#21
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Steam Rockets
Paul Hovnanian P.E. wrote: DougC wrote: tomcat wrote: The liquid hydrogen and lox take up too much room and will, over a period of time, vent into the vacuum of Space. My space ship doesn't have leaks like that. The hydrogen and oxygen can, however, be carried into space as a very dense stable fuel in the form of water. But the water must be vaporized and the water molecules cracked apart into separate hydrogen and oxygen atoms. Toss in a handful of Lithium Aluminum Hydride ( LAH ) How many kg of LAH does it take to split 1 kg of water? Since the weight of the water will be the same regardless of whether its stored as H2 and LOX or water, the only offsetting weight savings will be the elimination of the cryogenics necessary for the former. -- Paul Hovnanian ------------------------------------------------------------------ Just say 'No' to Windows. -- Department of Defenestration. It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. tomcat |
#22
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Steam Rockets
Danny Dot wrote: -- Danny Dot www.mobbinggonemad.org "tomcat" wrote in message oups.com... The idea of using water as a rocket fuel seems extraordinary, but it is feasible for at least part of a rocket's propulsion. Steam vapor is an invisible vapor that has 1600 times the volume of the water it came from. This fact was used to drive steam locomotives. It works. For a rocket, however, the 'trick' is to instantly produce the steam in an explosive kind of way. If possible this will produce considerable thrust. Steam locomotives used a fire box burning coal. To 'instantly' produce steam, however, the old 'fire box' of the steam locomotives is simply too slow. Now you may wonder why you would want to carry water instead of previously separated hydrogen and oxygen. Hydrogen and oxygen are very high volume gases and even as liquids they take up lots and lots of room. It is difficult to to take enough along in specially made cryogenic tanks to be effective. These tanks, moreover, have vents which vent off the gas produced by relatively warm tanks. And this, of course, is waste and reduces the amount of fuel. It makes hydrogen/lox a difficult fuel to use for long missions. Water, on the other hand, is very stable and very dense. It will stay put for very long voyages and can actually be replenished in Outer Space. The Moon, for example, is believed to have more than 600 billion tons of water on it's North and South Poles. Asteroids also have been proven to have water in large quantities. The rings of Saturn and the Poles of Mars are other examples of water in Outer Space. So, the possibility of a 'Steam Rocket' is an exciting one filled with the promise of a stable, dense, and replenishable fuel. The 'trick', however, is to instantly vaporize the water into steam in order to produce enough reaction. The faster the vaporization the greater the ISP and pounds of thrust. Interesting idea. Water on a nuclear core would certainly make a good rocket. This should be possible without contaminating the water. The water could act as a reactor cooling agent while getting zapped with laser, maser, electrode energy generated by the reactor. The cooling of the reactor should put the water on the threshold of cracking. ISP is only a function of the velocity of the gases as they escape the nozzle. Higher temperatures lead to higher velocities, as does lower molecular weight of the exhaust gas. This is why a LOX/H2 rocket has a higher ISP than a kerosene/LOX -- water is a lighter molecule than the combustion products of kerosene/LOX. I believe that ISP is over rated. It is important within the atmosphere because a rocket or plane cannot exceed the speed of it's own thrust. This, however, is NOT true in the vacuum of Outer Space. Today, with rocket thrust becoming an orbital or escape velocity requirement it is thrust to weight that should take priority. When I first became an astronaut instructor in 1990, I was shocked to find out the orbit engines on the shuttle (and most other orbit vehicles) do not use pumps. The roughly 250 psi pressure in the tanks feeds propellant straight into the 125 psi combustion chamber. This keyed my research into ISP and I discovered a small chamber pressure does NOT mean low ISP. I also discovered that ISP in the shuttle computer software is "defined" as VEX, which is the exhaust velocity of the SSMEs. The Russians talk exhaust velocity a lot and use the term ISP less than we do. You are correct that water can be stored