The single-stage-to-orbit vehicle problems

nec208 · May 2, 2008

While a great idea on paper the X-33 had a lot more problems then building complicated shaped tanks. That it would have worked at all is questionable, even as a small scale demonstrator.The  X-33 was too big and would be like the space shuttle too big = more costly.A smaller x-33 would be a better option.Just like machines, people, animals and plants the key is evolution. What works best dominates and spawns chnages that improve on the initial product. The Shuttle not spawning an offspring makes it an evolutionary dead end. The dinosaurs survive, Delta, Atlas, Soyus, Aerianna are all improved and updated versions of the earliest designs. The shuttle did not spawn do to coast.It is too costly for any evolutionary movement.And it may always be costly to do rockets are very complex. And cars and planes are cheaper =evolution and the same thing for computers and electronics.Shuttle pushed the technology too far too fast. Saturn could have been used to build the ISS and with refinements would probably be launching a runway landing vehicle today. Well coast was not the only thing , the US people want the space program to be just has safe has a airplanes and this is not possible now.Also there alot of people who are anti-space.  <div class="Discussion_UserSignature"> </div>

qso1 · May 2, 2008

While a great idea on paper the X-33 had a lot more problems then building complicated shaped tanks. That it would have worked at all is questionable, even as a small scale demonstrator.Just like machines, people, animals and plants the key is evolution. What works best dominates and spawns chnages that improve on the initial product. The Shuttle not spawning an offspring makes it an evolutionary dead end.I still see it as budgetary. Evolution required millions of years to effect change in species. Changes in design occur in mere decades at most. What the shuttle represents is the key here. The shuttle represents reusable access to space which cannot be provided by the surviving dinos you mentioned. The dinosaurs survive, Delta, Atlas, Soyus, Aerianna are all improved and updated versions of the earliest designs.They survive because they already exist and nobody has to push the technology much to improve them. Pushing the technology entails increased cost in the R&D required. Shuttle pushed the technology too far too fast. Saturn could have been used to build the ISS and with refinements would probably be launching a runway landing vehicle today.I agree, the shuttle was way to big a bite technology wise and the Saturn could have been used to build ISS. In fact, thats what Werhner Von Braun was looking to do through his plan presented to MSFC in 1969. Use Saturn-Vs for heavy lift tasks and small shuttle vehicles to shuttle passengers and small payloads to a completed station. One thing the well over 100 Shuttle flights has done is prove the basic hardware, it seems a shame not to evolve to the next stage and continue the reign of the donosaurs. While Shuttle was designed well beyond it's needs it has proven the core concepts works, the next stage should be looking at the failings in the design and making changes the make it work better, not put it in museums and return to the beginning.This is true. One thing that will evolve from the shuttle. The Ares LVs. I look at current Soyus, Delta and Atlas as 3.0 versions while Shuttle started as 5.0 and is 5.5 now. I would rather see Shuttle 6.0 then 2.5. Posted by scottb50Agree here as well. I guess the only way well see shuttle followed up by a 6.0 version will be if private enterprise/industry can pull it off. I've given up on NASA ever being funded well enough to achieve the feats of Apollo days and beyond.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

qso1 · May 2, 2008

The  X-33 was too big and would be like the space shuttle too big = more costly.A smaller x-33 would be a better option.The X-33 Venture Star was about as small as practical/possible to build as an SSTO and still have useful payload and passenger capacity. There was an image of the scale models of Venture Star the shuttle and another concept based on Delta Clipper. The Venture Star is almost as big as the orbiter. But when you realize all the propellant was aboard the Venture Star, its useful payload and passenger carrying capability is more readily apparent.  The shuttle did not spawn do to coast.It is too costly for any evolutionary movement.And it may always be costly to do rockets are very complex. And cars and planes are cheaper =evolution and the same thing for computers and electronics.Good point here and one that may well stop private enterprise efforts down the line. If this were to prove true, that is both government and private enterprise efforts fail. Then we would end up ackowledging that humanity is not technologically ready to assume regular airliner like operations in space.  Well coast was not the only thing , the US people want the space program to be just has safe has a airplanes and this is not possible now.Also there alot of people who are anti-space.And the anti space ones are generally anti human spaceflight because of cost.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

