What about using liqid engines for CEV booster?

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frodo1008

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First of all I would like to go over some points that I consider pertinent to my own ideas on what the boosters of the CEV (or CXV) should be like. <br /><br />One of these points is the argument over the relative safety of liquid vs. solid booster engines. Now let me state right off that the solid booster industry (mainly in the form of Morton Thiokol Corporation) has done a truly remarkable and magnificent job of supplying the very large boosters for the STS system. This is in particular after the Challenger accident, which was NOT entirely their fault (at least the engineers at any rate). However, it will NEVER be possible to make such large solid boosters as safe as liquid engines! No less a great rocket scientist as Wherner Von Braun knew this and insisted that the great Saturn series of rockets be powered by only liquid engines. Well, this is not totally correct, as the Saturn escape tower rocket engine was indeed a solid rocket motor, but it was certainly hoped it would NEVER have to work!! <br /><br />So why would it be safer to use the far more complex liquid engines? Especially as in order to give enough thrust in the booster phase there is usually more than one, thus increasing the complexity even more? <br /><br />One of the reasons for this post (and possible thread) is that the answer to the above question is not known to many on these boards, and I felt it needed clearing up before I go on to my own possible proposal. It is the type of testing of such engines that gives the answer here. The liquids used in liquid engines are homogeneous, that is the same liquids can be used for the testing of the engines that is eventually used for the actual launches by such engines. On the other hand solids are not inherently this homogeneous, and the same solid that is used for a solid engine test is not going to be the same solid used in the actual launch. Once you have tested a solid rocket motor, that motor is history (oh, you might be able to reuse the
 
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nyarlathotep

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Or you could save a ton on development costs, and just licence Energia.
 
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frodo1008

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From other posters, there are no Energia's anymore than there are any more Saturn's. Besides what you are talking about with either the Energia or the Saturn is a Super Heavy Lift Launcher and most of my post was devoted to the launcher for the Apollo like CEV. <br /><br /> The Super Heavy Lift Launcher will already use some 5 SSME's, and also (with no objection from me) at least two of the new five segment SRB's. While there are many services and vehicles that we should be renting or purchasing from the excellent Russian space program, the Energia is not one of them.
 
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frodo1008

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Thank you for the information! I realize that as you are still actively employed you may not be able to comment either pro or con on any such ideas as my own, no problem as I understand the sensibilities of the aerospace industry! <br /><br />Is that 11 total engines or 11 spares? Either way it constitutes a minimum of almost two entire launchers for the CEV. The booster would have 5 engines, and possibly the second stage one engine (although the engine for the seconds stage is a long way from being decided yet from what I understand).<br /><br />Once again, thanks, and any further comments that you can make would be most welcome!
 
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frodo1008

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Sorry, in looking back over my reply to your post I may have sounded harsher than I really wanted to!! I have nothing but respect and admiration for the people of the Russsian space program, they do more with less than just about anybody! <br /><br />However, on another thread someone mentioned that the last Energia along with the Buran was stored in a hanger that had a roof collapse, and was wrecked beyond possible use. <br /><br />Also, as I stated my argument for using only liquid engines for the bssoter for the CEV to carry people into LEO did not apply to any Super Heavy Lift Launcher developed from both the SSME's, and the SRB's.<br /><br />Your comments are also most welcome!!
 
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cuddlyrocket

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The problem is money. You would have to develop a new first stage to replace the SRB.<br /><br />The SRB will only be a danger to the crew if it blows up, which seems pretty unlikely. After all, they strap two of them to every Shuttle. And even if they did, the escape tower would in all likelihood save them.<br /><br />All in all, it seems a great deal of money (and probably delay) for a pretty marginal safety improvement over a system that is already supposedly 10 times safer than the STS.
 
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propforce

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Liquid rocket engines are inherently more complex at the vehicle level than a simple SRB.<br /><br />A vehicle propulsion system must feed the engine the right amount of propellant at the right temperature and pressure. This means a compex series of lines, interconnects and valves. The engine has a particular start sequences in which it's various valves open/ close at different time which means a vehicle computer must interface carefully with the engine controller. The engine must be thermally conditioned properly when it runs cryogenic propellant, this means a complext pre-start engine chilldown sequence hours before engine starts. At the mean time, engine demands lots of helium for its purges and keeping gaseous hydrogen away from oxygen in order to avoid explosion. High pressure pneumatic lines everywhere to enable engine valves to open/close properly. The vehicle must devote a significant volume (tanks) and weight to enable the engine operating as expected.<br /><br />So why choose a liquid rocket engine over solids (SRB)? Safety is the first thing comes to mind. But many have argue, and invariably valid for the RSRM, that SRB has demonstrated to be very reliable rocket before and after ignition. So while the liquid rocket engine offerrs the 'pad-abort' capability, it is a mere incremental gain in safety. Beside, the safety issue becomes less of an issue when only a cargo vehicle is involved. <br /><br />But then why does other expendable launch vehicle (ELV) such as the Delta and Atlas still choose liquid rocket boosters? Surely it can not be because liquid is cheaper? Afterall, one must build tanks, lines, and valves, in addition to an engine, then assemble them all together in stead of just buy a SRB !! Why subject yourself to all these complex and costly hardware???<br /><br />Peformance. Liquid rocket engines simply give a much higher payload performance to orbit, even at first stage, assuming you size the correct thrust level. It's highly dependen <div class="Discussion_UserSignature"> </div>
 
