A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: J. Clarke on 29 Mar 2010 11:21 On 3/29/2010 10:35 AM, Jeff Findley wrote: > "Marvin the Martian"<marvin(a)ontomars.org> wrote in message > news:KMednS79l_rYcDHWnZ2dnUVZ_joAAAAA(a)giganews.com... >> On Sun, 21 Mar 2010 17:40:19 -0400, Greg D. Moore \(Strider\) wrote: >>> Because 50,000 feet gets you above the bulk of the atmosphere which >>> provides a decent bonus. >> >> Its trivial. If you knew anything about the subject, you wouldn't have >> said that. > > Launching from 50k feet gets you above enough of the atmosphere that you can > optimize your rocket engine for vaccuum. This gives you quite a bit more > ISP than the same engine with a sea level optimized nozzle. The difference > here is that your overall stage performance goes up *over the entire flight > of the stage* due to the higher ISP of the engine. > >> All these people who think that they're so damned smart with all their >> cockeyed ideas, as if they've never been looked at before. > > These aren't "cokeyeyd" ideas. If you knew *anything* about aerospace > engineering, you'd understand. What I understand is that Beltway Bandits will do *anything* for a contract.
From: J. Clarke on 29 Mar 2010 11:24 On 3/29/2010 10:54 AM, hallerb(a)aol.com wrote: > On Mar 29, 10:35�am, "Jeff Findley"<jeff.find...(a)ugs.nojunk.com> > wrote: >> "Marvin the Martian"<mar...(a)ontomars.org> wrote in messagenews:KMednS79l_rYcDHWnZ2dnUVZ_joAAAAA(a)giganews.com... >> >>> On Sun, 21 Mar 2010 17:40:19 -0400, Greg D. Moore \(Strider\) wrote: >>>> Because 50,000 feet gets you above the bulk of the atmosphere which >>>> provides a decent bonus. >> >>> Its trivial. If you knew anything about the subject, you wouldn't have >>> said that. >> >> Launching from 50k feet gets you above enough of the atmosphere that you can >> optimize your rocket engine for vaccuum. �This gives you quite a bit more >> ISP than the same engine with a sea level optimized nozzle. �The difference >> here is that your overall stage performance goes up *over the entire flight >> of the stage* due to the higher ISP of the engine. >> >>> All these people who think that they're so damned smart with all their >>> cockeyed ideas, as if they've never been looked at before. >> >> These aren't "cokeyeyd" ideas. � If you knew *anything* about aerospace >> engineering, you'd understand. >> >> Jeff >> -- >> "Take heart amid the deepening gloom >> that your dog is finally getting enough cheese" - Deteriorata - National >> Lampoon > > Besides with our depency on satellites for everything from TV, to > credit card approval a fast replacement satellite to norbit capacity > is needed. > > KSC was looking to build a facility for just that, with generic > satellites that could be launched from silos within a few days. Nice idea, if "generic satellites" would do all missions. Will they? And who is going to pay to keep them ready? Hint--if DirecTV wanted a generic satellite on a hotpad they'd be paying somebody to do it already. >
From: Marvin the Martian on 29 Mar 2010 12:14 On Mon, 29 Mar 2010 10:35:05 -0400, Jeff Findley wrote: > "Marvin the Martian" <marvin(a)ontomars.org> wrote in message > news:KMednS79l_rYcDHWnZ2dnUVZ_joAAAAA(a)giganews.com... >> On Sun, 21 Mar 2010 17:40:19 -0400, Greg D. Moore \(Strider\) wrote: >>> Because 50,000 feet gets you above the bulk of the atmosphere which >>> provides a decent bonus. >> >> Its trivial. If you knew anything about the subject, you wouldn't have >> said that. > > Launching from 50k feet gets you above enough of the atmosphere that you > can optimize your rocket engine for vaccuum. Repeating the error doesn't refute the fact that it is an error. > This gives you quite a bit > more ISP than the same engine with a sea level optimized nozzle. Generally speaking, that's why second stages are designed differently. > The > difference here is that your overall stage performance goes up *over the > entire flight of the stage* due to the higher ISP of the engine. You're grossly overstating an effect that is not that significant, given that rockets are staged. >> All these people who think that they're so damned smart with all their >> cockeyed ideas, as if they've never been looked at before. > > These aren't "cokeyeyd" ideas. If you knew *anything* about aerospace > engineering, you'd understand. I find that funny as hell. You yourself admit that Boeing studied it. The idea was REJECTED. It was never built.
