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Why is a LOX/Kero SSTO not rather easy?
I am not a particular fan of SSTO, but it appears to me that SSTO has long been within our grasp. The best figures that I could get for the Titan II 1st stage (based on Rusty Barton's reply to my earlier post) are a GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of 23.7. Now comparing it to a LOX/kero vehicle powered by something like the Russian NK-33, I see the following plus and minus factors affecting its mass ratio (I am not including a payload in these calculations): On the minus side, the Titan II 1st stage is not a complete vehicle. It: (a) lacks a nose cone (b) lacks most avionics (c) lacks a cargo bay (d) has 6% denser fueland so has a slightly smaller fuel tank On the plus side: (a) the NK-33 is 420 lbs lighter than the Titan II engine yet it is sufficient for a vehicle nearly 10% heavier (b) the structure does not have to support the 32 ton 2nd stage and so can be significantly lighter. My guess is that those factors mostly cancel out. I also assume that making a vehicle reusable adds about 40% to its dry weight: Wings add 7% Landing gear add 3% TPS add 15% Other add 15% So if we crank those factors in: Dry weight = 10900*1.4 = 15300 lbs Glow = 258000 + (15300 - 10900) = 262400 MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15 Now for the NK-33 we have an average Isp of 331, and given a required dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air resistance, lower back pressure losses, and earlier peak acceleration) we get a required MR of 17.01, which is slightly less than what we can achieve. So we can make orbit with a single stage using very old technology. Of course, this is without payload, but given the fact that the Titan II 1st stage was not optimized for weight (you would not normally optimize a 1st stage) and we have lighter materials today, such as aluminum-lithium and carbon fiber, I would think we would have the necessary margin for a significant payload. We also might fly with a wet wing and eliminate the kerosene tank altogether. And of course if we scaled it up by a factor of 3 we would gain a substantial economy of scale. So it appears to me that we have had reusable SSTO capability for dense fuel vehicles for a long time. -- Larry |
#2
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Why is a LOX/Kero SSTO not rather easy?
Larry Gales wrote in message news:Pine.WNT.4.56.0308302326280.2728@homecomps. ..
I am not a particular fan of SSTO, but it appears to me that SSTO has long been within our grasp. The best figures that I could get for the Titan II 1st stage (based on Rusty Barton's reply to my earlier post) are a GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of 23.7. Now comparing it to a LOX/kero vehicle powered by something like the Russian NK-33, I see the following plus and minus factors affecting its mass ratio (I am not including a payload in these calculations): On the minus side, the Titan II 1st stage is not a complete vehicle. It: (a) lacks a nose cone (b) lacks most avionics (c) lacks a cargo bay (d) has 6% denser fueland so has a slightly smaller fuel tank On the plus side: (a) the NK-33 is 420 lbs lighter than the Titan II engine yet it is sufficient for a vehicle nearly 10% heavier (b) the structure does not have to support the 32 ton 2nd stage and so can be significantly lighter. My guess is that those factors mostly cancel out. I also assume that making a vehicle reusable adds about 40% to its dry weight: Wings add 7% Landing gear add 3% TPS add 15% Other add 15% So if we crank those factors in: Dry weight = 10900*1.4 = 15300 lbs Glow = 258000 + (15300 - 10900) = 262400 MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15 Now for the NK-33 we have an average Isp of 331, and given a required dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air resistance, lower back pressure losses, and earlier peak acceleration) we get a required MR of 17.01, which is slightly less than what we can achieve. So we can make orbit with a single stage using very old technology. Of course, this is without payload, but given the fact that the Titan II 1st stage was not optimized for weight (you would not normally optimize a 1st stage) and we have lighter materials today, such as aluminum-lithium and carbon fiber, I would think we would have the necessary margin for a significant payload. We also might fly with a wet wing and eliminate the kerosene tank altogether. And of course if we scaled it up by a factor of 3 we would gain a substantial economy of scale. So it appears to me that we have had reusable SSTO capability for dense fuel vehicles for a long time. -- Larry We had a similar discussion here under "Low mass ratio SSTO" . I think people just want to write papers and justify large RD budgets that end up being spent on people who do not work. They need big ticket buzzwords like SSTO or fusion reactors. They just take the money, promise something that's hard to do like a non cylindrical fuel tank or a SCRAM jet engine and later they just say, oh well we did not succeed. Of course many times they do not need to say a thing because they get lucky and the project is cancelled before they are supposed to deliver hardware. Of course it is easy to build SSTO. Zoltan |
#3
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Why is a LOX/Kero SSTO not rather easy?
