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Post by Lensman on Mar 3, 2005 8:52:17 GMT
Excpet that frankly your systems are -more- complex than ours, and ours -are not- barred by the novels... None of my systems are anywhere near as complex as a liquid fueled rocket system, which is one of the most complex and accident-prone things we humans have ever built. Admittedly the way airbag systems are built into cars are complex. Using compressed gas to cushion the fall of a capsule inside a tube could be a much simpler design. Anyway, go back and read what Verne proposed to cushion his passengers in From the Earth to the Moon. What I propose is much simpler, as well as much more effective. I've repeatedly shown where your proposal directly contradicts what the novel states, as well as implies, in many places. If you don't agree, then I think it's time to say we're going to have to agree to disagree. |
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Post by Topaz on Mar 3, 2005 9:14:42 GMT
But you haven't answered my point that if they had a retro rocket system, they would have used it to make a controlled landing, and would have picked their landing places. There is no way to reconcile that with the text. The landing of the 5th cylinder clearly describes a meteoric landing. In fact, to interpret it any other way would require that for some reason the Martians deliberately faked a meteoric landing. Nor have either you or Lanceradvanced addressed my point about the first and second cylinders not landing near each other. My point was only dismissed, not actually responded to, earlier in this debate. Clearly the Martians, from their actions, were very concerned for their safety upon the initial landing. If they could have landed the first two cylinders near enough for each other for mutual support, they would have done so. They didn't because they couldn't. They couldn't because they couldn't control their landing places. I agree with you completely on that latter point. Even with all our guidence and navigation technology, and including a soft-landing system, the NASA couldn't tighten up the projected landing ellipses on the MER rovers down much smaller than 8 x 30 miles. I'm sure the Martians could do better, but considering they landed the first two cylinders within 'walking distance,' I'd say they were doing pretty darn good!  As for the details of the 5th cylinder landing, that bears a close examination. When we look at what's said and don't allow ourselves to look at implications, the situation isn't quite as clear. We see a bright green flash. There's a huge concussion. After that, the house collapses and the Narrator does a good Superman-in-flight imitation until his head contacts the oven, resulting in unconsciousness. After he awakens, he describes the scene: The cylinder had landed in the house across the street. Then comes the pivotal passage: "The earth all round it had splashed under that tremendous impact - "splashed" is the only word - and lay in heaped piles that hid the masses of the adjacent houses. It had behaved exactly like mud under the violent blow of a hammer." Okay, I'll grant that Wells intended to describe an unbraked, high-velocity impact. That is, no doubt, what he had in mind. If we want to confine our discussion to just the work as literature, then that's enough and we stop there. However, that doesn't make it possible in the real world, which is where, I believe, we've taken our discussion. In that context, we don't know the landing of the cylinder itself actually caused the crater and the 'splashed' earth. There was a flash, a concussion, then the Narrator was unconscious. He wasn't around to observe the rest, and I doubt the Curate was much of a scientific observer and it's all moot, as we don't ever hear his description of the event. Any mechanism that simultaneously provides the Martians a safe landing and duplicates this series of events and effects is an adequate solution. Any of our solutions fit the secondary criteria - they all produce the same description of the landing from the point of view of the Narrator: 1) Lensman Aerodynamic braking only from entry into the atmosphere, green glow from ablative heat shield, crater and 'splashing' forms from high-velocity impact. 2) LancerAdvanced Retrofire brakes the cylinder to some fairly low altitude, probably providing the green glow/flash. Free-fall from burnout provides enough impact to create a crater and 'splashed' earth. 3) Topaz/Bayne Retrofire brakes the cylinder to a soft landing, inside a crater produced by a penetrator explosive shot ahead when on final approach. Retrofire provides the green flash, the crater and 'splashed' earth are provided by the explosive missile. I have to agree with Lancer that a 'meteoric' impact of a 90' wide cylinder would probably do more than partially collapse a house across the street from 'ground zero.' Maybe we're wrong about that, but there's a lot of energy in that kind of impact!  