#141
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fun with expendable SSTOs (was The 100/10/1 Rule.)
In article ,
Rand Simberg wrote: Unfortunately, I'm not going to make Space Access this year, to my great annoyance, so the talk won't appear. Deadline problems. We'll be sorry to miss you, Henry. Is this unprecedented? Yep, first time I've missed one, and I'm sorry about it too. I really thought I could make it -- had hotel and plane reservations -- but I've been ill lately (nothing dire but it's really slowed me down), and a big hard deadline is coming up. In theory I could attend and still make the deadline... if nothing goes wrong... but my colleagues on this project have been very patient with me, and I owe it to them to leave a reasonable safety margin, and it just wasn't there. Rats. And I think you're wasting your time with Craig. He's got the true religion. Once in a while I'll sally forth against the heathens :-) just to make sure that their claims don't go unchallenged in public. A few of the worst cases I just don't bother with any more, in the interests of my blood pressure :-), but Craig hasn't reached that point, yet. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#142
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fun with expendable SSTOs (was The 100/10/1 Rule.)
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#143
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fun with expendable SSTOs (was The 100/10/1 Rule.)
In article ,
john hare wrote: If I ever get started again, I have business reasons for a continuing interest in some airbreathing cruise. If my business model matches reality closely enough, The mass penalties will be acceptable. If I get money, it will most likely come from pilot/businessmen. If we ever fly, it will probably have to be from airports that have not done the paperwork to become spaceports. If you have reason for wanting a period of low-speed cruise after takeoff or before landing, *then* airbreathing can make considerable sense, since cruise (as opposed to acceleration) is something rockets are not good at. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#144
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fun with expendable SSTOs (was The 100/10/1 Rule.)
John Schilling wrote: Propane may be slightly better as a launcher fuel, but it's a cryogen (albiet a soft one), which makes it much worse as a missile fuel. As most everyone who has ever built a space launch vehicle has also been in the missile-building business as well, they've understandably gone and standardized on kerosene as their hydrocarbon fuel of choice. How about butane? It stays liquid at ambient temperature at far lower pressures than propane. Refill butane for lighters comes in pressure vessels not much thicker-skinned than beer cans. Pat |
#145
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fun with expendable SSTOs (was The 100/10/1 Rule.)
In article ,
Pat Flannery wrote: Propane may be slightly better as a launcher fuel, but it's a cryogen (albiet a soft one), which makes it much worse as a missile fuel... How about butane? It stays liquid at ambient temperature at far lower pressures than propane. Pure butane in fact has a vapor pressure of about 31psi, which is perhaps a bit higher than you'd like but not too bad. However, at room temperature it may not have much of an advantage over kerosene, which is certainly easier yet to handle. And unlike propane, it doesn't stay liquid at LOX temperatures, a property that has some appeal. (Note that, as John said, for *launchers*, the fact that propane is a soft cryogen is not a significant problem.) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#146
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fun with expendable SSTOs (was The 100/10/1 Rule.)
On Mar 19, 12:12�am, Pat Flannery wrote:
John Schilling wrote: Propane may be slightly better as a launcher fuel, but it's a cryogen (albiet a soft one), which makes it much worse as a missile fuel. *As most everyone who has ever built a space launch vehicle has also been in the missile-building business as well, they've understandably gone and standardized on kerosene as their hydrocarbon fuel of choice. How about butane? It stays liquid at ambient temperature at far lower pressures than propane. Refill butane for lighters comes in pressure vessels not much thicker-skinned than beer cans. Pat |
#147
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fun with expendable SSTOs (was The 100/10/1 Rule.)
Yeah, water might be acceptable, but adding energy too is probably better.