A LOX/Kero SSTO would be fairly straightforward (I
hesitate to say easy only because any major project, even just digging a big ditch (like the Suez canal) has its own difficulties and complexities). I perceive several reasons why such things aren't being built now. First, is history. From the beginning, orbital rocketry was pretty difficult. The engines available were terrible, and were it not for the fact that liquified gasses and the means to handle them in bulk had been developed since well before the turn of the 20th century it might have been even worse. More so, building very strong structures which are also very light is, and has been, a substantial challenge. If it were not that the aircraft industry had been working in the same direction about a step ahead of rocketry in the early days (since large scale aircraft preceded large scale rocketry by only a few decades), it would certainly have been much, much worse. Anywho, what all that meant (poor engines, and clunky structures, even when both were state of the art) was that SSTO was impossible early on. The early liquid fueled rockets had Isps about as high as the best solid rockets do today. And especially in that Isp range with respect to orbital rocketry any significant performance hit bites pretty hard (an Isp of ~240s leads to a mass fraction to reach orbital speed of *twice* that as with an Isp of ~300s (which is the lower end of the range of Isps for current Kero engines)). Factor in the unfamiliarity both with building very large rockets (e.g. Saturn V class, since you get a hefty advantage in dry mass fraction as you scale up) and with building very low dry mass fraction rockets and that led to the result that staged rockets were the only way to get to orbit. At the time. Here's where the second point comes in, since rocketry was so difficult early on and seemingly so fickle that a kind of institutionilzed cult of accumulated superstition arose. More like the shipwrights of old than, say, the cpu designers of today, rocket builders were enormously leery of from-scratch designs and instead opted for evolving, modifying, and scaling old designs to get what they wanted. And that led to a whole host of ideas becoming fixed in the head of the industrial and government aerospace establishment, including things like LOX/LH2 being a superior fuel than denser fuels, a fixation on minimizing GLOW in relation to payload size, etc. As the rocket industry developed, rather than getting rid of old preconceptions, mostly they just added new ones (such as the "inherent" advantages of winged RLVs over capsules). That inertia has morphed itself into the hand-built, multi-stage launch vehicles you see today and into the idea that SSTO is a really difficult problem. Third and finally, and this is the important point, the launch vehicle business is already established and current launch vehicles meet the needs of the customers fairly well. Brand new vehicles, especially of different designs, would have to develop rather quickly and mold themselves (at leas initially) more to the common characteristics of current launch vehicles (especially in terms of g-loading and vibration). And that adds a development burden to anyone wanting to do an SSTO that would be commercially viable with existing markets. Though there are emerging markets which may provide useful niches. One of the biggest problems of SSTOs is that they have too much thrust. When you take a single stage with only a small payload and you take the engines which are designed to lift it off the ground by brute force with fuel tanks to the brim and you keep those same engines on when the fuel tanks are empty (i.e. when the vehicle plus payload weighs at most 1/7th as much (for the best LOX/LH2 engines) or more likely less than 7% as much (for really good LOX/Kero engines)), you end up with a hell of a lot of excess gees. In fact, for a manned LOX/Kero SSTO, if the engines weren't throttled down the g-load at engine burnout would be pretty close to lethal. High g-loads are slightly more tolerable but not all that much better for multi-million dollar pieces of machinery, so it's a general problem. So a usable SSTO needs to be able to throttle *very* deeply. And that almost certainly means not just individual engines with a large thrust range but being able to cutoff engines as the vehicle depletes its fuel. And that adds complexity, difficulty, and cost to the design and construction. For example, your Titan-II w/ NK-33 SSTO has a mass- ratio of 17.1:1, which means that the peak thrust at burnout would be around 17 gees, give or take. You give a dry weight of about 7,000 kg, and one NK-33 has a thrust in vacuum of abour 167,000 kg-f, so that gives a max g-force of about 24 gees. According to this page: http://www.spaceandtech.com/spacedat...33_specs.shtml The NK-33 has a throttle range of 55 - 104% (the vac. thrust data is from astronautix.com, FYI), so that gives a minimum g-load at burnout of 12 gees. As I said, fairly straightforward but not easy. |
#4
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Why is a LOX/Kero SSTO not rather easy?