qso1 · May 2, 2008

No one knows if SSTO is attainable or not with the technology we have. Posted by nec208Good point and one I hope will demonstrate that we can do SSTO by the Blue Origins companies Goddard SSTO vehicle. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

scottb50 · May 2, 2008

The problem is the first stage that has to bear the brunt of the launch. To take it to LEO and return it intact is just not currently possible. Not that it might not be in the future, but right now it isn't.That's the basis of a TSTO, you don't take the first stage to orbit. The only analegy I can come up with is you do what White Knight and and Space Ship One does with the first stage. The second stage goes to LEO. To do that with a commercially acceptable payload takes something in the same class as Shuttle, or even bigger.   <div class="Discussion_UserSignature"> </div>

nec208 · May 4, 2008

Good point here and one that may well stop private enterprise efforts down the line. If this were to prove true, that is both government and private enterprise efforts fail. Then we would end up ackowledging that humanity is not technologically ready to assume regular airliner like operations in space. ----------------------------------------------------------------------------------------------------------------------------------- But if rockets are not advancing do to no research ,  it will not matter  50 years from now ,100 years from now or 200 years from now , will be the same thing.If government or private enterprise are not giving money to do resarch , than there will be no advancing in rockets . If there is no research being done in the US,Canada,UK or China into SSTO or a space plane on a rocket boosters there would be no advancing  in rockets.And it seems the US government does NOT want to do research into SSTO or a space planes .Even bigger space capsule.They are going with old ways that works where they don't have to give much money to do research .Also I must stress no metter what using SSTO ,space planes ,capsule,space station,plane rocket jet combo so on  size and weight is a major problem.Do to coast and the power to take up in space.   <div class="Discussion_UserSignature"> </div>

Swampcat · May 5, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> But if rockets are not advancing do to no research ,  it will not matter  50 years from now ,100 years from now or 200 years from now , will be the same thing.If government or private enterprise are not giving money to do resarch , than there will be no advancing in rockets . If there is no research being done in the US,Canada,UK or China into SSTO or a space plane on a rocket boosters there would be no advancing  in rockets.And it seems the US government does NOT want to do research into SSTO or a space planes .Even bigger space capsule.They are going with old ways that works where they don't have to give much money to do research .Also I must stress no metter what using SSTO ,space planes ,capsule,space station,plane rocket jet combo so on  size and weight is a major problem.Do to coast and the power to take up in space.   Posted by nec208</DIV> nec, research into cheaper methods of getting into space is being done by a growing number of independent private companies and non-profit groups. Whether or not this research bears fruit is yet to be seen as it has not been going on all that long.Keep in mind that government sponsored spaceflight is not a necessity. Without some national security need or other strong economic or political reason for doing it, it is hard to justify spending tax payers money on it. Also keep in mind that NASA is a government agency. They have a large, highly paid work force and entrenched bureaucracy that sucks up a lot of money that could go to other things, like actual research and development. Add to this the cost of war in Iraq and Afghanistan, a shrinking economy and the net result is less money for rocket research. It's a fact of life and no way around it.NASA actually does a lot with the resources they have, despite these problems, but real progress is only going to come when private enterprise gets into the game and figures out how to make a profit from doing it. And they won't get into it in a big way unless there is profit in it.  <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "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."Thomas Jefferson </div>