From your posting, you still don't get it yet. Extrapolating results of studies between this and than to a third thing can lead to false conclusions. It's dangerous to extrapolate outside the useful range of some trade study and the thumb rule may not apply. Is it the Hydrogen or the fact that the Saturn V tank must support the payload above, big tank supporting big payload weighs more than small tank supporting big payload. Better take that into account, OK, don't support any weight with the big tank. Well, that's good for exo-atmospheric SSTOs with rockets, they don't have any payload, problem solved. Reaction time, Hydrogen shines here too. Time in nozzle, you didn't notice I said plug somewhere in there. A plug after the throat keeps the flow in the nozzle at a much slower supersonic speed. Therefore, just past the throat the jerk isn't so large. The Mach number and pressure where the bypass (not so high pressure) hydrogen or oxygen is added is also chosen. The flow is manipulated to keep it slow, giving more reaction time. Pipe, the pipe is just to deliver the not so high pressure liquids past the throat. The input end is very near the turbines too, nice. The Christmas Tree attached to the pipe is non-trivial, hence all the fun Trade Studies to figure out the how to do it right. A Trade Study of how to optimize it, with lots of variable. I've been giving you and everybody else hints the whole time. Hydrogen, so much energy in such a small package? Hydrogen, 1, fuel Oxygen, 16, oxidizer Carbon, 12, dense liquid fuel Aluminum, 27, even more dense typical solid type fuel Iron, 56, and even more dense Opportunity missed, yeah I started talking about dumping in denser fuels then switched over to lighter fuels. Even hit return before noticing (a little bit later) I forgot to switch the rich mixtures. Which rich mixture is exiting the throat. Surprise, no I it didn't just discover that the rich mixtures should have been switch. Fixed the backflow, but not the Thrust, instead of fixing both. You could have simply done that too, opportunity missed. Hard to beat a Mixture Ratio range of 16 for Hydrogen and Oxygen. Allowing for widest variation along the Thrust/ISP curve. High Thrust/Low ISP on the Oxygen side, Low Thrust/High ISP on the Hydrogen side. Just what an SSTO needs, High Thrust Early with ISP continously climbing as best it can, all the way to the Space Station. Oxygen/Carbon is only 1.33, Iron/Oxygen 3.5. Not even close to the potential of Oxygen/Hydrogen. So much energy at the optimal mixture ratio it's just too hot to burn completely. Premixed, half burnt, Oxygen/Hydrogen exiting the throat, some of it combining in the nozzle and some wasted, exiting the nozzle unburnt. Yeah, so adding water isn't that bad an idea to make sure all the Hydrogen and Oxygen are also water before exiting the nozzle. Water, 18, propellent Argon, 40, heavier propellent Xenon, 131, even heavier propellent Wow, exhaust propellent mass ratio range of 7.2 Xenon/Water. Hello ... Air Liquide ... Hi, how are you today ... Yes, I'd like to order a half million gallons of Xenon per month, and could you give me a price on that ... Ahhh ... Ahhh ... Ahhh, better make that Argon(2.2) ... Hold on, let me think about it ... Nitrogen(1.5) ... Oxygen(1.78) ... Carbon Dioxide(2.44) ... Ahhh, yes that will do, and how much are the delivery charges to Mars ... What? ... Ahhh, thanks for your help but, I think I'll just liquefy my own when I get there. HOTOL???, How not to fly in the Atmosphere to Orbit, yeah, yeah, I agree. This and that, negative outcome, yep. Only reason to build HOTOL is to do it, gain experience, fine tune models, spark imagination, research platform, improve the state of the art, find the next step, walk a little further. Just studying it just isn't quite the same. I still think it's better to take some payload with an SSTO in the Atmosphere. ;-) -- Craig Fink Courtesy E-Mail Welcome @ -- Henry Spencer wrote: In article nk.net, Craig Fink wrote: What should the mass be? Well, since the engine is already running on the extreme Oxygen rich side, probably any old heavy dense liquid that reacts well with Oxygen would do. Since pressures are lower in the bell, maybe even a pressure fed tank might work... If you're injecting into the supersonic flow, you might as well just use water. There won't be *time* for any significant reaction; the exhaust is moving *fast* at that point, and accelerating fiercely, and it just doesn't stay in the nozzle for long. The usual rule of thumb is that reaction rates even in the already-mixed combustion gases are effectively zero after the throat. Even just reasonable mixing -- which is what's needed if you want to bulk out the exhaust this way -- is doubtful with just a straight pipe. You need some kind of atomization, even if it's only plugging the end of the pipe and drilling a bunch of holes in its side just above the end. Some kind of non-trivial injector discharging into the chamber will work a lot better. At which point, of course, you can start thinking about how much hydrogen and how much dense fuel is appropriate. Interestingly enough, you might find that the percentage of hydrogen keeps going down as you analyze more carefully. Surprise, you've just discovered that dense fuels are better for SSTOs than hydrogen... I still think Atmospheric Flight to Orbit is the way to go, I kind of like the extra payload to Orbit. Odd that people who actually study this in detail quite consistently find that it gives less payload to orbit. (E.g., the HOTOL team found that going all-rocket, with other assumptions left unchanged, would more than double their payload. Same story as dense fuels vs. hydrogen: lower Isp, but also much lighter hardware bringing the mass ratio way up.) |
#148
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fun with expendable SSTOs (was The 100/10/1 Rule.)
