strap-on motors

[spacy600]

<p>What are the trade offs between solid rocket and hybrid rocket strap-on motors?</p><p>price</p><p>performance</p><p>safety</p><p>toxicity</p>

 

[Cygnus_2112]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>What are the trade offs between solid rocket and hybrid rocket strap-on motors?priceperformancesafetytoxicity <br /> Posted by spacy600</DIV></p><p>complexity, reliability, size, history</p>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>complexity, reliability, size, history <br /> Posted by Cygnus_2112</DIV></p><p>&nbsp;</p><p>Ok so hybrids are a waste of time and effort.</p><p>Thanks for your response.&nbsp;</p>

 

[scottb50]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Ok so hybrids are a waste of time and effort.Thanks for your response.&nbsp; <br /> Posted by spacy600</DIV></p><p>&nbsp;</p><p>Not so much a waste of time as a waste of resources. Strapons are basically to get off the ground with and then they are discarded, the simpler they are the better. a hybrid solid would be more suitable as a re-usable stage because it is more complex having an oxidizer containment and feed system rather then an all inclusive propellant load. </p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Not so much a waste of time as a waste of resources. Strapons are basically to get off the ground with and then they are discarded, the simpler they are the better. a hybrid solid would be more suitable as a re-usable stage because it is more complex having an oxidizer containment and feed system rather then an all inclusive propellant load. <br />Posted by scottb50</DIV></p><p>Hybrids have a number of problems.&nbsp; Probably foremost is a low recession rate for the propellant.&nbsp; Because it burns slowly, in order to get adequate mass flow and therefore adequate thrust a lot of surface area is needed.&nbsp; In order to get enough surface area you are forced to use propellant geometries that result in a poor mass fraction.&nbsp; That eliminates one of the major advantages of solids.&nbsp; In addition hybrids have a tendancy towards large acoustic pressure oscillations.&nbsp; I have seen traces with oscillations on the order of 100 psi, and that is a lot.&nbsp; This might be alleviated with advances in detailed combustion chemistry, but so far I don't think those advances have been forthcoming.</p><p>Basically, in my opinion, hybrids manage to combine the worst of solids and liquids.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Hybrids have a number of problems.&nbsp; Probably foremost is a low recession rate for the propellant.&nbsp; Because it burns slowly, in order to get adequate mass flow and therefore adequate thrust a lot of surface area is needed.&nbsp; In order to get enough surface area you are forced to use propellant geometries that result in a poor mass fraction.&nbsp; That eliminates one of the major advantages of solids.&nbsp; In addition hybrids have a tendancy towards large acoustic pressure oscillations.&nbsp; I have seen traces with oscillations on the order of 100 psi, and that is a lot.&nbsp; This might be alleviated with advances in detailed combustion chemistry, but so far I don't think those advances have been forthcoming.Basically, in my opinion, hybrids manage to combine the worst of solids and liquids. <br /> Posted by DrRocket</DIV></p><p>Have you seen the work done at Stanford with wax?</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Have you seen the work done at Stanford with wax? <br />Posted by spacy600</DIV></p><p>Yes.&nbsp; That is the work in fundamental combustion physics to which I made reference.&nbsp; It has a long way to go before it becomes practical, but it is a step in the right direction.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Yes.&nbsp; That is the work in fundamental combustion physics to which I made reference.&nbsp; It has a long way to go before it becomes practical, but it is a step in the right direction. <br /> Posted by DrRocket</DIV></p><p>I agree it has a ways to go, but the wax hybrid might be refined enough to eliminate the problems you pointed out. The Spaceship 1 and 2 also point out the usefullness of hybrids. As far as being used as a strap on disposable booster I don't see hybrids being practical, the cost of building one would be a magnitude of order above a simple solid booster. As far as using them to provide the majority of thrust for initial flight, like the Shuttle SRB's re-usability would be a key factor.</p><p>The reality of the Shuttle SRB is the cost of recycling has never come close to just throwing them away. Recovery, cleaning, shipping to Utah and back as well as the cost of inspection negates any savings of reuse. With a TSTO design the SRB's could be integrated into the vehicle and simply refueled as the liquid tanks could be, making a hybrid motor a good choice. </p> <div class="Discussion_UserSignature"> </div>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> I don't see hybrids being practical, the cost of building one would be a magnitude of order above a simple solid booster.<br /> Posted by scottb50</DIV></p><p>According to this:</p><p>http://www.stanford.edu/~cantwell/AA283_Course_Material/AA283_Course_Notes/Chapter_11_Hybrid_Propulsion.pdf</p><p>Hybrids are cheaper and simpler then soilds. But yes it is in research&nbsp; and development.</p><p>&nbsp;</p><p>Dr Rocket, where do you see this tech going? What is it's potential? In what time frame?</p><p>I know it all comes down to funding...&nbsp;</p>