KosmicHero · May 5, 2008

All, First, 'expellant', the notion that you can recapture some of the propellant that you expelled for reuse IS NOT GOING TO WORK! This violates the fundamental principles of rocketry.Second, DARPA is one of the leading financiers of SSTOs, specifically air-breathing or scramjet engine technology.  The primary technologies for this have quite a bit of national security/defense applications.  You cannot rely on private industry to fund this for two reasons: (1) the current funds held by the so-called 'new space' industry is tiny compared to the R&D costs associated with making either SSTO or TSTO work, and (2) they have no economic incentive to do so.  Shareholders of any of these firms would sell their stock so fast the CEO wouldn't even make it to the press conference.  Last, there are far fewer technical boundaries to spaceflight currently than there are political and financial boundaries.  Given the will and the purse to go explore space, and it would be done.  <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

qso1 · May 8, 2008

All, First, 'expellant', the notion that you can recapture some of the propellant that you expelled for reuse IS NOT GOING TO WORK! This violates the fundamental principles of rocketry.I agree. Second, DARPA is one of the leading financiers of SSTOs, specifically air-breathing or scramjet engine technology.  The primary technologies for this have quite a bit of national security/defense applications.And as such, it could be awhile if ever, that a commercially available unclassified vehicle would emerge. You cannot rely on private industry to fund this for two reasons: (1) the current funds held by the so-called 'new space' industry is tiny compared to the R&D costs associated with making either SSTO or TSTO work, and (2) they have no economic incentive to do so.  Shareholders of any of these firms would sell their stock so fast the CEO wouldn't even make it to the press conference.I agree that private industry lacks sufficient funding capital. That has pretty much always been a showstopper for them. But, none of the above has stopped Bezo's and his Blue Origins efforts so far. And there would be one huge economic incentive beyond space tourism. Being able to access low orbit with a vehicle that can be operated nearly as frequently as an airliner. The one thing still missing is, what to do besides tourism. But I suspect the "What to do" will solve itself if Private industry can succeed and much of that will be services geared towards supporting tourism. Last, there are far fewer technical boundaries to spaceflight currently than there are political and financial boundaries.  Given the will and the purse to go explore space, and it would be done. Posted by KosmicHeroI agree here but I would say that there are still technical boundries. After all, NASA was unable to overcome technical boundaries that may or may not be the result of insufficient funding. The Venture Star problems may be insurmountable regardless of funding but we won't know for certain since it was canceled largely because of funding problems that resulted from a seemingly insurmountable technical problem.But now combine government (NASA) inability to do much with SSTO, with your reasons for private industry not being able to do it...doesn't leave much incentive for man in space at all. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

scottb50 · May 10, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Second, DARPA is one of the leading financiers of SSTOs, specifically air-breathing or scramjet engine technology.</DIV> The problem is scramjets and other air-breathers are worthless as a way to get to LEO. What I have proposed uses turbojets initially, but they would only run for about a minue and a half and primarily be used to offset the weight of themselves and their propellant. Beyond that you need a rocket engine, pure and simple.Scramjets and such, just don't fit into the operation. Big rocket engines and solid motors, combined with the offset of the turbojet thrust is one thing, but to have to accellerate to a speed a scramjet could be used, being dead weight to that point, is rediculous. By then it would operate for a very short time and require a zoom climb to orbit. It's a waste of resources to even think about it.The only way I could see it working is having rockets and turbojets for lift off, the turbojet and rockets shut off at 50,000 feet, or so, and scramjets drive the vehicle horizontally to gain speed. Rockets would then have to re-ignite to reach orbit. From lift off the scramjets are dead weight, they just don't make much sense.Turbojets would be used for landing and cross-range capability as well as carrying their own weight at lift off, then it becomes a simple problem of rocket motors and propellant. Which isn't really that simple. SSTO may very well be possible in the future, fully re-usable TSTO is possible now. It might be better to go with what works just to get it done and build on that then going for the Gold from the beginning. I would love to have a Bently Coupe, but my Hyundi gets me were I want to go, maybe where it gets me will allow me to get the Bently.  <div class="Discussion_UserSignature"> </div>

qso1 · May 10, 2008

IIRC, scramjet proposals normally incorporate turbojets for initial takeoff because the scrams cannot be used until the craft achieves velocities above mach 1. Rocket engines would have to be extremely robust to be operated continuously and ideally, one should keep the number of differing propulsion systems to an absolute minimum to avoid high costs. That is...if you do utilize a rocket...do either liquid or solid but not both and for this application, I think liquid has advantages over solids.But ultimately, in our funding starved aerospace environment, I tend to agree more with your idea of TSTO development.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

