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Post by Lensman on Mar 6, 2005 5:58:01 GMT
Comes complete with free martian soft toy, photo of you on ride and a souvenir sick bag. LOL! Thanx for injecting some humor into this perhaps overly-serious thread, Horsell.
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Post by Lensman on Mar 6, 2005 6:00:45 GMT
l Get your souvenier piccy of yourself being drained of blood by the HM only £5 ROTFL!! As the thread rapidly sinks in the west...
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Post by Lensman on Mar 6, 2005 6:04:11 GMT
just how did the martians stop, what was to stop them ploughing 50/100 ft down into the Earth, they would be pretty chuffed at that But they did plow down into the earth, and the tip of the cylinder (which we're presuming to be bullet-shaped) plowed in a lot farther than any measly 100 ft. About the length of the cylinder, or even somewhat more depending on how deep you think the pit is.
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Post by Lensman on Mar 6, 2005 6:13:52 GMT
I don't have a problem with them coming in at a few hundred miles an hour, that only takes free fall from a mile or so up, but the "uncontroled" descent with aerobraking, even if combined with shock absorbant couches, and some other shock absorbing system, simply isn't adequte to slow them to that degree. As I said rather recently in this thread, we all agree the cylinder must have slowed considerably before impact, losing the vast majority of its speed, which as has been pointed out is not the escape velocity from Mars, but rather the fall-to-Earth-from-infinity velocity, about 25,000 mph. The difference between 1000 mph and 0 mph is only about 4% of the total velocity. So all our argument is over that small difference, plus the method used to achieve the slowing.
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Post by lanceradvanced on Mar 6, 2005 14:50:59 GMT
I didn't remember they were gyroscopically stabilized, but if so then perhaps we can refute Topaz' assertion that using gyros for stabilization would take up an unreasonably large amount of the cylinders' internal space.. There is a second way to use a gyro to stabilize, that's to hook a -small- gyro to the control systems of the craft, the gyro remains at an even keel, and as the plane pitches, it the comparitive movement againts the gyro's actuates the controls to counteract the movement.
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Post by Lensman on Mar 6, 2005 23:32:40 GMT
There is a second way to use a gyro to stabilize, that's to hook a -small- gyro to the control systems of the craft, the gyro remains at an even keel, and as the plane pitches, it the comparitive movement againts the gyro's actuates the controls to counteract the movement. That's a good point, thanx.
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Post by Lensman on Mar 11, 2005 0:32:58 GMT
Topaz: If you're still working on the Martians' space gun model, you might be interested in the following: ~~~~~~~~~~~~~~~~ I read with utter incredulity Alex Eisenstein's statement (p306) that "Cavorite...is the kind of 'impossibility that cannot easily be demonstrated—whereas Verne's cannon could have been demolished on paper at the time he wrote." The truth is almost the exact opposite. The theoretical basis of Verne's gun is perfectly sound, though it could not have worked as he described because of air resistance. Willy Ley (Rockets, Missiles and Men in Space, ch. 10) discusses the modifications (mountain site, evacuated barrel) that Oberth and von Pirquet proposed to overcome this problem. I suspect that with modern technology, and a location on Everest, such a gun could be built. It is interesting to note that the 119 foot long HARP 16-inch gun operated in the late '60's on Barbados by McGill University launched two hundred pound research payloads from sea level at over a mile a second. (And, incidentally, used an evacuated barrel.) Although this is only a seventh of escape velocity, a space-gun would be several thousand feet long and would use multiple charges—exactly like the almost horizontal guns the Germans were building to shoot across the English Channel in 1944. ~~~~~~~~~~~~~~~~ from: www.depauw.edu/sfs/backissues/6/notes6.htm
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Post by Topaz on Mar 14, 2005 9:21:17 GMT
Hi guys, Lensman, thanks for the info. That's a very interesting link. Yeah, I'm just getting over being sick and I've been doodling around with the space gun thing a bit in the last couple of days. Mostly, it seems to be a case of how long a gun one is willing to tolerate. You can either go for a long gun and relatively smaller booster capability from the cylinder, or use the gun as a simple 'cold-launch' tube for a primarily booster-powered launch vehicle, much as the Soviets liked to launch their later ICBM's like the SS-18. Either way you almost certainly need the cylinder to have some ability to thrust once launched because of the fixed nature of the gun, which I'll go into later. In any case, I agree with the assessment that some kind of multiple-charge gun is required. I'd already posted a link to the German WWII 'V-3' earlier, and that's the sort of thing that's required. I'll try to post some preliminary cylinder specs as a starting point tomorrow. You're not going to believe how heavy that cylinder is!
