A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Jeff Findley on 23 Mar 2010 11:43 "J. Clarke" <jclarke.usenet(a)cox.net> wrote in message news:hoal2d21670(a)news7.newsguy.com... > On 3/23/2010 9:44 AM, Jeff Findley wrote: >> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >> news:ho8ggg0125v(a)news5.newsguy.com... >>> On 3/22/2010 2:37 PM, Jeff Findley wrote: >>>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>>> news:ho8cvh2rfj(a)news6.newsguy.com... >>>>> While I'm not going to give a cite for it, it is generally accepted >>>>> that >>>>> all else being equal a kerosene rocket will have lower specific >>>>> impulse >>>>> than a hydrogen rocket, so whatever performance the X-33 achieves with >>>>> a >>>>> kerosene rocket will be less than for a hydrogen rocket. >>>> >>>> ISP is one measure of engine performance. Vehicle performance is much >>>> more >>>> complicated and depends on many more variables besides engine ISP. In >>>> particular, LH2 isn't very dense. Kerosene is far more dense than LH2 >>>> plus >>>> it doesn't need cryogenic storage. In a vehicle design, kerosene has >>>> some >>>> distinct advantages which may make up for its lower ISP. >>> >>> And those are going to put an X-33 in orbit? >> >> I never claimed they would, > > Then why are you introducing them to this thread? > > <Remainder, with no relevance to the kerosene-fueled X-33 concept snipped> So you want to be able to make sweeping generalizations well beyond the context of the subject line but sill be able to hide behind the subject line when those same sweeping generalizations are shot down? Wow. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: Pat Flannery on 23 Mar 2010 14:56 On 3/23/2010 5:28 AM, Jeff Findley wrote: > But as Henry Spencer said of Atlas in one of his posts: > > More precisely, its first stage could have taken 1-2klb of payload into > orbit all by itself, assuming suitable engines with the same Isp and > engine mass as the standard ones. > > In other words, the stage as flown couldn't be considered an SSTO, but a bit > of development to produce a deep throttling sustainer engine could have made > it an SSTO. Atlas easily had the mass fraction and engine performance > necessary, but it lacked the deep throttling necessary to make it happen. Originally, the Atlas A test version (as the X-11) was just going to use the central sustainer engine, rather than using just the two outer booster engines as was actually flown. > I'm not going to argue that point. But you might want to Google Black > Horse. It's a very interesting concept on which there was extensive number > crunching done. Oh heck, it's interesting enough I'll GIVE you a link: > > http://www.ai.mit.edu/projects/im/magnus/bh/analog.html Robert Zubrin thinks this is a good idea that would be easy to implement; that should warn you right there. > This is the sort of "outside the box" thinking for a (near) SSTO that > doesn't violate physics and relies on the proven technology of in flight > refueling, which is done routinely by the military. Heck, even Air Force > One is equipped to receive fuel via this method. If it's safe enough and > reliable enough for the President of the United State's aircraft, it ought > to be good enough for a launch system! The difference being in the case of Black Horse what it was being tanked up with at altitude was hydrogen peroxide, not jet fuel. Rather than going the aerial refueling route, it would be a lot easier to carry the fully-fueled Black Horse to altitude atop a 747 or C-5B, and air-launch it, or air launch it after fueling it in-flight from internal supplies while still attached to the carrier aircraft. You can then make the landing gear even lighter, as it's now only used for landing with no propellants aboard. Once you do that, Black Horse suddenly becomes very similar to the Air Launched Sortie Vehicle in concept, though strangely needing far less of a propellant load to reach orbit - ALSV needed one or more drop tanks to accomplish this. Take a look at the weight estimates in that article versus the amount of propellant it's supposed to carry; empty weight is 14,958 lbs, ignition for the climb to orbit weight is 184,250 lbs - a mass ratio of 12.3. Atlas had a mass ratio identical to that: http://www.brighthub.com/science/space/articles/29607.aspx ....despite lacking goodies like wings, landing gear, a cockpit, added jet engines, and a TPS...and possessing a shape that was far more efficient for storing propellants in for external area. Even then, it needed to jettison a couple of its engines to make it into orbit. The H2O2/JP-5 propellant combo for Black Horse also has lower isp than the Atlas LOX/kerosene. LOX is pure oxygen rather than a oxygen/hydrogen mixture so you are also getting superior reactive energy storage with it per volume over H2O2, despite the higher density of H2O2 (1.463 g/cm3 vs. 1.141 g/cm3 for LOX). So how is this all supposed to work? The answer is that it doesn't work; the whole thing is a bunch of hooey thrown together out of badly unrealistic mass and performance estimates. Pat