scottb50 · May 11, 2008

Scramjet proposals normally incorporate turbojets for initial takeoff because the scrams cannot be used until the craft achieves velocities above mach 1. Rocket engines would have to be extremely robust to be operated continuously and ideally, one should keep the number of differing propulsion systems to an absolute minimum to avoid high costs......Absolutely, reality is; the weight of engines and the weight of their fuel, fuel containers, as well as structure dedicated to attaching them to the rockets, they might, I'm not that clear on it yet, carry their own weight.  Scram jets just would add more weight, if they run for seconds are they really don't contribute to the program. They are not needed tp get down, slowing is the problem not going faster   It's like wings don't do you any good in Space, neather do Scramjets and all those other jets. The idea is to get above the atmosphere and accelerate, well above the altitude any of those jets would be nothing more then adding dead weight dead weight. You still need liquid rockets.  It takes a rocket, or rocket engines any way you look at it. It would take more then forty of the most powerful commercially available jet engines, just to get a Shuttle to a hover. Obviously we need a better way. Two of those power the 787, add Scram jets and they only work the other way, dead weight off the pad, used for less then a minute, before they blow out.  ..That is...if you do utilize a rocket... either liquid or solid but not both and for this application, I think liquid has advantages over solids......If the solid can be kept big, and powerful, the shell and re-usable propellant containers would be dead weight once it is empty, but shortly after the Solids, and liquids, run out you are at an altituded to release the Upper Stage and return the First Stage for re-use anyway..Which is the main reason the First Stage has return capabilities. The empty solid Modules weigh a little more then  what the liquid fuel modules weigh, being empty of propellant. With the Module carrying the loads a very light outer surface can also be used. 60,000 feet or even slightly higher would take minimal thermal protection. It's a simple matter of scaling the system. I would start with Common Cores, for about double the Shuttle payload I would use Six Modules, four liquid and two solids. Two liquids and two solids would also be use for smaller paylads. Even a single liquid and two solids could launch nano- technology. With the outer surface simply attached to the Modules it would be rateher light. <div class="Discussion_UserSignature"> </div>

j05h · May 11, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Pretty much this whole discussion points out that SSTO is not attainable with known technology.... No one knows if SSTO is attainable or not with the technology we have.It has not got the funding that the army gets and the time doing resarch .Well weight and size is a big problem do to coast and enormous power to get it in space.And SSTO is a a very big challenge and if they do fix it ,DO NOT  count on any thing big.If you want rocket evolution get DARPA running it and do away of NASA . Posted by nec208</DIV> SSTO is entirely possible and been demonstrated in a flying rocket stage: IIRC the Saturn S-1C (or IIB?) had appropriate mass fraction and thrust to make orbit alone. No payload, of course, but SSTO is within engineering reality. Is SSTO within economic or govt-cost-plus reality now? Probably not, but there is no need for it anyway. The best option for SSTO is launching extremely small and light crew-exchange craft, a market/need that Soyuz currently owns. Optimizing production and finding economies-of-scale in current rockets is the most likely  path to affordable spaceflight.If by SSTO you meant reusable and quick-turn-around in a single package, no, that is not within the realm of engineering yet. For example, NASA couldn't even make Single-Stage-To-Montana work in the X-33. The old NASP/Orient Express scramjet also proved unbuildable. Why? It is because space is hard and different. If you want reusable, airliner-style operation the vehicle is going to be vastly different than either capsule-on-rocket or spaceplane+boosters. It might be a laser-launched disc, or 500-ton to LEO Ultra Heavy Lift (putting the economy-scaling into each vehicle like a cargo ship) or even the insane multiple-docking 32 craft biamese design Jon Goff analyzed recently.  DARPA is focusing on responsive-lift, generally as an evolution of standard multistage rockets. DARPA and DoD have a larger budget for space than NASA, but it's mostly spy-sats and research (and perhaps the occasional trans-atmospheric spaceplane).A quote from Henry Spencer:  "Ah, but remember the key point the BDB crowd make: enlarging the vehicle (not adding more pieces to an existing vehicle, but making the pieces of a new design bigger) costs almost nothing. If you don't like the size of the payload, just make the launcher bigger. Costs scale primarily with parts count, thinness of margins, and nearness to the leading edge of technology, but only very weakly with size."Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