in a much smaller tank than hydrogen, but for a heat engine that dumps a liquid onto a heat sorce, the small molecular weight of H2 gives much higher escape velocities for the same temperature. H2 has a molecular weight of 2 and water a weight of 18. At the same temperature H2 will have a HUGE advantange on ISP/VEX. And, I see the max temperature for both would be about the same. This is true when H2 is compared to steam, but we may be capable of reducing water to it's constituent parts: H and O. In such a case the water rocket would have the same ISP as the hydrogen lox rocket. The power would come from the same source, only the fuel injection and combusion chamber design would differ. BUT, having said this, H2 takes HUGE volume to store, can't be stored on orbit, requires major engineering to "handle", requires expensive components to "handle", and is expensive. Maybe water dumped on a nuclear reactor has its place in the world. It could probably get to SSME like ISPs because in both cases the exhaust gases are both water. The question is -- can a nuclear core go to the same temperature of the combusion chamber of an SSME. If the heat engine design could get to the same temperatures, it would be easy to get to SSME ISPs. If the design was orbit only, then higher ISP would be easy because the SSME nozzles are compromized to work at sea level as well as a vaccum. Well, 2500 deg. C. cracks water completely. And, we have materials that can handle that. And, furthermore, we can use regenerative cooling to produce the super heated steam, protecting the combusion chamber and nozzle walls at the same time. tomcat A couple of ideas to produce this instantaneous vaporization is to use a nuclear reactor and/or another rocket using conventional fuels. I believe that either of these two ideas will work. An added bonuis of the 'Steam Rocket' is that at high temperatures -- 1000 deg. C. to 2500 deg. C. -- the water molecule splits. When this molecule comes back together, which it will as soon as the temperature drops, it generates enormous explosive force and roughly 6000 deg. F. temperatures. Basically, at this point, you have a hydrogen-lox combustion with the ISP of the hydrogen/lox engine like the SSME (Space Shuttle Main Engine) for example. Even if a small amount of the water vapor 'cracks' and then comes back together as a hydrogen lox reaction it would add enormous explosive reaction to the Steam Rocket and should make it a practical rocket for use in Outer Space. tomcat |
#23
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Steam Rockets
Henry Spencer wrote: In article , Danny Dot wrote: ISP is only a function of the velocity of the gases as they escape the nozzle. Higher temperatures lead to higher velocities, as does lower molecular weight of the exhaust gas. This is why a LOX/H2 rocket has a higher ISP than a kerosene/LOX -- water is a lighter molecule than the combustion products of kerosene/LOX. Actually, the real story there is more complex and somewhat different -- even though many textbooks claim the above -- because temperature and molecular weight are not independent in a chemical rocket. (John Clark's "Ignition!" is one of the few references that gets the story right, probably because Clark was a propellant chemist rather than a rocket engineer, and had to understand the underlying details.) The correlation between lighter molecules and higher velocity is due to indirect effects. For a nuclear rocket, though, the situation is much simpler, because there temperature *is* independent of propellant. There, molecular weight matters directly and strongly. Let's not be purists. Turn some of that reactor energy into electrical juice and zap the propellent with a hefty dose of laser, maser, and sheer electricity at the same time it is cooking in the hot tube. You could inject a little lithium aluminum hydride at the same time if you want to. When I first became an astronaut instructor in 1990, I was shocked to find out the orbit engines on the shuttle (and most other orbit vehicles) do not use pumps... This keyed my research into ISP and I discovered a small chamber pressure does NOT mean low ISP. Correct. To a first approximation, Isp is independent of pressure. Higher chamber pressure pushes more gas through per second, but it's the thermal energy of combustion that determines Isp, and that's not (very) dependent on pressure. The RL10 has slightly higher Isp than the SSME despite a much lower chamber pressure. Where it really gets counterintuitive is with cold-gas thrusters on spacecraft. The gas is