In article Pine.WNT.4.56.0308302326280.2728@homecomps,
Larry Gales wrote: So it appears to me that we have had reusable SSTO capability for dense fuel vehicles for a long time. There is little doubt, among those willing to actually look at the facts, that you can get a single-stage expendable into orbit -- at least, with little or no payload -- and have been able to do so for some time. Another example of that (without even exploiting the dense-fuels bonuses) is what you get if you put six SSMEs on the base of a shuttle ET; that one actually should be able to carry quite a substantial payload. The "reusable" part can legitimately be questioned. The assumptions you made about how much various things add to the dry mass are highly debatable. For example, assuming that wings add only 7% is awfully optimistic. It is very difficult to actually *resolve* disagreements about basic assumptions when the battle is viewgraphs vs. viewgraphs. Nothing short of flying hardware will settle such disputes. Claims that LOX/LH2 rockets are inherently difficult and complex to operate were quite persistent for years, but quietly evaporated when DC-X started flying. -- MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | |
#5
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Why is a LOX/Kero SSTO not rather easy?
Larry Gales wrote:
I am not a particular fan of SSTO, but it appears to me that SSTO has long been within our grasp. The best figures that I could get for the Titan II 1st stage (based on Rusty Barton's reply to my earlier post) are a GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of 23.7. Now comparing it to a LOX/kero vehicle powered by something like the Russian NK-33, I see the following plus and minus factors affecting its mass ratio (I am not including a payload in these calculations): The problem is that the NK-33 is a russian engine. NASA would *never* build a craft with a russian engine, and the russians themselves lack sufficient funding to do something interesting with their huge stockpile of fantastic engines. They also lack the technology to build very lightweight fuel tanks. Private (or at least semi-private) entities such as Boeing and LockMart have used russian engines very successfully (Sea Launch and Atlas V), but they are too conservative to develop something revolutionary. So if you can convince someone to build a simple cylindrical design with NK-33 engines, then SSTO with significant payload is quite doable. Reusable SSTO should also be doable if you use vertical landing. And even a VTVL SSTO space transport with zero payload would be very useful since you could use it as a testbed for various technologies and get a quite significant payload by just adding a few booster rockets. The problem is not technical but political. This is kind of sad since most of us s.s.t regulars really enjoy technical discussions like Kerosene vs. LH2, VTVL vs. VTHL vs HTHL, pure rocket vs. airbreather, SSTO vs. TSTO and so on. But such discussions will not get us closer to CATS unless somebody can pony up the money to actually build it. NASA will not do it for us. |
#6
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Why is a LOX/Kero SSTO not rather easy?
Larry Gales wrote in message news:Pine.WNT.4.56.0309042104270.2228@homecomps. ..