annodomini2 · May 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> Scramjet proposals normally incorporate turbojets for initial takeoff because the scrams cannot be used until the craft achieves velocities above mach 1. Rocket engines would have to be extremely robust to be operated continuously and ideally, one should keep the number of differing propulsion systems to an absolute minimum to avoid high costs......Absolutely, reality is; the weight of engines and the weight of their fuel, fuel containers, as well as structure dedicated to attaching them to the rockets, they might, I'm not that clear on it yet, carry their own weight.  Scram jets just would add more weight, if they run for seconds are they really don't contribute to the program. They are not needed tp get down, slowing is the problem not going faster   It's like wings don't do you any good in Space, neather do Scramjets and all those other jets. The idea is to get above the atmosphere and accelerate, well above the altitude any of those jets would be nothing more then adding dead weight dead weight. You still need liquid rockets.  It takes a rocket, or rocket engines any way you look at it. It would take more then forty of the most powerful commercially available jet engines, just to get a Shuttle to a hover. Obviously we need a better way. Two of those power the 787, add Scram jets and they only work the other way, dead weight off the pad, used for less then a minute, before they blow out.  ..That is...if you do utilize a rocket... either liquid or solid but not both and for this application, I think liquid has advantages over solids......If the solid can be kept big, and powerful, the shell and re-usable propellant containers would be dead weight once it is empty, but shortly after the Solids, and liquids, run out you are at an altituded to release the Upper Stage and return the First Stage for re-use anyway..Which is the main reason the First Stage has return capabilities. The empty solid Modules weigh a little more then  what the liquid fuel modules weigh, being empty of propellant. With the Module carrying the loads a very light outer surface can also be used. 60,000 feet or even slightly higher would take minimal thermal protection. It's a simple matter of scaling the system. I would start with Common Cores, for about double the Shuttle payload I would use Six Modules, four liquid and two solids. Two liquids and two solids would also be use for smaller paylads. Even a single liquid and two solids could launch nano- technology. With the outer surface simply attached to the Modules it would be rateher light. Posted by scottb50</DIV> I agree that carrying multiple engines for one specific job renders extra unnecessary weight, however there are other proposals which theoretically combine the capabilities of multiple engines such as: http://www.reactionengines.co.uk Now LACE engines are not new and they have been done before, this is the only proposal for an SSTO that looks realistic.  <div class="Discussion_UserSignature"> </div>

keermalec · May 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>A quote from Henry Spencer:  "Ah, but remember the key point the BDB crowd make: enlarging the vehicle (not adding more pieces to an existing vehicle, but making the pieces of a new design bigger) costs almost nothing. If you don't like the size of the payload, just make the launcher bigger. Costs scale primarily with parts count, thinness of margins, and nearness to the leading edge of technology, but only very weakly with size."</DIV> JO5H, I think Spencer means cost per unit mass scales primarily with parts count... not cost itself. If you make a rocket twice as big, the cost per kg is going to remain substantially unchanged, it may probably even decrease. But the overall cost will most definetely increase, probably by a factor of just under two.Replying to: <DIV CLASS='Discussion_PostQuote'>STO is entirely possible and been demonstrated in a flying rocket stage: IIRC the Saturn S-1C (or IIB?) had appropriate mass fraction and thrust to make orbit alone.</DIV>By Saturn 1-C do you mean the Saturn SSTO? If so, this unfortunately never came near to production. Reasons for abandonning the project are not clear but I would guess they have to do with re-entry. If a typical re-entry capsule needs to dedicate 15% of its mass to an aeroshell, then clearly SSTO is not possible. Considering 4% for structure, 3% for engines and tanks, and 3% for payload, that means "only" 75% of the inital mass is left for propellant. Using the rocket equation with highest acheivable isp today (466 seconds) gives a final velocity of only 6.3 km/s. clearly insufficient for reaching LEO. Using the Rocket Equation in reverse, in order to achieve 10 km/s, the propellant mass must be at least 88.8% of GLOW (Gross Lift-Off Weight). Reserving 10% for structure, engines, tanks and payload, that means your re-entry TPS (Thermal Protection System) must weigh less than 1.2% of GLOW.In my view the key to designing a re-usable single stage to orbit vehicle is developing a (very) lightweight aerobraking system: parafoil, inflatable aeroshell, ballute, high-altitude parachute, parashield? ThereIwas has done some good research on ballutes I remember. <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /> <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