From: J. Clarke on 23 Mar 2010 12:17 On 3/23/2010 11:43 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:hoal2d21670(a)news7.newsguy.com... >> On 3/23/2010 9:44 AM, Jeff Findley wrote: >>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>> news:ho8ggg0125v(a)news5.newsguy.com... >>>> On 3/22/2010 2:37 PM, Jeff Findley wrote: >>>>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>>>> news:ho8cvh2rfj(a)news6.newsguy.com... >>>>>> While I'm not going to give a cite for it, it is generally accepted >>>>>> that >>>>>> all else being equal a kerosene rocket will have lower specific >>>>>> impulse >>>>>> than a hydrogen rocket, so whatever performance the X-33 achieves with >>>>>> a >>>>>> kerosene rocket will be less than for a hydrogen rocket. >>>>> >>>>> ISP is one measure of engine performance. Vehicle performance is much >>>>> more >>>>> complicated and depends on many more variables besides engine ISP. In >>>>> particular, LH2 isn't very dense. Kerosene is far more dense than LH2 >>>>> plus >>>>> it doesn't need cryogenic storage. In a vehicle design, kerosene has >>>>> some >>>>> distinct advantages which may make up for its lower ISP. >>>> >>>> And those are going to put an X-33 in orbit? >>> >>> I never claimed they would, >> >> Then why are you introducing them to this thread? >> >> <Remainder, with no relevance to the kerosene-fueled X-33 concept snipped> > > So you want to be able to make sweeping generalizations well beyond the > context of the subject line but sill be able to hide behind the subject line > when those same sweeping generalizations are shot down? Wow. Again comments with nothing to do with the proposed concept. I bet you're real fun in design reviews.
From: Pat Flannery on 23 Mar 2010 16:15 On 3/23/2010 5:55 AM, Jeff Findley wrote: > > Henry Spencer did the math for several existing rocket stages. What most > needed to make this happen would be a deeply throttlable engine. Atlas was > an example. From memory, one of the Titan II stages and I think one of the > Saturn V stages also had the appropriate mass fraction. Now that you mention it, I seem to remember statements that the Titan II first stage could do this, but with almost no payload aboard. This claims that for it: http://en.wikipedia.org/wiki/Single-stage-to-orbit But also states that it has a mass fraction of 25/1; according to Encyclopedia Astronautica the stage had a mass fraction of 17.5/1: http://www.astronautix.com/lvs/titan.htm From here, it's 23.7/1: http://www.titan2icbm.org/titanD.html That seems awfully high, even given the chem-milled tankage. There was also a proposal for a launcher based on the first stage of the Saturn V, but that one was to jettison the four outer F-1s on the way up: http://www.up-ship.com/drawndoc/sdoc63ad.jpg > If you do the math an expendable SSTO isn't really that hard. Yeah, but the payload is certainly nothing to get excited about, and that right there should have been a warning about reusable ones that need TPS and recovery systems. Pat
From: Pat Flannery on 23 Mar 2010 16:25
On 3/23/2010 6:52 AM, J. Clarke wrote: >> Henry Spencer did the math for several existing rocket stages. What most >> needed to make this happen would be a deeply throttlable engine. Atlas >> was >> an example. From memory, one of the Titan II stages and I think one of >> the >> Saturn V stages also had the appropriate mass fraction. >> >> If you do the math an expendable SSTO isn't really that hard. > > So why are they not in common use? Because of the low payload that they can carry into orbit versus the overall cost of the vehicle. If adding a second stage increases vehicle cost by 75% but allows you to put twice as much weight into orbit, then your price-per-pound into orbit is lower than using a SSTO launcher. Pat |