On Wed, 3 Sep 2003, Anthony Q. Bachler wrote: Date: Wed, 03 Sep 2003 06:51:48 GMT From: Anthony Q. Bachler Newsgroups: sci.space.tech, sci.space.policy Subject: Why is a LOX/Kero SSTO not rather easy? You cant just 'scale up' a launch vehicle like you scale up a pizza. There are structural factors to consider that are not necessarily linear with vehicle size or weight. You also cant just switch materials without testing. I dont know what problems may or may not arise, but neither do you and that's the whole point. --------------------------------------------------- Yes I do: it is well known that mass ratios become significantly easier as you scale a vehicle up: some things like TPS and insulation scale only as the square of the size, and some other things, such as avionics, pilot, etc scarecly increase, and air resistance is proportionaly much less for large vehicles. This is born out in comparisons of large versus small rockets. Know I *don't* know for sure if this could achive a practical reusable SSTO, but I *do* know that the mass ratio would definitely be easier for a scaled up version. -- Larry My 46-year-long pursuit of cheaper ways of getting into space--born at a reception that I attended at the Soviet Embassy reception during which Sputnik was launched--supports Larry's assertions regarding higher achievable mass ratios as gross mass increases. I feel that current technology could enable a VTOHL space transport having a gross mass of about 750 tonnes or more. But I think that TSTO makes much more economic sense for the near future. TSTO can be much smaller--with proportionately smaller payload, of course. With some TSTO concepts, I think that operations can also be superior to any SSTO that is likely to be practical for a long time to come. Best regards, Len (Cormier) PanAero, Inc. and Third Millennium Aerospace, Inc. ( http://www.tour2space.com ) |
#7
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Why is a LOX/Kero SSTO not rather easy?
"Larry Gales" wrote in message news:Pine.WNT.4.56.0308302326280.2728@homecomps... I am not a particular fan of SSTO, but it appears to me that SSTO has long been within our grasp. The best figures that I could get for the Titan II 1st stage (based on Rusty Barton's reply to my earlier post) are a GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of 23.7. Now comparing it to a LOX/kero vehicle powered by something like the Russian NK-33, I see the following plus and minus factors affecting its mass ratio (I am not including a payload in these calculations): On the minus side, the Titan II 1st stage is not a complete vehicle. It: (a) lacks a nose cone (b) lacks most avionics (c) lacks a cargo bay (d) has 6% denser fueland so has a slightly smaller fuel tank On the plus side: (a) the NK-33 is 420 lbs lighter than the Titan II engine yet it is sufficient for a vehicle nearly 10% heavier (b) the structure does not have to support the 32 ton 2nd stage and so can be significantly lighter. My guess is that those factors mostly cancel out. I also assume that making a vehicle reusable adds about 40% to its dry weight: Wings add 7% Landing gear add 3% TPS add 15% Other add 15% So if we crank those factors in: Dry weight = 10900*1.4 = 15300 lbs Glow = 258000 + (15300 - 10900) = 262400 MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15 Now for the NK-33 we have an average Isp of 331, and given a required dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air resistance, lower back pressure losses, and earlier peak acceleration) we get a required MR of 17.01, which is slightly less than what we can achieve. So we can make orbit with a single stage using very old technology. Of course, this is without payload, but given the fact that the Titan II 1st stage was not optimized for weight (you would not normally optimize a 1st stage) and we have lighter materials today, such as aluminum-lithium and carbon fiber, I would think we would have the necessary margin for a significant payload. We also might fly with a wet wing and eliminate the kerosene tank altogether. And of course if we scaled it up by a factor of 3 we would gain a substantial economy of scale. So it appears to me that we have had reusable SSTO capability for dense fuel vehicles for a long time. -- Larry Please review this thread for another, more detailed, SSTO concept using NK-33s and a wet wing. http://www.google.com/groups?hl=en&l...phi.com&rnum=1 I hope pasting this will work. If not, then I will paste in the entire article. Thanks, BobDL -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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Why is a LOX/Kero SSTO not rather easy?
Larry Gales wrote in message news:Pine.WNT.4.56.0308302326280.2728@homecomps. ..