DrRocket · May 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>...In my view the key to designing a re-usable single stage to orbit vehicle is developing a (very) lightweight aerobraking system: parafoil, inflatable aeroshell, ballute, high-altitude parachute, parashield? ThereIwas has done some good research on ballutes I remember. Posted by keermalec</DIV>You have your finger on the problem.  But rather than a lighter braking system, how about higher Isp ?  You can approach that problem  in a couple of ways.  One is use of air breathers.  If you don't have to carry your oxidizer with you then you can achieve much higher Isp.  The obvious disadvantage is you can only use one where there is some air.  So-called multi-mode engines have been considered.   But there are some real problems there.The other way is more conventional.  As has been pointed out elsewhere the primary drivers of Isp are temperature and molecular weight.  If one could use advanced materials to permit engine operation at higher temperatures, then using something like hydrogen for a working fluid offers the potential for Isp of over 1000s, and perhaps quite a bit beyond  depending on the specific technology.  This sort is Isp is actually realized in existing engines, arc jet and ion drive come to mind, but the thrusts are at present tiny, and not close to suited for launch from Earth -- even with high Isp you need a thrust to weight ratio greater than 1.  Nuclear propulsion, probably with hydrogen as the working fluid, may also supply comparable Isp, but there is a lot of work to be done to make it practical and political problems to be overcome.This point of view has come in the past during kickoff efforts for SSTO programs.  I believe that someone from Boeing once gave a pitch that basically said if you really want to work on SSTO go find anothere 100s of ISP (I wasn't at the meeting but I was doing some technology planning with someone who was).  That is probably a very good idea, but not popular because of the difficulty involved, because you are nowhere near ready to start designing an actual vehicle,  and because the money would go somewhere other than where the advocates of the time want it to go. <div class="Discussion_UserSignature"> </div>