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tomnackid

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What about them?<br /><br />But seriously, NASA is not going to put manned space exploration on hold while it develops exotic new technology. I have no doubt that NASA will continue to explore such exotic propulsion ideas as pulse detonation engines, laser launch systems, tethers, scramjets, etc. They have to, its part of their mandate. These technologies will be researched and developed to a point where they show promise for national defense or commercial use then it is up to others to do what they will with them. <br /><br />As far as NASA's mandate to conduct manned space exploration goes they have decided to do this by maximizing the use of already mature technology. I don't see a problem with this. Even though part of NASA's job is to develop cutting edge technology that doesn't mean they have to use it for everything they do. In fact for exploration tried and true is often far superior to cutting edge. Compare Scott's disastrous expedition to the south pole using the height of early 20th century British technology with Amundsen's successful journey using thousand year old Inuit technology.
 
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najab

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><i>But then why does other expendable launch vehicle (ELV) such as the Delta and Atlas still choose liquid rocket boosters? Surely it can not be because liquid is cheaper?</i><p>Beacause the Government (US or Russian) paid to develop them - most commonly to lob nuclear warheads at each other - and Government contractors rarely choose the cheapest option when working on cost-plus projects.</p>
 
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propforce

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That maybe true with Atlas II and Delta II but not so with the EELVs anymore <img src="/images/icons/smile.gif" /><br /><br /> <div class="Discussion_UserSignature"> </div>
 
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najab

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Oh, true. The Atlas 5 and Delta 4 were (largely) paid for by the Government to launch spysats at the Russians instead of nukes.
 
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propforce

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OK if you insist on that argument...<br /><br />.. so tell me, why does SpaceX choose liquid rocket engines instead of solids? <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>
 
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barrykirk

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ISP is not the only factor in the rocket equation. It is an important fact, but it is by no means the whole story.<br /><br />Ion engines have a substantially higher ISP than the SSME yet no one would even think about using an Ion engine, (with present day technology ) for launch into LEO.<br /><br />I'll give two examples here,<br /><br />Falcon 9 rocket Fuel is LOX/RP-1<br /><br />Payload to LEO is 8700 Kg<br />Launch Mass is 291000 kg <br />Payload mass fraction is 3%<br />Cost is $35million<br /><br />The figures I have are for the one with the larger fairing<br />for the smaller fairing the payload to LEO is 9300KG and the cost is $27 million, I didn't use that one as an example because I don't have the launch mass.<br /><br />But assume the launch mass is the same for the two fairing diameters. I suspect it would be lower for the lower fairing diameter.<br /><br />Than the lower fairing diameter has<br /><br />Payload mass is 9300Kg<br />Payload mass fraction of 3.2%<br />Cost of $27 million<br /><br />Note that if the launch mass is lower for the lower fairing diameter version which I suspect than the payload mass fraction will be higher.<br /><br />Delta IV Medium rocket Fuel is LOX/LH2<br /><br />Payload to LEO is 8600 Kg<br />Launch Mass is 249,500 kg<br />Payload mass fraction is 3.45%<br />Cost is $133 Million<br /><br />So for almost 5 times the cost you get a lot less mass to orbit using a more advanced fuel with a higher ISP.<br /><br />The higher ISP does increases the mass fraction by 0.25%, or a gain of 7%.<br /><br />How about rockets using different fuels on different stages? Well, there is a place for solids and low ISP liquids like kerosene. The first stage. Remember that the earlier in the mission the fuel is burned, the less energy was invested to get the fuel to that altitude and velocity.<br /><br />Von Braun who was a genius understood that the ISP of the first stage fuel was not that critical. He used Kerosene for the first stage of the Saturn.<br /><br />Or to put it ano
 
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tap_sa

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<font color="yellow">"So for almost 5 times the cost you get a lot less mass to orbit using a more advanced fuel with a higher ISP. "</font><br /><br />A paper rocket by lean private start-up versus pork booster by long-time government contractor, propellant choice has little to do with the cost difference <img src="/images/icons/rolleyes.gif" />
 
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nyarlathotep

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The Delta IV family is so pricey because of their low fly rates. At high volumes, Boeing could likely get the cost down to less than half that.
 