I also think I've adequately demonstrated that such an impact isn't survivable to the Martians, although you might still disagree on that score. Lancer and I differ on where we'd put the extra mass and mechanism in our systems - He splits the system into a smaller retro system and then a crushable nose, whereas I put all my braking into just a retro system and take it all the way to a soft landing. Either provides a survivable landing, depending on the speed required to make a suitable impact crater, of course. I wish I had the knowledge to do the soil mechanics analysis to figure that out. A retro rocket system would require large rocket nozzles. They would have been seen if they were on the back of the cylinders. If they were on the front, there would have been the problem of lack of stramlining, likely causing the cylinder to tumble as it came in, plus unless the cylinder really had a soft landing, there'd be the danger of explosion. I think we all know just how susceptible liquid-fuel rockets are to exploding upon impact. This is not a good design-- to put it mildly!-- and the fact that none of the cylinders exploded upon landing is a strong indication they didn't make a crash landing with a rocket on the front of the cylinder. Well, we're only assuming the egress hatch end of the cylinder is the 'back' during launch. It just as easily could have been the top, with the rockets at the other end, and protected with a fairing during launch like our expendable rockets. Large nozzles aren't visible if they're at the bottom of the pit! Conventional engine bells like you'd see at the bottom of a Saturn, Delta, or Shuttle would not survive entry, let alone being faced into a supersonic flow during descent, unless you're talking about the system Lancer talked about earlier in which they're kept running the whole time. However, scroll back a page and take another look at the truncated aerospike engine I drew out earlier. This is a system specifically designed to survive a re-entry faced into the airflow. The other option is to put them back up near the other end of the vehicle, near the hatch but still firing forward, but this would make them visible after landing. Since a bare cylinder is an unstable aerodynamic shape, all of our proposals would require some kind of active RCS to keep the right end going forward, whether there's an engine at one end or not. Eithe that or fins (also visible after landing) or spin-stabilization, which results in dizzy Martians.  I'm proposing a very soft landing, so I'm not worried about explosions. Lancer's system could expend all fuel at the point of burnout, so there's nothing left to explode. The other factor depends on the propellants used. If it's oxygen/hydrogen, then rupturing the tanks would result in a fireball, but not a detonation. To use the Challenger as an example, it was the aerodynamic forces of the vehicle peeling away from the disintegrating stack that destroyed the orbiter, not the explosion itself. You know, we're getting dangerously close to being able to do a first-order design study for not only the cylinder, but also the gun system itself, since we're starting to know so much about the cylinders. If we're agreed on Martian G-tolerance levels, I'd be tempted give that a shot, if you'll pardon the pun. ;D |
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Post by Lensman on Mar 3, 2005 9:15:16 GMT
landing a ship "on it's jets" so to speak is something we haven't tried yet, Sure we have: The moon landings. Which, of course, didn't have the problem of entering thru an atmosphere and having the ship's exhaust being blown back to sear the outside of your own spacecraft. But OK, I concede the point, with the system Topaz showed a picture of-- really interesting BTW, I hadn't heard of anything like that-- it's possible that the Martians could have used retro rockets that fired all the way down to the ground. (But no, not solid fuel, you can't jettison the fuel that way. Unless you use "hybrid fuel" like SpaceShipOne. Which of course, they could have.) Could have-- but from the novel's text, it's clear they didn't. They're not "faking" a metoritic landing, they're just makeing a -very limited- one, involving moving just enough earth to bury the cylinder, Boy, you're just not gonna concede any of my points, are you? Wells very clearly described the earth splashing, he made a big point of it: "It had behaved exactly like mud under the violent blow of a hammer." This is most definitely not "just enough earth to bury the cylinder." If you're not gonna concede any of my points, then you're not "playing fair," so what's the point of having this discussion? |
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Post by Lensman on Mar 3, 2005 9:21:30 GMT
If the martians were coming in completly uncontoled, why did none of them hit a rock outcropping and get smashed? or land in a lake or pond? Maybe they did. Wells describes three more cylinders being launched than he describes landing. The usual interpretation is that since Wells was writing a serial, he forgot. But if we assume this is a "true account" then the implication is they didn't survive. Smashed and lost in the woods or mountains, or landed in the water... |
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Post by Topaz on Mar 3, 2005 10:04:10 GMT
The truncated aerospike is a really neat system. Just amazing in its simplicity and elegance. It's a pity the system never got a chance. The system as-designed at the time used either LOX-Kerosene or LOX-Hydrogen. They hadn't really developed hybrids back then.