typically stored at very high pressure... but it goes through a pressure reducer/regulator before reaching the thrusters! This boggles novices' minds. The reduction doesn't matter, because it's the thermal energy of the gas that drives the expansion through the nozzle, *not* the feed pressure. I also discovered that ISP in the shuttle computer software is "defined" as VEX, which is the exhaust velocity of the SSMEs. The Russians talk exhaust velocity a lot and use the term ISP less than we do. The Europeans confuse the matter further by using velocity units (rather, a mixed-up version of velocity units -- N-s/kg) and calling it Isp. It's exhaust velocity that really matters, but Isp is more convenient for comparisons, not least because it extends gracefully to airbreathing engines, where exhaust velocity does not tell the full story. Isp is a better choice as a figure of merit, even though it needs to be converted to turn it into something physically meaningful. In the vacuum of Space it is thrust-to-weight that counts. And, in the weightlessness of Interplanetary Space it is continuous power that wins the contest, such as an ion engine. BUT, having said this, H2 takes HUGE volume to store, can't be stored on orbit, requires major engineering to "handle", requires expensive components to "handle", and is expensive. Maybe water dumped on a nuclear reactor has its place in the world. A better choice is ammonia -- almost as easy to store as water, comes apart easily and completely into nitrogen and hydrogen when you get it hot, and *doesn't* recombine. The resulting average molecular weight is about 8.5, giving a nuclear-rocket Isp about half that of hydrogen. Water doesn't break down significantly at any reasonable reactor temperature, so its molecular weight stays at 18, giving about 1/3 of the hydrogen Isp. (Worse, it's an oxidizing agent when you get it hot, which is hard on the usual reactor materials.) It could probably get to SSME like ISPs because in both cases the exhaust gases are both water. The question is -- can a nuclear core go to the same temperature of the combusion chamber of an SSME. No, not even close. The core of an orthodox solid-core nuclear rocket is limited, by materials issues, to considerably lower temperatures than that of a high-pressure oxygen/hydrogen flame. (The nuclear core has to run hotter than the gas, whereas the chamber walls of a chemical rocket can run much cooler.) Using both the reactor's heat and it's electrical output should solve the problem. As stated above, the combination of heat with laser, maser, electricity should 'cook off' the water right when it hits the combustion chamber. Since steam is involved as well as the 'cooking' process a 'Steam Rocket' might do best with a double combustion chamber. You could think of it as adding an afterburner. The first chamber cooks, separates, and pushes super heated and super expanded steam into the second chamber where regenerative cooling makes it a bit cooler than the previous putting the hydrogen and oxygen back together. The should yield a big second "Bang". tomcat |
#24
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Steam Rockets
On Sat, 05 Aug 2006 08:43:44 -0500, in a place far, far away, Wilbur
Slice made the phosphor on my monitor glow in such a way as to indicate that: I am considering the possibility of using the F-1 kerosine and lox engine along with the steam rocket engine. That way the excess heat of the F-1 engine can be used to produce super heated steam which, in turn, can be zapped with electricity, microwaves, or lasers to crack the water molecules. The other possibility is to use a nuclear reactor, a small one mind you, that can produce hundreds of kw for the electrodes, masers, or lasers. There may be yet other alternatives. I solicit ideas, suggestions, and wayward thoughts on the subject. Here's a suggestion. Go learn some mathematics, and physics. |
#25
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Steam Rockets
"tomcat" wrote in message