scottb50 · May 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>You have your finger on the problem.  But rather than a lighter braking system, how about higher Isp ?  You can approach that problem  in a couple of ways.  One is use of air breathers.  If you don't have to carry your oxidizer with you then you can achieve much higher Isp.  The obvious disadvantage is you can only use one where there is some air.  So-called multi-mode engines have been considered.   But there are some real problems there.The other way is more conventional.  As has been pointed out elsewhere the primary drivers of Isp are temperature and molecular weight.  If one could use advanced materials to permit engine operation at higher temperatures, then using something like hydrogen for a working fluid offers the potential for Isp of over 1000s, and perhaps quite a bit beyond  depending on the specific technology.  This sort is Isp is actually realized in existing engines, arc jet and ion drive come to mind, but the thrusts are at present tiny, and not close to suited for launch from Earth -- even with high Isp you need a thrust to weight ratio greater than 1.  Nuclear propulsion, probably with hydrogen as the working fluid, may also supply comparable Isp, but there is a lot of work to be done to make it practical and political problems to be overcome.This point of view has come in the past during kickoff efforts for SSTO programs.  I believe that someone from Boeing once gave a pitch that basically said if you really want to work on SSTO go find anothere 100s of ISP (I wasn't at the meeting but I was doing some technology planning with someone who was).  That is probably a very good idea, but not popular because of the difficulty involved, because you are nowhere near ready to start designing an actual vehicle,  and because the money would go somewhere other than where the advocates of the time want it to go. Posted by DrRocket</DIV>A multifunction engine could be done, but wether it would be worth the weight become the question. You would need block the fan bypass to make it a pure jet and reopen them when you convert to a Ramjet. A big turbofan for takeoff converted to a pure jet with an afterburner that becomes the combustion chamber for a Ramjet and finally a rocket motor. The problem is it would need mechanical doors, a movable inlet and variable nozzles, both in use for years on military equipment, it then becomes a problem of is the weight worth it.If you start with the most powerful turbofan, say a GE90 of 115,500 pounds thrust, four would allow a takeoff weight of 1.5 million pounds, figure and empty weight of 300,000 pounds or 1.2 million in payload and propellant. The turbofans are rated at about 1.8lb/perlb of thrust so takeoff to say 30,000 feet would use roughly 80,000 pounds of fuel, converted to an afterburning jet it would probably need close to the same to get to ramjet speeds. Then theres the rocket, let's say 200,000 pounds so far.We then need to accelerate from about M-7 to orbital speed once outside the atmosphere. This would take basicaly the same power the Shuttle has say 500,000 pounds of LOX would be needed. Using kerosene for the whole thing would probably save weight, but it would be hard to get that much power out of a kerosene/LOX motor. Hydrogen would be better, but you would still need at least twice what the Shuttle carries. 500,000 pounds of Hydrogen and the same of LOX, plus structure more structure then with kerosene and you have very little payload.  <div class="Discussion_UserSignature"> </div>

annodomini2 · May 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>A multifunction engine could be done, but wether it would be worth the weight become the question. You would need block the fan bypass to make it a pure jet and reopen them when you convert to a Ramjet. A big turbofan for takeoff converted to a pure jet with an afterburner that becomes the combustion chamber for a Ramjet and finally a rocket motor. The problem is it would need mechanical doors, a movable inlet and variable nozzles, both in use for years on military equipment, it then becomes a problem of is the weight worth it.If you start with the most powerful turbofan, say a GE90 of 115,500 pounds thrust, four would allow a takeoff weight of 1.5 million pounds, figure and empty weight of 300,000 pounds or 1.2 million in payload and propellant. The turbofans are rated at about 1.8lb/perlb of thrust so takeoff to say 30,000 feet would use roughly 80,000 pounds of fuel, converted to an afterburning jet it would probably need close to the same to get to ramjet speeds. Then theres the rocket, let's say 200,000 pounds so far.We then need to accelerate from about M-7 to orbital speed once outside the atmosphere. This would take basicaly the same power the Shuttle has say 500,000 pounds of LOX would be needed. Using kerosene for the whole thing would probably save weight, but it would be hard to get that much power out of a kerosene/LOX motor. Hydrogen would be better, but you would still need at least twice what the Shuttle carries. 500,000 pounds of Hydrogen and the same of LOX, plus structure more structure then with kerosene and you have very little payload.  Posted by scottb50</DIV> Read up on Liquid Air Cycle Engines(LACE Rocket) <div class="Discussion_UserSignature"> </div>

scottb50 · May 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> Read up on Liquid Air Cycle Engines(LACE Rocket) Posted by annodomini2</DIV> I have and it still boils down to weight and complication. The Shuttle offers a prime example. When the SRB's separate it still needs 130,000 pounds of propellant to reach orbital velocity. Since a Scramjet might be usable to half the altitude of the SRB more rocket propellant would be needed to compensate.To me TSTO works a lot better, it is far less complex and allows an unlimited range of payload capabilities. Two or four SSME's and two permanently mounted SRB's and two turbo-jets. Service it with the Shuttle equipment and mobile launch pads. Payloads and upper stages attach to the side,  jet engines on the manned vehicle would allow escape in an emergency as well as controlled approach and landing and crossrange capabilities.    <div class="Discussion_UserSignature"> </div>

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