The DC-X would've made a perfect platform to use this engine.
I do want to reiterate the point that all of this is in good fun, and I'm sure you both feel the same. Yes, we've tossed some stuff back and forth fast and furiously. In the end, however, I've enjoyed the discussion immensely, as well as seeing that we could do it without the 'usual' acrimony one might see in other topics.
I haven't dusted off my old textbooks in ages! Thank you both for keeping me honest and making me attempt to prove my points! ;D
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Post by Bayne on Mar 3, 2005 10:11:27 GMT
[glow=red,2,300]I still like the idea of a ray or explosive used as part of the dedceleration and to blast a pit for the cylinder to land into.
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Post by Topaz on Mar 3, 2005 10:12:37 GMT
You can't, without knowing how long it took to declerate... but the basic equation will be something like... (D/T)/G=X where T=(Sum of the Series of the Square of the Time) or... 1.5*(T)/9.8 = X (done in tidy meters/sec) That's interesting. I double-checked my reference and the formula I'm using appears to do just that. Isn't the time term in the speed/distance portion cancelled out by couching the result in terms of g, which itself contains a time element? Math wasn't ever my strong suit, but like any good engineer, I plug in values and grind out results with the best of 'em. One of my old professors used to say that the best skill you'll ever have as an engineer is to know where to find the formula you need, not how to derive it. ;D ;D "(man,I hate doing physics problems in english units)" Oh, amen. Unfortunately, they doomed us here in the US when they tried to teach metric solely by making people rote-learn the conversion from Imperial units!  |
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Post by Lensman on Mar 3, 2005 10:56:10 GMT
Yes, the water converts the increased weight into hydraulic pressure. Unfortunately, if the load on the bottom half of your body was effectively 'halved' as you're saying, your body still is pushing down with the entire force and your body would sink, and quickly. See now, when you say things like that it makes me think you don't understand the principles involved. The human body has approximately neutral buoyancy. If subjected to high G's, the human floating in water doesn't sink, because the water is subject to the same G force as he is, and therefore provides greater buoyancy. I finally figured out how to "model" this case in my head. Hal Clement wrote a famous, classic science fiction novel, "Mission of Gravity". It's set on Meskelin, a planet which has about 3 G's at the equator, and hundreds of G's at the poles (the planet is very large and heavy, but spins VERY FAST, you see...) So immersion in a water tank under high acceleration would be like swimming in the sea on Meskelin. I was trying to figure out: Would the G forces "magically" be converted to hydraulic pressure, reducing the amount of pressure on the body in the direction of acceleration? No. Swimming in the sea of Meskelin doesn't magically reduce the amount of gravity your brain (and every other part of your body) is subjected to. Or to put it more simply: buoyancy just means you float, it doesn't negate gravity. Perhaps that was obvious to you, but I had a hard time coming up with a definite answer in my own mind. Hey! Thanks very much, Topaz! I bookmarked that site. Several times I've had occasion to wonder just what the limit was on G forces the human body could tolerate. I'd take the eye damage Col. Stapp sustained as the most telling limit. The other injuries were apparently caused by the safety harness plus his limbs (and head) flying around unsecured. That's because he experienced both acceleration and deceleration facing the same direction. If his acceleration couch had protected him in both directions, I don't think he would have had those injuries. The Martians won't have that problem. So the real limit seems to be higher than 35 G's but less than 46 G's. So, about 40 Gs for humans, rather less for Martians. I don't like the idea of coming in at maxium G-tolerance - it's too big a risk and doesn't have any kind of safety factor. I don't either. You'd lose some crew that way, either dead or incapacitated. And considering the very low number of Martians that arrived on Earth, you can't afford to lose many. 716 feet Which is, of course, longer than the cylinder. Aha! Thank you again, Topaz! So I'm within an order of magnitude of survivability. In fact, I think you ignored the stopping distance of the cylinder, so I think actually I'm within a factor of 2. That's a heck of a lot better than Verne's original design! Of course, a 600 mph terminal velocity assumes a very significant amount of aerobraking. And as has been pointed out in this thread, that's hard to do with an object as massive as the cylinder Wells described. So, after all this "sturm and drang," I have to conclude: If I actually want to be able to say my design is mathematically defensible, I need to "tweak" my design in some fashion, or else find a completely different approach. If I had one of those "intellects vast and cool and unsympathetic," perhaps I could!  