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propforce

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Two things:<br /><br />1) You are comparing a mature, demonstrated, and reliable launch vehicle with something nothing more than a salesman's pipedream at this time ??? <img src="/images/icons/laugh.gif" /><br /><br />2) No where in my post did I mention launch price, that's a whole discussion by itself, among other thing is what the market can charge. For example, comparing a goverment contractor (in this case, Boeing) launching goverment spy satellites vs. commercial launch services offerred by the Russians or the Chinese. You maybe willing to sacrifice launch reliability for price, if you are a commerical satellite provider.<br /><br />What you need to do is to compare launch vehicles that have <br /><br />1) similar initial launch mass<br />2) similar engine thrust at take off<br />3) compare payload to LEO vs. 1st stage engine Isp<br /><br />Ideally, both vehicles have the same propellant for the 2nd stage so we're comparing the pros & cons of 1st stage propellant choice. Now do that for SRB, Hypergolics, Kerosene/LOX, and LH2/LOX. <br /><br />Now I know these data can be hard to come by, so let's do the next closest thing - compare LVs with similar LEO payload capability. For example, Falcon I versus the Minotaur. <br /><br />P/L to LEO: Falcon I = 670 kg, Minotaur = 640 kg<br />Launch Mass: Falcon I = 27,000 kg. Minotaur = 36,000 kg<br />Propellant: Falcon I = LOX/RP. Minotaur = SRB<br />Engine Thrust: Falcon I = 38,000 kgf. Minotaur = 73,000 kgf.<br />Engine Isp (vac): Falcon I = 310 sec. Minotaur = 260 sec.<br /><br />Now "stretch" the Falcon I propellant tank so that the total launch mass is the same as the Minotaur, how much <i>more</i> payload can it gain ? Then "upgrade" Falcon I's engine to 73,000 kgf and see additional payload performance gain? Now "switch" Falcon I fuel to LH2, with engine Isp goes from 310 to 410, with the same launch mass. How much more LEO payload do you gain?<br /><br />The bigger difference between the engine Isp, e.g., SRB vs. LOX/ L <div class="Discussion_UserSignature"> </div>
 
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barrykirk

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Actually,<br /><br />The Falcon 1 only has 570Kg to LEO not 670Kg. Unless spacex adjusted there numbers but forgot to adjust their website. Also, you claim 38,000 Kgf liftoff when the website claims about 35,000 Kgf<br /><br />OK but let's compare apples to apples.<br /><br />I agree that high ISP is more important at the upper stages. It's the first stage that is less critical. The Minotaur uses 4 stages and is solids all the way to orbit.<br /><br />The falcon 1 uses 2 stages and is LOX/RP-1 all the way to orbit.<br /><br />Now "stretch" the Falcon I propellant tank so that the total launch mass is the same as the Minotaur, how much more payload can it gain ?<br /><br />Well the thrust is 77,000 LBS so increasing the mass to 79,200 LBS is going to mean the rocket will sit on the pad until it burns off 2,200 LBS of propellant. Yes the payload will go up, but not by much.<br /><br />Adding a second Merlin engine with more propellant to get 36,000Kg launch mass. I would expect that the structure will have to be a little beefier to handle the higher Max-Q since she accelerates a lot quicker in that configuration.<br /><br />I'm sure that would increase the payload capacity although I have no idea by how much.<br /><br />Now "switch" Falcon I fuel to LH2, with engine Isp goes from 310 to 410, with the same launch mass.<br /><br />Yes, the ISP went up so the fuel is more efficient. But keeping the mass the same. You realize the engine will get heavier to keep the thrust the same and the fuel tank will get larger and heavier because hydrogen is less dense than RP-1. I would expect the mass to LEO to go up but not as much as you would think. Remember that you are now carrying less fuel and more rocket.<br /><br />Since the fuel is more efficient, the rocket mass will decrease slower. The falcon 1 as it exists probably won't accelerate off the pad that quickly. It wasn't a performance optimized design, but rather the cheapest way to get a tiny payload to orbit. The falcon 1 as it e
 
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najab

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Why liquid engines instead of solids for EELV and SpaceX? Two reasons come to mind: (a) flexibility - you can change a liquid booster's flight profile much easier than you can a solid; and (b) perception - both the EELV and Falcon have been designed with the notion that they might be used for manned launches firmly lodged in the background and, as we all know, you don't launch men on solid rockets!
 
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Swampcat

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<font color="yellow">"...you don't launch men on solid rockets!"</font><br /><br /><img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"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."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>
 
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nyarlathotep

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Dont forget logistics. Solids are too damn heavy to transport and erect cheaply and quickly. Fast turnaround was part of the defence department's requirements for both vehicles.
 
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cuddlyrocket

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Errr... I thought preparing the rockets for launch quickly and cheaply was one of the prime reasons the military went for solid rockets in their ICBMs and SLBMs?
 
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tap_sa

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But we are talking about EE<b><i>LV</i></b>s ie. orbital vehicles, not missiles. LVs with ~8 tonnes or bigger payloads. A solid LV delivering that much payload would be <i>huge</i>.
 
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drwayne

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Actually, most modern mobile ICBM's are in fact solid fueled, because they are transportable, and erect and launch quickly.<br /><br />Solids also have the advantage from a military perspective of being rapid burning, getting them up and out of harms way quickly.<br /><br />Note that I am just talking about the military, ICBM perspective, which is not, strictly speaking, on topic.<br /><br />Wayne<br /> <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>
 
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