john hare wrote:
"Henry Spencer" wrote in message ... In article . net, Craig Fink wrote: ...I bring up "Fluid Variable Intakes" which fits nicely with his engine and invalidating certain assumptions of his trade study. His study just swung in a different direction. I don't believe you explained what "Fluid Variable Intakes" are. *It's not a term I'm familiar with either, although I don't keep up with the current fads :-) on the airbreathing side. I don't keep up with the fads to much either. To be honest, I just made the term up. I thought it best described what it was, a "Fluid Variable Intake", sounds good to me. If it's not really a physical cooler (cooling really just a bonus) and not really a physical inlet, and it's variable, what is it? The concept, I made that up too. It also sounded good to me, it would essentially let a slightly modified jet aircraft fly straight up exit the atmosphere at Mach 5, winning the X-Prize. But, like I said, it's hard to find a good used engine/supersonic "non-government developed" aircraft these days. If you have a better name, or know of a different name that it goes by, let me know. It would be fun reading about it. It would have needed negative mass to counteract the engine weight to a degree necessary to match pure rocket stage performance. I lost interest somewhat in supersonic intakes when it became clear that there could not be a cost advantage to them. Someone's selling tickets for short zero gee trips in a modified commercial airliner for probably $1000, someone else is selling tickets in supersonic aircraft for $10,000-$20,000, and someone else will soon be selling long zero gee trips in custom designed rocket planes for $200,000. There is a whole lot of room between $1000-$20,000 and $200,000 to sell tickets for long zero gee trips in turbojet/rocket powered aircraft. |
#149
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Fluid Variable Intakes ( fun with expendable SSTOs ...)
Fluid Variable Intakes
For Acceleration type mission profiles with Turbojet, Ramjet, and Scramjet. Fluid Variable Intakes fix many of the difficult problems associated with these engines, making it possible to use a single fixed inlets or a much less complex inlet. As the aircraft passes the maximum design Mach Number for the inlet, a fluid is used to compensate for the changing area ratio between the beginning of the inlet and the sonic throat. Cryogenic Oxygen / Gaseous Oxygen being the fluid, also enriches the air taken in by the engine with Oxygen, enhancing the performance when it is needed to continue to accelerating. It reduces the complexity of the associated inlet hardware, replace complex mechanical moving aerodynamic surfaces with a fluid distribution system. It's also possible to preheat the Cryogenic Oxygen to gasify it at a relatively high pressure to dynamically bring throat to sonic conditions, reducing the Oxygen flow rate. This allows the Oxygen flow rate to be regulated to maintain engine operating conditions, statically added mass (dumping) vs dynamically added mass (thrusting) Oxygen in the inlet. It cools the air, radically reducing compressor inlet temperatures. Since Oxygen flow rate is related to Mach number, performance is maintained as the aircraft continues to climb and accelerate. Essentially, it slowly converts the engine from an airbreather into a rocket smoothly varying the performance during acceleration from an Specific Fuel Consumption (ISP in rocket terms) greater than 2000 down to something less than 500 at the end of the acceleration. Normally for turbojets the added Oxygen would be a problem for turbine inlet temperatures. But this can be compensated for by changing the mixture ratio in the combustion chamber. Switching from a fuel lean mixture ratio combustion usually used for endurance/range type missions, to a fuel rich mixture. Essentially going over the high temperature hump, to an extremely fuel rich condition. This also adds mass flow through the turbine, spinning the compressor and turbine up. The fuel rich turbine exhaust can then be mixed with the bypass air as an afterburner. The bypass air also enriched with Oxygen. Hydrogen, with double the energy per weight of any other fuel would probably be the best fuel for such an acceleration type mission. It also would simplify combustion, ensuring complete combustion. Fluid Variable Intakes smoothly transition an airbreathing engine into a rocket engine and allows an aircraft continue accelerating quite a bit past what would normally be considered it's maximum speed. Probably not very useful for endurance/range type mission, but extremely useful for acceleration type mission, and going to Orbit in the Atmosphere. -- Craig Fink Courtesy E-Mail Welcome @ -- Henry Spencer wrote: I don't believe you explained what "Fluid Variable Intakes" are. *It's not a term I'm familiar with either, |
#150
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Fluid Variable Intakes ( fun with expendable SSTOs ...)