 

[spacy600]

<p>Reading all this stuff, I have a idea.</p><p>Hybrid motors have the fuel grains along the inside of the&nbsp; case, with ports, like "wagon wheel"</p><p>So what would happen if you hung the grain in the center, like a annular aerospike?&nbsp;</p><p>Then run the oxidzer along the outside of the grain?</p><p>How would theis affect the performance? Has anybody tried this? &nbsp;</p>

 

[Cygnus_2112]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Reading all this stuff, I have a idea.Hybrid motors have the fuel grains along the inside of the&nbsp; case, with ports, like "wagon wheel"So what would happen if you hung the grain in the center, like a annular aerospike?&nbsp;Then run the oxidzer along the outside of the grain?How would theis affect the performance? Has anybody tried this? &nbsp; <br /> Posted by spacy600</DIV></p><p>&nbsp;</p><p>What would insulate the casing, unburned propellant in the standard method serves this purpose.&nbsp; What supports the grain in the center, the propellant is bonded to the case in the standard method. </p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I agree it has a ways to go, but the wax hybrid might be refined enough to eliminate the problems you pointed out. The Spaceship 1 and 2 also point out the usefullness of hybrids. As far as being used as a strap on disposable booster I don't see hybrids being practical, the cost of building one would be a magnitude of order above a simple solid booster. As far as using them to provide the majority of thrust for initial flight, like the Shuttle SRB's re-usability would be a key factor.The reality of the Shuttle SRB is the cost of recycling has never come close to just throwing them away. Recovery, cleaning, shipping to Utah and back as well as the cost of inspection negates any savings of reuse. With a TSTO design the SRB's could be integrated into the vehicle and simply refueled as the liquid tanks could be, making a hybrid motor a good choice. <br />Posted by scottb50</DIV></p><p>You don't get to refuel hybrids like you do a liquid.&nbsp; They still have an ablative insulator,&nbsp; And if you use a composite case, like almost all rocket motors except the shuttle SRBs, you won't be able to wash them out re-insulate and cast new propellant.</p><p>Also, even if the work at Stanford cracks the combustion issues associated with pressure oscillations, you still have to contend with low mass fraction and the complexity of providing an oxidizer that is not integrated with the fuel.&nbsp; I have a hard time seeing how that is in any way superior to even a simple liquid system, say kerosene/LOX.</p><p>Also while I share your skepticism about the economics of the re-use of shuttle SRB cases, I know people with a good deal of data who disagree.&nbsp; But they do have a dog in the hunt.&nbsp; Quite a bit of the savings supposedly comes from refurbishment of the thrust vector actuator system, and that is probably real.&nbsp; That system is a fairly sophisticated gs generator powered hydraulic system and extremely expensive.&nbsp; The other thing is that those steel case segments do not grow on trees.&nbsp;&nbsp; I don't think any new ones have been made for quite a while (I might be wrong but I don't think so) and I don't know if the tooling is still in place to make new ones.&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>According to this:http://www.stanford.edu/~cantwell/AA283_Course_Material/AA283_Course_Notes/Chapter_11_Hybrid_Propulsion.pdfHybrids are cheaper and simpler then soilds. But yes it is in research&nbsp; and development.&nbsp;Dr Rocket, where do you see this tech going? What is it's potential? In what time frame?I know it all comes down to funding...&nbsp; <br />Posted by spacy600</DIV></p><p>Personally I don't see hybrids going anywhere.&nbsp; They have been the subject of a low level of R&D for many years.&nbsp; The benefits simply don't compensate for the problems.&nbsp; The grains tend not to look like wagon wheels, but rather like honey combs, and that is a big problem because it results in poor mass fraction.</p><p>There have been a couple of more or less successful hybrid applications.&nbsp; Bert Rutan used one.&nbsp; Lockheed also had a successful launch.&nbsp; But they don't seem to be exactly taking over the world and I think that they never will.</p><p>Hybrids are nice for academic work, largely because you don't have to work with explosive materials.&nbsp; So you will probably see ongoing work in university laboratories.&nbsp; </p><p>In my opinion you will see conventional solids, perhaps with a bit better propellant than what is used in shuttle SRBs, used to provide a lot of initial thrust and momentum and more sophisticated liquids used for the upper stages and space engines.&nbsp; I think nuclear thermal propulsion is a long-term winner for deep space propulsion and nuclear powered ion drives will eventually be the ticket for very hight Isp deep space propulsion.&nbsp; Within range of the sun electric propulsion in the form of arc jets will continue to have applications for relatively low thrust but high efficiency applications.</p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