From: Robert Clark on 29 Mar 2010 12:46 On Mar 28, 12:08 pm, Marvin the Martian <mar...(a)ontomars.org> wrote: > On Sun, 28 Mar 2010 05:33:05 -0700, Robert Clark wrote: > > On Mar 27, 10:33 pm, Marvin the Martian <mar...(a)ontomars.org> wrote: > >> On Sat, 27 Mar 2010 15:24:32 -0700, hall...(a)aol.com wrote: > >> >> The "lack of understanding" would seem to be yours. SSTO *does* > >> >> lower cost, since it eliminates all that pesky 'stacking' and such, > >> >> allowing smaller processing crews. If such a vehicle is also > >> >> reusable (which is different from SSTO) you quickly approach > >> >> airliner cost scales. > > >> > SSTO can only cut costs if the finished product has good weight > >> > capacity > > >> It would require such a large heat shield that it would have very > >> little left for payload. > > >> The SSTO is a dream of people who don't understand the rocket equation > >> who think that going into space should be like driving the family car. > > > Several experts in the field have said single-stage-to-orbit is easy > > to achieve with dense propellants. Yes, EASY. How hard could it be if > > the Titan II first stage had this capability in 1961 without the > > advanced materials available now? > > Then you can go away, stop posting, and get one of the experts who you > let tell you what to think make the case. > > The rocket equation doesn't give a squat about experts, unfortunately. > > delta v = v_e * ln ( m_i/m_f) > > For LEO, delta v => 9.3 km/s > > RP-1 has a I_sp of about 350 seconds, so v_e = 9.8 m/s^2 * 350 s = 3.4 km/ > s > > exp ( (9.3 km/s)/ (3.4 km/s )) = 15.0 > > That means that with RP-1 (kerosene) the initial mass is 15 times the > mass of the empty rocket, or less than 7%. That 7% has to include the > rocket structure, fuel tanks, the pumps to keep the LOX liquid, the > engines and the payload. > > That's just physics. You're not going to be able to change the laws of > physics. > > Easy? Whomever said that is grossly understating the issue, I suspect to > fool ignorant people into funding their projects. There is a reason why > there are no RP-1 single state to orbit rockets. > > > The key point is there are SEVERAL important factors that have to be > > taken into account: the Isp, the thrust/weight ratio of the engines, the > > total weight of the engines, the weight of insulation for cryogenic > > propellants, the weight of the propellant tanks, the complexity of using > > super cryogenic hydrogen as a fuel, etc. Dense propellants are better > > than hydrogen on all these scales except for Isp, and significantly so. > > It very well may be that the mass of the liquid hydrogen tanks, > insulation, and pumps for a liquid hydrogen fuel are bad engineering > solutions for smaller rockets. Large scale works in favor of liquid > hydrogen, since heat loss is related to surface area and large rockets > will have tanks with less surface area per unit mass. Your conclusion in > no way follows from what you state, and your conclusion is wrong in many > cases. > > As far as RP-1 enabling "easy" single state to orbit vehicles, that's > just not so. I am quite willing to accept that the engineering tradeoffs > favor RP-1 for SOME applications. For a disposable SSTO, this is a bad > solution, as staging enables a larger payload. SSTO only makes sense for > a reusable vehicle, and that means re-entry and a larger heat shield for > the larger mass, which means less payload. Actually the propellant for the Titan II first stage was even more dense than kerosene. This allowed it to get a quite high mass ratio of 25 to 1 which means the first stage would have SSTO capability even though the Isp for this propellant was even lower than kerosene, at about 300 s. Believe me, I know what you are saying about hydrogen and it's high Isp. I also had the view before, that a SSTO had to use hydrogen. See for example this earlier post I wrote: Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.energy From: Robert Clark <rgregorycl...