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Post by TOMAHAWK on Mar 14, 2005 22:11:16 GMT
Something doesn't pan out .. A shuttle/rocket launch the 'g' builds up gradually ...to launch out of a large gun ..the G would bang in AT EACH section that fires ..ie each charge to build the speed for the cylinder (super gun/german gun V3 operation were there is a charge at various sections along the gun) infact the G/speed would bang in STRIGHT AWAY as soon as the button was pressed for launch .... The occupants simply would not survive the RAPID build up of G force. Also just what the hell type of charge actually started the cylinder off ...jeez it had to be HUGE, bearing in mind the breech of the gun was buried ...what the heck happened to the recoil and exhaust gas ...wouldn't s simply blow the entire gun/breech to bits....How much explosive would that have taken? ?? Also ..how think was the cylinder, bearing in mind it's hollow and there has got to be a massive build up of heat in the bore of the gun..i expect it had to be a snug fit...no it HAD to be a snug fit ....so I would love to know just how it stopped itself WELDING to the inside of the bore. I can think of simpler ways to launch an invasion force...the martys certainly made life difficult for themselves
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Post by lanceradvanced on Mar 14, 2005 22:31:59 GMT
Something doesn't pan out .. A shuttle/rocket launch the 'g' builds up gradually ... The -speed- builds up gradually, G-forces pile high pretty quickly, and then -ease- G is acceleration, not speed.... but yes you would get repeated shocks, but each could go off a little behind the shhell to soften things, with a multicharge gun, but if you staged them out each shock could be less that the g-force astronaughts expereince on liftoff. As for techical concerns, you just build the gun that much bigger/stronger, deeper into the ground.,, heck , yo don't even nesc have to make it a breachloader, lower the cylinder into the barrel to load it. The major advantage of a space cannon, if you have the resources to build it is that it's a) reusable and b) it's a "leave your fuel at home" concept, you can build it to boost -big- payloads, because it doesn't have to lift -itself- as well... There have been argubaly -crazier- lauch systems proposed, from Laser Lift, to Orion Drives, "King David's SpaceShip" features a victorian level planet that needs to get a ship to orbit, they build a orion type ship, that used conventional explosions... now -that- was a rough ride...
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Post by TOMAHAWK on Mar 14, 2005 23:27:40 GMT
i assume you mean conventional to mean Nuclear ... wasn't the Orion 'powered' by detonating nuclear bombs behind it to push it forward
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Post by lanceradvanced on Mar 15, 2005 4:22:52 GMT
i assume you mean conventional to mean Nuclear ... Nope.. they had victorian level tech, so no nukes, just a lot of guncotton (the book wasn't specific on what the used) Orion doesn't -need- nukes, just explosions
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Post by Topaz on Mar 16, 2005 6:37:58 GMT
Something doesn't pan out .. A shuttle/rocket launch the 'g' builds up gradually ...to launch out of a large gun ..the G would bang in AT EACH section that fires ..ie each charge to build the speed for the cylinder (super gun/german gun V3 operation were there is a charge at various sections along the gun) infact the G/speed would bang in STRIGHT AWAY as soon as the button was pressed for launch .... The occupants simply would not survive the RAPID build up of G force. Well, it depends a lot on how you use the gun and how it's configured. With a conventional gun (see my quick and dirty sketch below), you can think of it as a piston (the bullet) and a really long cylinder (as in engine cylinder, not Martian cylinder). When the charge fires, the gasses press against the bottom of the bullet with so many pounds per square inch, applied over so many square inches of area of the base of the bullet, which creates the force that pushes the bullet down the barrel. As the bullet moves, the volume of space in the barrel behind it increases, so the pressure drops until (if the gun is well designed) it drops to ambient at the muzzle. You can see what this does in the graph to the right. There's a sharp initial spike in acceleration as the gasses reach maximum pressure, which then drops off as the gasses expand and the pressure behind the bullet drops as it speeds up. The area enclosed under the curve is the total impulse applied to the bullet. In a staged gun, the charges are spread down the length of the gun: So the first charges build up a lower pressure behind the bullet than a conventional gun, then each subsequent set of charges simply maintains that pressure by adding gas to the system. What you get is the curve to the right of the staged gun: A lower, but relatively constant, pressure that keeps the bullet accelerating at a lower, but also constant, value for the full length of the barrel. If I'd drawn the graphs right, there would be the same total area under each curve, indicating the same total impulse. It's like flattening out the curve in the conventional gun. You don't have to endure the huge initial spike in G's, but you get the same total push. I don't see how you could build a conventional gun that could launch the vehicle to space without such a huge initial spike in G's that it wouldn't crush the Martians. A staged gun, however, could keep the G's at a constant lower level, and that might work with the right configuration of gun. Lancer covered all the rest, as far as reasons for using a gun, etc. And he's right, if you have enough 'side charges', the ride would be fairly smooth. Using a staged gun, the barrel has to withstand a much lower maximum pressure, so it can have a thinner wall and breach, which solves some of the construction problems, too.