OTOH, if all I want is a system which will -- in the words of the immortal W.S. Gilbert-- "give artistic verisimilitude to an otherwise bald and unconvincing narrative," then I'm already there!  |
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Post by Lensman on Mar 3, 2005 11:16:20 GMT
I, for one, think that forming the initial pit/crater as a 'foxhole' does provide a tactical advantage. Yes, it prolongs cooling, but keeps the cylinder out of direct line-of-sight of outside observers for all landings after the first one. That's important because after the first landing, we'll know they're hostile and we'll likely try to fight back. Actually, as I said, altho perhaps not in this thread, to destroy the Martians you don't require the military, only some farmer with a few sticks of dynamite. Wait until the lid falls off, then immediately light a few sticks and chuck them in. And your "foxhole" does absolutely nothing to protect you from this. Which would be better: Coming in for a soft landing in a clearing in the woods (or any location far from a densely inhabited area), and immediately securing the area? Or announcing your arrival with a huge bang and tons of earth thrown around, then burying yourself and making it impossible to move or look at your surroundings for half a day? Ask any military tactician, and I'll bet I know what he'd say. |
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Post by Topaz on Mar 3, 2005 11:26:20 GMT
See now, when you say things like that it makes me think you don't understand the principles involved. The human body has approximately neutral buoyancy. If subjected to high G's, the human floating in water doesn't sink, because the water is subject to the same G force as he is, and therefore provides greater buoyancy. Quite possibly. I'm a little fuzzy on that area, as it's been years and hydraulics was far, far from my areas of training in the first place, after my basic classes. I think you're probably right on the buoyancy matter. Still, I think we're agreed on the implications of soft-tissue injuries due to G-effects, which put an upper limit on G-tolerance regardless of how one suspends the body. You're welcome about the link. A really interesting article! Aha! Thank you again, Topaz! So I'm within an order of magnitude of survivability. In fact, I think you ignored the stopping distance of the cylinder, so I think actually I'm within a factor of 2. That's a heck of a lot better than Verne's original design! Actually, I didn't (it's the 270' part of the 275'), but to be within an order of magnitude on a first-order design study is not a bad place to be at all! Hell, there were days in my classes where I would've given my left arm to be that close! ;D BTW, are you cool with the 15G maximum tolerance for the Martians? Less safety factor, of course. I was serious about taking a crack at the gun design. I know the caliber of the gun, the value of g on Mars, and the escape velocity (thanks Lancer!). I think we're all agreed on the G-tolerance of the Martians. I'm starting to think I can estimate things like the cylinder weight, total impulse required and the pressure in the gun to accelerate at the right G-factor to keep the Martians safe. From there I may be able to derive estimates for things like barrel length, launch angle, and even a propellant weight for the cylinder to complete the boost to escape the planet. |
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Post by Topaz on Mar 3, 2005 11:29:59 GMT
Which would be better: Coming in for a soft landing in a clearing in the woods (or any location far from a densely inhabited area), and immediately securing the area? Or announcing your arrival with a huge bang and tons of earth thrown around, then burying yourself and making it impossible to move or look at your surroundings for half a day? Ask any military tactician, and I'll bet I know what he'd say. Oh, of course. Unfortunately, a certain writer stuck us with Martians in a pit. As long as I have to have one, here are some good uses I can develop for the thing! |
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Post by Lensman on Mar 3, 2005 12:49:39 GMT