ups.com I believe that ISP is over rated. It is important within the atmosphere because a rocket or plane cannot exceed the speed of it's own thrust. This, however, is NOT true in the vacuum of Outer Space. Today, with rocket thrust becoming an orbital or escape velocity requirement it is thrust to weight that should take priority. Well, 2500 deg. C. cracks water completely. And, we have materials that can handle that. And, furthermore, we can use regenerative cooling to produce the super heated steam, protecting the combusion chamber and nozzle walls at the same time. However, within a near absolute vacuum of 1e-18 bar it shouldn't require 2500 deg. C., or does it? I otherwise totally agree, so please do bother to tell that one to those smart Third Reich folks encharge of their nearly 30% inert GLOW massive Saturn-V rocket that somehow still managed at nearly a 60:1 ratio of rocket/payload in getting such a horrific amount of their Apollo payload tonnage and of so quickly into orbiting our moon. Outside of your NASA koran, got any modern and otherwise proven rocket-science that'll back any of that hocus-pocus up? Why do you keep excluding the superior energy density worth of h2o2/c3h4o LRBs, much like water that'll keep rather nicely without either being sub-frozen and thus requiring such a great deal of insulation and many other technological complications? 98% h2o2 at 1.4 g/cm3 is just plain old water on steroids that can be ignited as is. Perhaps better yet, isn't there such things h2o3 or h2o4? BTW; what extra tonnage of ice loading did those Saturn-V rockets have to deal with? - Brad Guth -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#26
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Steam Rockets
tomcat wrote:
Paul Hovnanian P.E. wrote: DougC wrote: tomcat wrote: The liquid hydrogen and lox take up too much room and will, over a period of time, vent into the vacuum of Space. My space ship doesn't have leaks like that. The hydrogen and oxygen can, however, be carried into space as a very dense stable fuel in the form of water. But the water must be vaporized and the water molecules cracked apart into separate hydrogen and oxygen atoms. Toss in a handful of Lithium Aluminum Hydride ( LAH ) How many kg of LAH does it take to split 1 kg of water? Since the weight of the water will be the same regardless of whether its stored as H2 and LOX or water, the only offsetting weight savings will be the elimination of the cryogenics necessary for the former. It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. OK, how many cm^3 of LOH does it take to split 1 cm^3 of water? -- Paul Hovnanian ------------------------------------------------------------------ "There's something vewy scwewy going on awound here." -- Elmer Fudd |
#27
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Steam Rockets
tomcat wrote:
[snip] It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. Are you planning on using this engine for propulsion during the waverider's flight? If so, leave the oxygen (or most of it) behind and use an air breathing engine. You only need the O2 above the atmosphere. If you are using the waverider for re-entry (like the space shuttle) and launching with a rocket, then its weight that matters. Particularly if you can use a multi-stage vehicle, volume isn't nearly as important as weight. -- Paul Hovnanian ------------------------------------------------------------------ Opinions stated herein are the sole property of the author. Standard disclaimers apply. Celebrity voice impersonated. Batteries not included. Limit one to a customer. Best if used by April 1, 2007. Refrigerate after opening. Void if removed. |
#28
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Steam Rockets
Paul Hovnanian P.E. wrote: tomcat wrote: [snip] It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. Are you planning on using this engine for propulsion during the waverider's flight? If so, leave the oxygen (or most of it) behind and use an air breathing engine. You only need the O2 above the atmosphere. If you are using the waverider for re-entry (like the space shuttle) and launching with a rocket, then its weight that matters. Particularly if you can use a multi-stage vehicle, volume isn't nearly as important as weight. -- Paul Hovnanian ------------------------------------------------------------------ Opinions stated herein are the sole property of the author. Standard disclaimers apply. Celebrity voice impersonated. Batteries not included. Limit one to a customer. Best if used by April 1, 2007. Refrigerate after opening. Void if removed. Waveriders have to be aerodynamic. If they are too big then they are apt to have too much drag. In short, they are 'flying gas cans' that have to be shaped for hypersonic speeds within the atmosphere. Waveriders, on the other hand, use air pressure underneath the vehicle to hold the weight. They can be heavier per thrust amount than can a vertical rise rocket. tomcat |
#29
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Steam Rockets
tomcat wrote:
Paul Hovnanian P.E. wrote: tomcat wrote: [snip] It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. Are you planning on using this engine for propulsion during the waverider's flight? If so, leave the oxygen (or most of it) behind and use an air breathing engine. You only need the O2 above the atmosphere. If you are using the waverider for re-entry (like the space shuttle) and launching with a rocket, then its weight that matters. Particularly if you can use a multi-stage vehicle, volume isn't nearly as important as weight. -- Paul Hovnanian ------------------------------------------------------------------ Opinions stated herein are the sole property of the author. Standard disclaimers apply. Celebrity voice impersonated. Batteries not included. Limit one to a customer. Best if used by April 1, 2007. Refrigerate after opening. Void if removed. Waveriders have to be aerodynamic. If they are too big then they are apt to have too much drag. In short, they are 'flying gas cans' that have to be shaped for hypersonic speeds within the atmosphere. Waveriders, on the other hand, use air pressure underneath the vehicle to hold the weight. They can be heavier per thrust amount than can a vertical rise rocket. The only application I've heard so far for a waverider space vehicle is for the re-entry phase. Going up isn't a problem of aerodynamics. You just strap on big fuel tanks and kick them loose at the end of the boost phase. To date, I'm unaware of any efficient way to go orbital from aerodynamic flight with any significant payloads. -- Paul Hovnanian ------------------------------------------------------------------ c (velocity of light in a vacuum) = 1.8x10^12 furlongs per fortnight |
#30
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Steam Rockets
Paul Hovnanian P.E. wrote: tomcat wrote: Paul Hovnanian P.E. wrote: tomcat wrote: [snip] It is the savings in 'Volume', not weight, that is so important. You can only make a waverider so big. Are you planning on using this engine for propulsion during the waverider's flight? If so, leave the oxygen (or most of it) behind and use an air breathing engine. You only need the O2 above the atmosphere. If you are using the waverider for re-entry (like the space shuttle) and launching with a rocket, then its weight that matters. Particularly if you can use a multi-stage vehicle, volume isn't nearly as important as weight. -- Paul Hovnanian ------------------------------------------------------------------ Opinions stated herein are the sole property of the author. Standard disclaimers apply. Celebrity voice impersonated. Batteries not included. Limit one to a customer. Best if used by April 1, 2007. Refrigerate after opening. Void if removed. Waveriders have to be aerodynamic. If they are too big then they are apt to have too much drag. In short, they are 'flying gas cans' that have to be shaped for hypersonic speeds within the atmosphere. Waveriders, on the other hand, use air pressure underneath the vehicle to hold the weight. They can be heavier per thrust amount than can a vertical rise rocket. The only application I've heard so far for a waverider space vehicle is for the re-entry phase. Going up isn't a problem of aerodynamics. You just strap on big fuel tanks and kick them loose at the end of the boost phase. To date, I'm unaware of any efficient way to go orbital from aerodynamic flight with any significant payloads. -- Paul Hovnanian ------------------------------------------------------------------ c (velocity of light in a vacuum) = 1.8x10^12 furlongs per fortnight "To date, I'm unaware of any efficient way to go orbital from aerodynamic flight with any significant payloads." -- Paul Hovnanian Just because it hasn't been done doesn't mean that it can't. Technology has reached the point where waveriders, completely reusuable rocketry, can be built and reach orbit. They must, however, carry 10 times their thrust weight in combined dry weight and fuel (GLOW). It will take roughly 1 hour to reach orbit. The SSME has proven capable of long burn times. The SSME has the 'punch' to do the job. This may also be the case of the J-1a though the burn time might exceed it's capability. The J-1a is a kerosone and lox rocket that would reduce waverider size somewhat. The SSME (Space Shuttle Main Engine) packs 400 thousand pounds of thrust at sea level, while consuming 1035 pounds of fuel per second. The J-1a packs 1.8 million pounds of thrust at sea level, while consuming 6000 pounds of fuel per second. The day of the waverider has arrived. One just needs to be built. tomcat |
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