<p>

You don't get to refuel hybrids like you do a liquid.&nbsp; They still have an ablative insulator,&nbsp; And if you use a composite case, like almost all rocket motors except the shuttle SRBs, you won't be able to wash them out re-insulate and cast new propellant.....</p><p>I was thinking more along the lines of casting the propellant in an ablative casing and then loading that into a composite tube. Done in segments it would be easily transported and what remained of the casing could be removed and recycled once the first stage returned.&nbsp;</p><p>The main advantage I see to hybrids is throttleability and the added safety of shutting off the oxidizer if a problem occurs in the motor. I also think using more environmentally favorable components make a lot of sense. While solids provide relatively low ISP they provide a lot of thrust to get off the ground and offer a more compact configuration then liquid tanks and engines would have. </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;What would insulate the casing, unburned propellant in the standard method serves this purpose.&nbsp; What supports the grain in the center, the propellant is bonded to the case in the standard method. <br /> Posted by Cygnus_2112</DIV></p><p>&nbsp;</p><p>Insulate with whatever htpb, ceramics. Holding the fuel grain in place by attachment to the distal end, and</p><p>depending on length, suport rods to the inner surface of the case.</p><p>&nbsp;</p><p>My main point was to see how it burns. To understand the burning characteristics of varies shapes.</p><p>I am here for&nbsp; brainstorming, fun, some education, and to be with others who have a passion</p><p>for space travel and exploration. Not to design and make a rocket.</p>

 

[Cygnus_2112]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Insulate with whatever htpb, ceramics. Holding the fuel grain in place by attachment to the distal end, anddepending on length, suport rods to the inner surface of the case.&nbsp;My main point was to see how it burns. To understand the burning characteristics of varies shapes.I am here for&nbsp; brainstorming, fun, some education, and to be with others who have a passionfor space travel and exploration. Not to design and make a rocket. <br /> Posted by spacy600</DIV></p><p>&nbsp;</p><p>My point is that doesn't matter how is burns,&nbsp; it is not practical, because of those issues.&nbsp;</p>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>.Also, even if the work at Stanford cracks the combustion issues associated with pressure oscillations, you still have to contend with low mass fraction and the complexity of providing an oxidizer that is not integrated with the fuel.&nbsp; I have a hard time seeing how that is in any way superior to even a simple liquid system, say kerosene/LOX.</DIV></p><p>aren't pressure oscillations a problem in all rockets?</p><p>I keep reading about Ares shaking <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-innocent.gif" border="0" alt="Innocent" title="Innocent" width="18" height="18" /></p><p>&nbsp;So the more we learn about boundry layers, pressure oscillations, burn characteristics of various substrates, the better.</p><p>&nbsp;</p>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Personally I don't see hybrids going anywhere.&nbsp; They have been the subject of a low level of R&D for many years.&nbsp; The benefits simply don't compensate for the problems.&nbsp; The grains tend not to look like wagon wheels, but rather like honey combs, and that is a big problem because it results in poor mass fraction. &nbsp;&nbsp;</p><p> In my opinion you will see conventional solids, perhaps with a bit better propellant than what is used in shuttle SRBs, used to provide a lot of initial thrust and momentum and more sophisticated liquids used for the upper stages and space engines.&nbsp; I think nuclear thermal propulsion is a long-term winner for deep space propulsion and nuclear powered ion drives will eventually be the ticket for very hight Isp deep space propulsion.&nbsp; Within range of the sun electric propulsion in the form of arc jets will continue to have applications for relatively low thrust but high efficiency applications.&nbsp; <br /> Posted by DrRocket</DIV></p><p>&nbsp;</p><p>With more understanding of chemistry at the subatomic scale, and nanotech, I think we can understand, and overcome the problems. The paraffin grain at Stanford was a single port.</p><p>&nbsp;</p>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;My point is that doesn't matter how is burns,&nbsp; it is not practical, because of those issues.&nbsp; <br /> Posted by Cygnus_2112</DIV></p><p>&nbsp;</p>rules of brainstorming applies

 

[Cygnus_2112]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;rules of brainstorming applies <br /> Posted by spacy600</DIV></p><p>&nbsp;which was done decades ago and documented. &nbsp; This isn't new technology </p>

 

[spacy600]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;which was done decades ago and documented. &nbsp; This isn't new technology <br /> Posted by Cygnus_2112</DIV></p><p>&nbsp;</p><p>Why is the tour de France not raced with a penny farthing?</p><p>It is always good to look back at old ideas with new eyes.</p><p>New understanding of fluid dynamics, new materials, Nanotech</p><p>Old ideas, new process, materials equal a better, improved product. <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" width="18" height="18" /></p>

 