I have to agree with Lancer that a 'meteoric' impact of a 90' wide cylinder would probably do more than partially collapse a house across the street from 'ground zero.' Well now, I admit I didn't realize the other house was that close. The novel says "We then crossed to a place where the road turns towards Mortlake. Here stood a white house..." (Book 2, Chapter 1) Later it says "The earth all round it [...] lay in heaped piles that hid the masses of the adjacent houses." (Book 2, Chapter 2) The latter passage led me to believe the other house was a short distance away, but not right across the street. I see the former passage might be interpreted to suggest it was, but not necessarily. Is there another passage which states or suggests it's right across the street? I don't know exactly what the destructive effect would be upon being that close to a massive meteorite impact. But then, neither did Wells. Presumably most of the force would be directed upwards, but the concussion wave would still be pretty terrific. I also think I've adequately demonstrated that such an impact isn't survivable to the Martians, although you might still disagree on that score. I agree the numbers we chose for our estimates showed that, if the Martians were as fragile as evolution on a .4 G world suggests, then-- using the numbers in the rough estimates we chose-- the Martians would have been injured by the impact. Change the assumptions-- for instance, a lower speed impact, or the Martians have genetically designed a tougher strain, better able to resist G forces-- then they can survive. Will you agree that, if the Martians can get their terminal velocity down below supersonic speed, that my system for deceleration comes a lot closer to being mathematically defensible than you thought before you did the math? Conventional engine bells like you'd see at the bottom of a Saturn, Delta, or Shuttle would not survive entry, let alone being faced into a supersonic flow during descent, Which is one of the reasons I had rejected the entire concept of retro rockets which burn all the way down, or even most of the way. However, scroll back a page and take another look at the truncated aerospike engine I drew out earlier. This is a system specifically designed to survive a re-entry faced into the airflow. Yes, that's quite clever, and thanks again for the info! And yes, after reading that I will concede that it is reasonable to suppose the Martians *could* have used that for retro rockets during re-entry. Just as the Egyptians *could* have done any number of things to make it easier to build the pyramids-- like using wheeled vehicles, or casting concrete-- but there's no evidence they *did* that. Since a bare cylinder is an unstable aerodynamic shape, all of our proposals would require some kind of active RCS to keep the right end going forward, whether there's an engine at one end or not. Eithe that or fins (also visible after landing) or spin-stabilization, which results in dizzy Martians. I was initially imagining having to use spin-stabilization, and thinking about what problems that would entail, but then I realized the large gyroscopes I had already mounted inside the cylinder would serve to spin-stabilize it. I can't believe no one likes my gyroscopes. ::pout:: Such an elegant solution to multiple problems, and so Victorian to boot! (Altho the Martian design would be a bit different; they don't use the wheel, so they'd use weighted pivoting arms instead of wheels.) If it's oxygen/hydrogen, then rupturing the tanks would result in a fireball, but not a detonation. To use the Challenger as an example, it was the aerodynamic forces of the vehicle peeling away from the disintegrating stack that destroyed the orbiter, not the explosion itself. My understanding is the Shuttle's main tank is the world's largest chemical bomb. And that during the Challenger explosion, it went off. I don't understand how you can characterize it as "not a detonation". Does the shuttle use liquid hydrogen? That's a relatively low-energy fuel for its mass, admittedly, but if you ever did that chemistry lab experiment where you electrolyze water into oxygen and hydrogen, then stick a glowing wood splint into the test tube filled with hydrogen, the sharp "tink!" you hear certainly *is* an explosion. You know, we're getting dangerously close to being able to do a first-order design study for not only the cylinder, but also the gun system itself, since we're starting to know so much about the cylinders. If we're agreed on Martian G-tolerance levels, I'd be tempted give that a shot, if you'll pardon the pun. ;D I don't know that we're agreed on *anything*, but I'd certainly like to see you give it a shot anyway! Just because I have my own "pet" design doesn't mean I'm not interested in discussing others' designs. If you're thinking about the space gun, I'd like to know what you think about the Christopher Bishop launch propellant design (using a heat ray to heat ice into expanding gasses) as opposed to Verne's guncotten propellant, which is said to be unworkable in Earth's gravity. The critique I've read is that Verne's space cannon would flatten the passengers into paste "without sending the capsule higher than the surrounding trees." As I said when I first mentioned this, I'm not sure why the math doesn't work, but I'm guessing the expansion of the gasses peters out much too quickly. If that's the problem, then using the heat ray to convert ice to heated gas at a fixed rate of speed would overcome the problem. But that creates its own problem of the heat ray expanding with distance. I have thought of one solution to that, but it's not elegant, and I'd like to know if anyone else can come up with something that is elegant. Of course, we could just assume they have a heat ray "laser" but I think that's a bit of a cheat. |
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Post by Lensman on Mar 3, 2005 12:59:25 GMT
I still like the idea of a ray or explosive used as part of the dedceleration and to blast a pit for the cylinder to land into. Hmmm... that's an intriguing idea. In another thread, they proposed using the heat ray as a "combustion-less" propulsion device by heating the air inside a rocket propulsion chamber, thus creating a fuel-less rocket. If that would work, that suggests the Martians may have been able to do something similar to slow the cylinder. And that would be a more elegant solution than my proposal for an erstwhile parachute, too! It doesn't explain the green glow, however. |
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Post by Lensman on Mar 3, 2005 13:17:43 GMT
Actually, I didn't (it's the 270' part of the 275'), Oh, double-fudge! Here I thought I was getting close.  BTW, are you cool with the 15G maximum tolerance for the Martians? Less safety factor, of course. I was serious about taking a crack at the gun design. Well you certainly don't need my permission! While I'm unwilling to concede anything which I don't believe I absolutely have to which will make it harder for my design to work, I will certainly conced that if the Martians didn't breed a strain of their race better able to withstand Earth's gravity, and if it is appropriate to assume their G tolerance is proportional to ours, then they wouldn't design something which had more than 15 G's. However, if we assume the Martians practice genetic engineering-- and I do-- then it's just as reasonable to suggest they bred their invaders to be better able to withstand Earth's gravity. Yes I know Wells describes them having problems breathing and moving around. But think of how long any of us would survive living in a 2.5 G environment. Heart attack, anyone? |
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Post by Topaz on Mar 3, 2005 18:29:13 GMT
Well now, I admit I didn't realize the other house was that close. The novel says "We then crossed to a place where the road turns towards Mortlake. Here stood a white house..." (Book 2, Chapter 1) Hmm, yes. Perhaps "across the street" isn't supported by the text after all. Still, it would have to be within line-of-sight of the later house, since he describes the landing site quite exactly. From the few English villages I've seen, that would have to be quite close by, given the twisty streets. Change the assumptions-- for instance, a lower speed impact, or the Martians have genetically designed a tougher strain, better able to resist G forces-- then they can survive. Will you agree that, if the Martians can get their terminal velocity down below supersonic speed, that my system for deceleration comes a lot closer to being mathematically defensible than you thought before you did the math? Absolutely. Frankly, my original thought was that the value would be in the hundreds, if not thousands of G's. I was rather surprised we could get it down to 43G's for a 600mph impact! I suppose this begs the question as to what speed would be survivable. Rearranging my trusty formula yet again... V safe = SQR(G safe*d*29.914) (SQR is my shorthand for 'square root') From our previous discussion, G safe = 12.2 d = 275' So... V safe = SQR(12.2*275*29.914) V safe = SQR(100,361.5) V safe = 316.8 mph Get the speed down to that and I'll concede your point. While it'd still be a heck of a whallop, they'd stand a good chance of surviving. Oy, I lost the rest of your quote. Moving on to a separate post! |