(a)yahoo.com> Date: Sat, 6 Sep 2008 14:59:10 -0700 (PDT) Local: Sat, Sep 6 2008 5:59 pm Subject: High strength fibers for hydrogen storage on the VentureStar. http://groups.google.com/group/sci.astro/msg/5253e7e88f49e61f?hl=en However, then I read this paper of John Whitehead, and it hit me like a ton of bricks: Single Stage To Orbit Mass Budgets Derived From Propellant Density and Specific Impulse. John C. Whitehead, Lawrence Livermore National Laboratory. 32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference. Lake Buena Vista, FL July 1-3, 1996 http://www.osti.gov/bridge/servlets/purl/379977-2LwFyZ/webviewable/379977.pdf Whitehead shows that when you consider the other factors such as the weight of hydrogen tanks and the lowered T/W ratio, that the kerosene powered vehicle would be lighter. Or said another way a kerosene vehicle could carry more payload. The higher T/W of dense-fueled engines is familiar, so I'll just refer to the better tankage ratio for the kerosene, though Whitehead discusses both factors. Here is a copied page where Whitehead gives the better tank mass to propellant mass ratio for kerosene than for hydrogen. Note the tankage ratio is 3 times better for kerosene: http://i47.tinypic.com/fuc940.jpg Bob Clark
From: hallerb on 29 Mar 2010 14:16
On Mar 29, 11:24�am, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > On 3/29/2010 10:54 AM, hall...(a)aol.com wrote: > > > > > > > On Mar 29, 10:35 am, "Jeff Findley"<jeff.find...(a)ugs.nojunk.com> > > wrote: > >> "Marvin the Martian"<mar...(a)ontomars.org> �wrote in messagenews:KMednS79l_rYcDHWnZ2dnUVZ_joAAAAA(a)giganews.com... > > >>> On Sun, 21 Mar 2010 17:40:19 -0400, Greg D. Moore \(Strider\) wrote: > >>>> Because 50,000 feet gets you above the bulk of the atmosphere which > >>>> provides a decent bonus. > > >>> Its trivial. If you knew anything about the subject, you wouldn't have > >>> said that. > > >> Launching from 50k feet gets you above enough of the atmosphere that you can > >> optimize your rocket engine for vaccuum. This gives you quite a bit more > >> ISP than the same engine with a sea level optimized nozzle. The difference > >> here is that your overall stage performance goes up *over the entire flight > >> of the stage* due to the higher ISP of the engine. > > >>> All these people who think that they're so damned smart with all their > >>> cockeyed ideas, as if they've never been looked at before. > > >> These aren't "cokeyeyd" ideas. If you knew *anything* about aerospace > >> engineering, you'd understand. > > >> Jeff > >> -- > >> "Take heart amid the deepening gloom > >> that your dog is finally getting enough cheese" - Deteriorata - National > >> Lampoon > > > Besides with our depency on satellites for everything from TV, to > > credit card approval a fast replacement satellite to norbit capacity > > is needed. > > > KSC was looking to build a facility for just that, with generic > > satellites that could be launched from silos within a few days. > > Nice idea, if "generic satellites" would do all missions. �Will they? > And who is going to pay to keep them ready? > > Hint--if DirecTV wanted a generic satellite on a hotpad they'd be paying > somebody to do it already. Generic satellites...... The sats would be designed for long term storage, FAST activation and easy stacking, probably on a silo based booster. This way many companies that MIGHT need a replacement can share the costs. although since many satellites are covered by insurance this may pay for fast replacement. in a critical application the cst although substantial might be trivia in comparison with lost revenues in case of failure. currently much of this is handled by in orbit spares...... both direct tv and dish have multiple sats at each main orbital slot, and usually a older sat just station keeping for redundancy |