Q. This has been a fact since the beginning of the program over 35 years ago.</p> <div class="Discussion_UserSignature"> </div>
 
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Zipi

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;That is not correct. As I said above the Shuttle SRBs are throttled to reduce their thrust during Max Q. This has been a fact since the beginning of the program over 35 years ago. <br />Posted by shuttle_guy</DIV><br /><br />Yes, but I have tought that once ignited nothing cannot be done to the SRBs, meaning that the throttling has been done when those things have been manufactured and it cannot be changed when ignited. <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Yes, but I have tought that once ignited nothing cannot be done to the SRBs, meaning that the throttling has been done when those things have been manufactured and it cannot be changed when ignited. <br />Posted by Zipi</DIV></p><p>s stated above the shape of the propellant grain core is used &nbsp;modify the thrust profile. The thrust is reduced to get the vehicle past Max Q</p><p>http://en.wikipedia.org/wiki/Image:Srbthrust2.jpg</p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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Zipi

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>s stated above the shape of the propellant grain core is used &nbsp;modify the thrust profile. The thrust is reduced to get the vehicle past Max Qhttp://en.wikipedia.org/wiki/Image:Srbthrust2.jpg <br />Posted by shuttle_guy</DIV><br /><br />So basically it cannot be throttled during the flight as I said... The throttling has been built in when the SRB is manufactured. What I'm trying to say is that pilots or ground controllers or computers&nbsp;cannot modify the throttle during the flight. <div class="Discussion_UserSignature"> </div>
 
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samkent

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Simplified<BR/><BR/>The two SRBs are manufactured with the throttle up and down built in and cannot be changed during flight.<BR/><BR/>The Shuttles three main engines are throttled up and down electronically during the flight.
 
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MeteorWayne

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So basically it cannot be throttled during the flight as I said... The throttling has been built in when the SRB is manufactured. What I'm trying to say is that pilots or ground controllers or computers&nbsp;cannot modify the throttle during the flight. <br />Posted by Zipi</DIV><br /><br />"Throttle" Definition from Merriam-Webster:</p><p><span class="sense_label start">2 a</span><span class="sense_content"><strong>:</strong>&nbsp;to decrease the flow of (as steam or fuel to an engine) by a valve</span> </p><p><span class="sense_label">b</span><span class="sense_content"><strong>:</strong>&nbsp;to regulate and especially to reduce the speed of (as an engine) by such means</span> </p><p><span class="sense_label">c</span><span class="sense_content"><strong>:</strong>&nbsp;to vary the thrust of (a rocket engine) during flight</span><span class="verb_class"><em>intransitive verb</em></span><span class="sense_content"><strong>:</strong>&nbsp;to throttle something (as an engine) &mdash;usually used with <em>back</em> or <em>down</em><span class="vi"><the pilot <em>throttled</em> back></span></span></p><div class="run_on">&mdash; </div><div class="run_on">So if you use def c, the SRB design applies. The more common definition is a and b which would apply to the Main Engines.</div><div class="run_on">In a way it's similar to the ice going away thing on Mars. While "evaporate" technically applies, "sublimate" specifically refers to solid to gas phase transition, so fits better.</div> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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Zipi

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Simplified The two SRBs are manufactured with the throttle up and down built in and cannot be changed during flight. The Shuttles three main engines are throttled up and down electronically during the flight. <br />Posted by samkent</DIV><br /><br />Exactly what I ment! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /></p><p>Nice to see that somebody can say it simple. I think that I have some language barrier preventing me to express myself the way I want, but I'll keep trying and hopefully learn more as the time goes on.</p> <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So basically it cannot be throttled during the flight as I said... </p><p>&nbsp;No that is not correct. The SRBs are throttled down in flight.</p><p>&nbsp;</p><p>The throttling has been built in when the SRB is manufactured. What I'm trying to say is that pilots or ground controllers or computers&nbsp;cannot modify the throttle during the flight. <br />Posted by Zipi</DIV></p><p>True</p> <div class="Discussion_UserSignature"> </div>
 
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willpittenger

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The current shuttle SRBs have a grain geometry that reduces thrust at a pre-set time to manage max Q.&nbsp; You do it by putting in features like fins and grooves.&nbsp; It is pretty standard for solid rockets.</p><p>Posted by DrRocket</DIV><br />Ok. I asked because I thought the shuttle did it all with the SSMEs.&nbsp; Since the Ares I won't have SSMEs in the first stage, I was left scratching my head. </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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<p>
Ok. I asked because I thought the shuttle did it all with the SSMEs.&nbsp; Since the Ares I won't have SSMEs in the first stage, I was left scratching my head. <br />Posted by willpittenger[/QUOT</p><p>There are also trajectory shaping maneuvers that can can be done with solids to get the desired end state for the trajectory.&nbsp; They don't help much with max Q but they do help get one into the proper orbit.&nbsp; U.S. ICBMs use solid motors for all by the 4th maneuvering stage.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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nimbus

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> To expand on my post a bit: The crew needs to be ready to watch for a SSME "stuck throttle". That is to verify that the SSME's do throttle up as expected. Otherwise they must perform corrective procedures and/or initiate an abort. <br /> Posted by shuttle_guy</DIV><br />Thanks a bunch shuttle_guy :) &nbsp;I thought the fuel grain shape was (verticaly) distributed inside the fuel tank to match the required thrust illustrated in this image: &nbsp; &nbsp; http://en.wikipedia.org/wiki/Image:Srbthrust2.jpg</p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thanks a bunch shuttle_guy :) &nbsp;I thought the fuel grain shape was (verticaly) distributed inside the fuel tank to match the required thrust illustrated in this image: &nbsp; &nbsp; http://en.wikipedia.org/wiki/Image:Srbthrust2.jpg <br />Posted by nimbus</DIV></p><p>The way solids are manufactured is this.&nbsp; Propellant is mixed in large mixers.&nbsp; Part of the formulation is a curative.&nbsp; The fluid propellant (thick but pourable) is poured into the case, in which there is a mandrel that provides the desired grain features, such as fins.&nbsp; Then the motor is cured, and the mandrel extracted.&nbsp; Depending on the specific designs, mandrel extraction may involve some disassembly.&nbsp; Sometimes there is secondary machining of the propellant grain to add other features.&nbsp;&nbsp;But in any case the grain features are designed to control the surface area as the propellant burns radially outward from the centerbore.&nbsp;</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;To expand on my post a bit: The crew needs to be ready to watch for a SSME "stuck throttle". That is to verify that the SSME's do throttle up as expected. Otherwise they must perform corrective procedures and/or initiate an abort.</p><p>Posted by shuttle_guy</DIV><br />And probably get ready for a kick in the back.</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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nimbus

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<p>I see, thank you :)&nbsp;</p><p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The way solids are manufactured is this.&nbsp; Propellant is mixed in large mixers.&nbsp; Part of the formulation is a curative.&nbsp; The fluid propellant (thick but pourable) is poured into the case, in which there is a mandrel that provides the desired grain features, such as fins.&nbsp; Then the motor is cured, and the mandrel extracted.&nbsp; Depending on the specific designs, mandrel extraction may involve some disassembly.&nbsp; Sometimes there is secondary machining of the propellant grain to add other features.&nbsp;&nbsp;But in any case the grain features are designed to control the surface area as the propellant burns radially outward from the centerbore.&nbsp; <br /> Posted by DrRocket</DIV></p> <div class="Discussion_UserSignature"> </div>
 
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