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Post by lanceradvanced on Mar 3, 2005 18:31:36 GMT
Which, of course, didn't have the problem of entering thru an atmosphere and having the ship's exhaust being blown back to sear the outside of your own spacecraft. Which is why I didn't include them... or the viking landers either, and again, if you loose your speed -before- you hit the atmosphere, then having the exhaust "blown" back isn't an issue. Also, the moon landings only had to deal with the velocity of a lunar orbit, and 1/6 the gravity. The closet we've come to doing it on earth are a few test flights of the DCX. It's simple.. the two -arn't- contridictory, what splashed out of the way was about the volume of the cylinder, which given Topaz's 30 x 90 yard size is about sixty thousand cubic yards of dirt... which is enough to pile earth up 10 feet high, for almost 50 yards around the cylinder. In a pure metoritic impact the earth wouldn't have just "splashed" it would have -exploded- outward, probably digging a quarter mile crater... |
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Post by lanceradvanced on Mar 3, 2005 18:41:28 GMT
None of my systems are anywhere near as complex as a liquid fueled rocket system, which is one of the most complex and accident-prone things we humans have ever built. . To quote, the guys at Armidillo Aerospace, "Rocket Science isn't complex, it's just not -common-" we've been building the things for over 3/4 of a century now, and when it comes down to it, they're a fuel pump, nozzle and tanks, they're nowhere near as complex as the systems on a helicopter for example. Yes, they blow up rather spactucularly when something does go wrong, but so do bridges, buildings and jet aircraft. Solid fuel rockets are even simplier, and I don't see any good reason to rule them out, either... |
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Post by Topaz on Mar 3, 2005 19:13:35 GMT
Yes, that's quite clever, and thanks again for the info! And yes, after reading that I will concede that it is reasonable to suppose the Martians *could* have used that for retro rockets during re-entry. Just as the Egyptians *could* have done any number of things to make it easier to build the pyramids-- like using wheeled vehicles, or casting concrete-- but there's no evidence they *did* that. I suppose we'll just have to disagree there. I don't see either Lancer's or my own proposals contradicting the letter of the text. The spirit of the text, as Wells intended it, certainly, but that became okay for me the moment we took this into the 'real world.' I was initially imagining having to use spin-stabilization, and thinking about what problems that would entail, but then I realized the large gyroscopes I had already mounted inside the cylinder would serve to spin-stabilize it. I can't believe no one likes my gyroscopes. ::pout:: Such an elegant solution to multiple problems, and so Victorian to boot! (Altho the Martian design would be a bit different; they don't use the wheel, so they'd use weighted pivoting arms instead of wheels.) On the former point, I have only one thing to say: Dizzy Martians. As for gyroscopes, they're great. The ISS uses them for stabilization most of the time, as a matter of fact. Unfortunately, gyros large enough to overcome the kind of aerodynamic moments generated as the cylinder enters the atmosphere would (probably) be absurdly large and heavy. An RCS system does the job with much less weight and space. I won't disagree that gyros would be highly useful for the trip to Earth - saving RCS fuel - but those could be quite small and light, by comparison. My understanding is the Shuttle's main tank is the world's largest chemical bomb. And that during the Challenger explosion, it went off. I don't understand how you can characterize it as "not a detonation". Does the shuttle use liquid hydrogen? That's a relatively low-energy fuel for its mass, admittedly, but if you ever did that chemistry lab experiment where you electrolyze water into oxygen and hydrogen, then stick a glowing wood splint into the test tube filled with hydrogen, the sharp "tink!" you hear certainly *is* an explosion. I've read an analysis of the accident. When the leak in the SRB burned through its lower supports, the whole thing pivoted forward and nose-inward on the forward support, crushing the upper part of the main tank. That structure failed, dumping the propellants into the atmosphere and they ignited, creating the huge fireball you saw. When the forward part of the tank failed, the front strut to the orbiter was cut and the entire orbiter pivoted back - nose