Hi Derek,
I have a choice, how to respond to your post. The response can be negative or positive. Which shall it be. Hummm, lets go with positive. From my point of view: ;-) Interesting how in these threads, Henry invokes religion as an argument for non-Atmospheric Flight to Orbit. The connotation of "religion" negative and with a negative rate of change right now. Then another, and another, till the choirs joins in. You should really check before chiming in about God and another Man's religious belief. If you must know, I'm Christian, of the variety that believes Physics is simply Man's description of God's work. Math being the language that it's spoken in. To understand Physics is to understand God's work, and therefore it is the duty of Man to try the best he can to relieve himself of his own ignorance. Ignorance, also has a bad connotation, when it really shouldn't. For we are all born ignorant, not knowing, and begin our own personal journey to relieve ourselves of our own ignorance. No one can do this for us. If there is something you don't understand (ignorance) about the concept of Fluid Variable Intakes, just ask. Your more likely to get a response if you ask nicely, positive than negative. Jeff Findley, is just making comments about one example of an application of Fluid Variable Intakes, not all applications. His comments are for the most part true. In an application with compressors and turbines, a complicated device that required a large effort to perfect, it's most likely true. Is it more, or less. I don't know. His comments about the lack of papers is most likely true, as Henry and John have both made similar comments. But, not surprising, all new concepts start out this way. Maybe Jeff, if he has the knowledge and background, might write one of the dozens of AIAA papers to come. That is, if it truely is a good concept/technique. Looking at a much simpler application that would require much less work than incorporating it with compressors and turbines would be a ramjet. A much simpler engine, pure fluid manipulation, just adding a little bit more fluid manipulation. Anywhere from trivial to massive, depending on the approach and who's doing it. Surely you've clicked and gone here by now http://www.grc.nasa.gov/WWW/BGH/shorth.html here, http://exploration.grc.nasa.gov/educ...et/shortr.html and here, http://www.grc.nasa.gov/WWW/K-12/airplane/shortp.html Looking for Ramjets, problems with, and when the region of usefulness ends and why. Ah, here; http://www.grc.nasa.gov/WWW/K-12/airplane/lowhyper.html .... For aircraft speeds which are much greater than the speed of sound, the aircraft is said to be hypersonic. Typical speeds for hypersonic aircraft are greater than 3000 mph and Mach number M greater than five, M 5. We are going to define a high hypersonic regime at M 10 to account for re-entry aerodynamics. The chief characteristic of hypersonic aerodynamics is that the temperature of the flow is so great that the chemistry of the diatomic molecules of the air must be considered. At low hypersonic speeds, the molecular bonds vibrate, which changes the magnitude of the forces generated by the air on the aircraft. At high hypersonic speeds, the molecules break apart ... Because of the pressure losses associated with the terminal shock of the inlet, a ramjet has very limited performance beyond Mach 5 ... High temperatures, vibrating bonds of diatomic molecules breaking apart. Ramjets are limited to Mach 5. So this is the point where the first ounce of LOX needs to be added, to go past Mach 5 with a ramjet. Super-cold liquid Oxygen, a huge heat sink, better use it wisely and add just enough to keep the vibrating bonds from vibrating too much or breaking apart. Add a little more Mdot (Mass flow rate) at Mach 6, even more Mdot at Mach 7, quite a bit more at Mach 10, all to keep vibrating bonds of diatomic molecules from vibrating too much and/or breaking apart. Extending the useful range of a simple ramjet well past Mach 5 and probably past Mach 10. Just how far? Sounds like a fun Trade Study. Acceleration mission requirements are significantly different than Range/Endurance mission requirements, which can lead to a significantly different solution. Almost all in the atmospheric hypersonic flight studies and research has been for Range/Endurance mission type profile. Even the X-43A hypersonic research aircraft, they were very proud to have used only fuel. Adding the Oxidizer into the equations adds a whole new dimension that is well suited for the Acceleration mission profile for many many reasons, making Atmospheric Flight to Orbit not only possible, but with superior performance over exo-Atmospheric Ascent. The fun part to me, is the challenge of how to fit all the pieces of the puzzle to do this. -- Craig Fink Courtesy E-Mail Welcome @ -- Derek Lyons wrote: "Jeff Findley" wrote: This isn't the sort of thing you can do with out *a lot* of detailed aerodynamic, combustion, and thermal analysis. Not to mention how much wind tunnel time this sort of research would consume. This is the sort of thing that can easily burn a billion dollars worth of research grants and never fly real hardware. Remember NASP? Yes, I remember NASP. I worked on the NASP program and developed a closed loop first stage guidance for the Space Shuttle. Really neat algorithm :-) What a closed loop first stage guidance for the Space Shuttle and NASP have in common, ????, your going to have to ask a manager about the convoluted logic. I was young, and really just happy to have the opportunity to develop it. The algorithm I named BIG, which used a small (2 pages of code) 3-dof trajectory simulation called SIMP, written by a coworker. And NASP was easier than an accelerator since it would have been optimized for supersonic cruise. Not only that, but it takes the sole 'advantage' of an airbreather (that one need not pack along the excess mass of oxidizer) - and tosses it into the crapper. So, where's the papers? Certainly someone who's done the work has produced a few dozen AIAA papers, right? I'm sure we'd all be interested in the detailed analysis. Until then, liquid fueled rocket engines are the preferred off the shelf solution to getting to orbit. Such a stunning triumph of religious fervor needs not such mundane things as actual proof. D. |
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