[Cygnus_2112]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Why is the tour de France not raced with a penny farthing?It is always good to look back at old ideas with new eyes.New understanding of fluid dynamics, new materials, NanotechOld ideas, new process, materials equal a better, improved product. <br /> Posted by spacy600</DIV></p><p>&nbsp;</p><p>"New understanding of fluid dynamics, new materials, Nanotech, new process, materials " are independent of the shape of the motor grain.&nbsp; </p><p>&nbsp;</p>

 

[vulture4]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>while I share your skepticism about the economics of the re-use of shuttle SRB cases, I know people with a good deal of data who disagree.&nbsp; But they do have a dog in the hunt.&nbsp; Quite a bit of the savings supposedly comes from refurbishment of the thrust vector actuator system, and that is probably real.&nbsp; That system is a fairly sophisticated gs generator powered hydraulic system and extremely expensive.&nbsp; The other thing is that those steel case segments do not grow on trees.&nbsp;&nbsp; I don't think any new ones have been made for quite a while (I might be wrong but I don't think so) and I don't know if the tooling is still in place to make new ones.&nbsp; <br /> Posted by DrRocket</DIV></p><p>Virtually every component of the SRBs has to be disassembled, paint, coatings, and insulation removed, plating blasted off to the bare metal, parts magnafluxed, replated, repainted, reassembled. Hybrids require replacement of the high-pressure case and nozzle, so they are not fully reusable. Their ISP is lower than liquids and they lack the thrust of solids. </p><p>A rocket can only be economically reused if it can be simply refueled and flown again. The last, and only, entirely liquid propelled reusable spacecraft was the X-15. While it was obviously suborbital, there is no engineering constraint that prevents a TSTO from being entirely liquid fueled. For an expendable booster or a military missile that must be kept ready for instant launch, solid fuel is often the logical choice, but a reusable stage that uses solid propellant for anything bigger than separation motors is a waste of money. </p><p>I believe that if NASA had not made the SERIOUS error of cancelling the X-34 and essentially firing Burt Rutan, the pre-eminent aerospace engineer of our time, Rutan would have had enough experience with liquids to have have used them for the SpaceShip. That is the proper role for NASA- to give industry the tools to advance technology. As it was Rutan felt hybrids were the low-risk solution, but once you try to push performance this is not necessarily the case.</p><p>We need to face facts. Human spaceflight is possible but impractical. We need to lower cost by orders of magnitude to make it something more than a stunt. Only fully reusable systems can accomplish this; the cost of all the fuel to put the Shuttle in orrbit is less than 1% of the mission cost. Liquid fuel and oxdizer provide the highest performance and the only route to full reusability.&nbsp;<br /> </p><p>In short, Robert Goddard made a major advance with the first liquid-fuel rocket. Solids or hybrids may save on development cost but will keep operating cost high and limit human spaceflight to a lucky handful for generations to come.&nbsp; </p><p>Just my opinion, thanks for listening.</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You don't get to refuel hybrids like you do a liquid.&nbsp; They still have an ablative insulator,&nbsp; And if you use a composite case, like almost all rocket motors except the shuttle SRBs, you won't be able to wash them out re-insulate and cast new propellant.....I was thinking more along the lines of casting the propellant in an ablative casing and then loading that into a composite tube. Done in segments it would be easily transported and what remained of the casing could be removed and recycled once the first stage returned.&nbsp;The main advantage I see to hybrids is throttleability and the added safety of shutting off the oxidizer if a problem occurs in the motor. I also think using more environmentally favorable components make a lot of sense. While solids provide relatively low ISP they provide a lot of thrust to get off the ground and offer a more compact configuration then liquid tanks and engines would have. &nbsp; <br />Posted by scottb50</DIV></p><p>What you are describing is known as a "cartridge loaded grain".&nbsp; That concept is used in small motors like the Hydra 70 system where perfromance is not a major issue&nbsp;in order to have very low cost.&nbsp; It hurts mass fraction and therefore only makes a bad situation worse for hybrids.&nbsp; Isp for solids is not all that bad, about 264 sec (theoretical) and up to about 300 sec delivered, but the Isp density product is pretty good and the mass fraction for solids is very good.</p><p>Hybrids tend to have a wee bit better Isp, but a lot more complexity and very poor mass fraction.&nbsp; Shutting off the oxidizer is not much of an advantage.&nbsp; If you do that you fall back to the ground.&nbsp; Throttleability in rockets is useful for managing trajectory and managing dynamic pressure,&nbsp; but doesn't do much for emergency situations.&nbsp; You can't shut down and you can't fly back home.&nbsp; Rockets are not airplanes.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[spacy600]

http://www.itam.nsc.ru/users/libr/eLib/confer/ICMAR/2002/part_1/leets.pdf