outward - on the rear two supports near the main landing gear wells. The angle to the (supersonic) relative wind increased until the aerodynamic loads exceeded the structural limits of the orbiter. The wings came off (left first, IIRC), then the orbiter tumbled and broke up as airflow crushed the payload bay doors and tore the fuselage structure apart. The crew cabin broke free and was destroyed upon impact with the water, about two minutes later. The fireball from the propellants certainly created an explosion, but not a detonation which would've created a strong blast wave. Basically the propellants were simply dumped from the tank and ignited by the still-burning rockets, so the difference from your lab experiment is that the propellants were largely still liquid and not an optimum mixture of gasses like you saw in your test tube. Because of the LOX, the burning was very rapid, but essentially no different in principle than the destruction of the Hindenburg, from which people walked away after the structure landed on the ground. Think of tossing a jar of gasoline into a torch - you'd get a big fireball, but not the detonation and blast wave that an optimum mixture of vaporized gasoline and air would produce. If you're thinking about the space gun, I'd like to know what you think about the Christopher Bishop launch propellant design (using a heat ray to heat ice into expanding gasses) as opposed to Verne's guncotten propellant, which is said to be unworkable in Earth's gravity. The critique I've read is that Verne's space cannon would flatten the passengers into paste "without sending the capsule higher than the surrounding trees." As I said when I first mentioned this, I'm not sure why the math doesn't work, but I'm guessing the expansion of the gasses peters out much too quickly. If that's the problem, then using the heat ray to convert ice to heated gas at a fixed rate of speed would overcome the problem. But that creates its own problem of the heat ray expanding with distance. I have thought of one solution to that, but it's not elegant, and I'd like to know if anyone else can come up with something that is elegant. I've done a little initial research already and any kind of 'conventional' gun isn't going to cut it, much for the reasons you state above. To get enough total velocity out of the gun, there'd be an initial G-load 'spike' at the beginning of the launch that would kill the occupants, then slowly taper off to zero at the moment the cylinder leaves the muzzle. This is because you have one charge of gas that is expanding to propel the cylinder. The pressure (and therefore the pushing force) is very high to begin with, then tapers off as the projectile moves down the barrel and the gas expands, reducing the pressure. Any system that's going to meet the requirements has to keep adding gas to the gun to keep the pressure relatively constant, and so keep the G-loads lower and also fairly constant. I've started working up a hybrid of staged combustion and light-gas guns. More to come as I have a little time to put the information together. |
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Post by Topaz on Mar 3, 2005 19:20:04 GMT
Well you certainly don't need my permission! No, but I save needless discussion if we're all on the same page to begin with! ;D Anyone else have any objection to 15G maximum, 12G 'safe' values for the Martians? |
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Post by TOMAHAWK on Mar 3, 2005 22:58:04 GMT
I wonder if the supagun had rifling!!! - the problem is wouldn't the cylinders start tumbling as soon as they left the "GUN", now i have noticed post stating that they maybe had retros/control jets for attitude control ....
hmm ...it would take monumental control inputs to correct a cylinder that is tumbling around in space, look at the film Apollo 13 when the astronauts are trying to maintain the booster/lander in steady flight ...I don't know if that would be possible in say a 200ft cyclinder at planetary escape speed.
also .... Is it feasable that they could have gone into orbit first (using retros to slow ) and then entered out atmosphere like Our Space shuttle ...the only problem I have is stability (but this would then allow them to "Pick" or fine tune their landing area ie GB!!)
any thoughts on the question of stability ...Unless it had drop off wings or retractable wings, i dunno ...(It may be unsafe to assume the cylinders that landed were actually FIRED off in that form)!!
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I also think I've adequately demonstrated that such an impact isn't survivable to the Martians, although you might still disagree on that score.
