A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Robert Clark on 28 Mar 2010 08:33 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? 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. As you know you have to have the right mass ratio FOR THE PARTICULAR ISP. Then if the Isp for hydrogen is 1.5 times that of the dense propellants but the weight of the tanks is 3 times worse and the weight of the engines is 2 times worse, then since the tanks and engines make up the predominant part of the dry weight of the vehicle, the dense propellant vehicle wins. Bob Clark
From: hallerb on 28 Mar 2010 08:38 Well a SSTO with a payload capacity of a feather is fine if ALL you want to lift is a feather.:(
From: Marvin the Martian on 28 Mar 2010 12:08 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.
From: Jeff Findley on 29 Mar 2010 10:35 "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. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: hallerb on 29 Mar 2010 10:54
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. |