I am not a particular fan of SSTO, but it appears to me that SSTO has long been within our grasp. The best figures that I could get for the Titan II 1st stage (based on Rusty Barton's reply to my earlier post) are a GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of 23.7. Now comparing it to a LOX/kero vehicle powered by something like the Russian NK-33, I see the following plus and minus factors affecting its mass ratio (I am not including a payload in these calculations): On the minus side, the Titan II 1st stage is not a complete vehicle. It: (a) lacks a nose cone (b) lacks most avionics (c) lacks a cargo bay (d) has 6% denser fueland so has a slightly smaller fuel tank On the plus side: (a) the NK-33 is 420 lbs lighter than the Titan II engine yet it is sufficient for a vehicle nearly 10% heavier (b) the structure does not have to support the 32 ton 2nd stage and so can be significantly lighter. My guess is that those factors mostly cancel out. I also assume that making a vehicle reusable adds about 40% to its dry weight: Wings add 7% Landing gear add 3% TPS add 15% Other add 15% So if we crank those factors in: Dry weight = 10900*1.4 = 15300 lbs Glow = 258000 + (15300 - 10900) = 262400 MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15 Now for the NK-33 we have an average Isp of 331, and given a required dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air resistance, lower back pressure losses, and earlier peak acceleration) we get a required MR of 17.01, which is slightly less than what we can achieve. So we can make orbit with a single stage using very old technology. Of course, this is without payload, but given the fact that the Titan II 1st stage was not optimized for weight (you would not normally optimize a 1st stage) and we have lighter materials today, such as aluminum-lithium and carbon fiber, I would think we would have the necessary margin for a significant payload. We also might fly with a wet wing and eliminate the kerosene tank altogether. And of course if we scaled it up by a factor of 3 we would gain a substantial economy of scale. So it appears to me that we have had reusable SSTO capability for dense fuel vehicles for a long time. -- Larry Please review this thread for another, more detailed, SSTO concept using NK-33s and a wet wing. http://www.google.com/groups?hl=en&l...phi.com&rnum=1 I hope pasting this will work. If not, then I will paste in the entire article. Thanks, BobDL |
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Why is a LOX/Kero SSTO not rather easy?
On Tue, 9 Sep 2003, Christopher M. Jones wrote: Date: Tue, 9 Sep 2003 00:59:16 -0500 From: Christopher M. Jones Newsgroups: sci.space.tech, sci.space.policy Subject: Why is a LOX/Kero SSTO not rather easy? "Larry Gales" wrote: I used that vehicle as a rough proof of concept, but it could never be practical. But if you scale it up to a 3 engine vehicle, then the mass ratio is easier to achive and the peak acceleration is about 4 gees Oh, I'm already well sold on the concept. But it's the "sticky bits" that you have to worry about if you actually want to do it. A 3 engine vehicle won't really solve that due to symmetry and redundancy issues. --- cut/snip --- LOX/Kero on the otherhand has a lower Isp, so SSTOs using it as a propellant have higher mass ratios, around 15 to 20 or so. Factor in the existing throttle range and you're deep in the range of gee loads thought suitable for few other than well trained fighter pilots. And you need a good factor of 2 at least to bring it back to the reasonable range, and that's, as they say, non-trivial. But, it's not an insurmountable obstacle either. The main difficulty right now is that because of the early technical impossiblity of SSTO rocketry, all orbital rocketry has been staged rocketry and the worldwide enterprise of orbital rocketry has focused on solving the problems of staged rocketry. So all the currently existing hardware and experience in rocketry is biased toward staged rocketry. ============================ Oh, I guess the symmetry issue comes after you shut off one engine, which I assume would be the middle engine, then to shut off the next one you would be unbalanced. But can't gimbaling the remaining engine take care of that? After all the shuttle starts off with a massive imbalance due to the off-center location of the tank which chnages in weight throught the flight. -- Larry |
#10
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Why is a LOX/Kero SSTO not rather easy?
On Tue, 9 Sep 2003, Bob wrote: Date: Tue, 9 Sep 2003 10:19:54 -0500 From: Bob Newsgroups: sci.space.tech, sci.space.policy Subject: Why is a LOX/Kero SSTO not rather easy? Please review this thread for another, more detailed, SSTO concept using NK-33s and a wet wing. http://www.google.com/groups?hl=en&l...phi.com&rnum=1 I hope pasting this will work. If not, then I will paste in the entire article. Thanks, BobDL -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- ===================== Thanks a heap -- I remeber that article and have looked in vain for it for a while. Much appreciated -- Larry |
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