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Post by Lensman on Mar 24, 2005 3:34:30 GMT
I'm just getting over being sick Is there a worldwide epidemic? I have been down with a sinus infection, in fact 3 out of 4 of my regular Sunday FRPG players were out sick. I'll try to post some preliminary cylinder specs as a starting point tomorrow. You're not going to believe how heavy that cylinder is! Actually I will! I've already done some preliminary calculations: Assuming a cylinder 90 ft diameter with a length 2.5 times the width, and ignoring the ends, and converting to metric for convenience I get: 90 ft x 3.14159 x 225 ft x 2 ft = 127,234.395 cubic feet = 3,602.88 cubic meters water = 1000 kg/cubic meter = 1 kiloton/cubic meter balsa wood 170 kg/cubic meter = 612.49 kilotons beryllium density 1.8477 = 6657.04 kilotons aluminum density 2.643 = 9522.41 kilotons cold-drawn steel density 7.83 = 28,210.55 kilotons Of course, those are just numbers. With nothing to compare them to, they're meaningless, at least to me. So let's compare the weight of the Apollo/Saturn V rocket, loaded with fuel: 6.1 million lbs =~ 2767 kilotons Whoa! Yeah, that cylinder weighs JUST A BIT! Of course we don't know what the "yellow-white" metal was the cylinder was composed of, but even assuming it's an arbitrarily light metal like beryllium, that's still over twice the weight of the Apollo/Saturn V rocket, and actually it's more 'cuz I left off the rear end cap, plus that's just the weight of the empty cylinder without anything inside. And I think a weight equal to aluminium would be a lot more realistic, and that weighs about 50% more. Of course we see with modern composite materials it's possible the cylinder might weigh a lot less, but I'm assuming that when Wells said the cylinder was made of metal, he meant exactly that.
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Post by Lensman on Mar 24, 2005 3:40:02 GMT
wasn't the Orion 'powered' by detonating nuclear bombs behind it to push it forward The actual proposal for the Orion spacecraft did indeed used nuclear bombs for thrust, shot out behind a VERY large pusher plate mounted on a VERY large shock absorber. See the Niven/Pournelle novel Footfall for more details.
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Post by Lensman on Mar 24, 2005 4:02:34 GMT
I can think of simpler ways to launch an invasion force...the martys certainly made life difficult for themselves I have just received a telepathic communication from Megolumpdoo, a Martian, which I am relaying per his request: You humans are very silly using your vastly inefficient rockets. You certainly do make things difficult for yourselves. Your Apollo/Saturn V rocket used fully half its fuel just lifting itself its own height off the ground! That was the culmination of what your scientists called the MISS system (Man In Space Soonest). Putting a man in a capsule atop a missile was a quick and dirty solution to getting into space-- certainly not the best or most efficient! Now the giant space gun is of course a much more efficient use of resources. You only have to build a single one, and you can use it to launch a capsule every single day. After the gun is constructed, the only major cost, aside from constructing the capsule and its contents, are the explosive charges, and the trouble and expense of cleaning the barrel between each use. More importantly to our "astronauts", it is a much more *reliable* system. How many of your spacecraft have you lost to accident? Our very strongly built capsules and completely reliable launch system are much safer than your trouble-ridden, fragile, extremely explosive rockets! I understand you have been experimenting with your own space gun, using an evacuated barrel and placing it on a mountaintop. Clearly you realize the advantage of such a system. Perhaps someday your technology will advance enough that you can actually construct one. Until then, you poor humans have our sympathies.
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Post by Lensman on Mar 24, 2005 21:26:59 GMT
Also just what the hell type of charge actually started the cylinder off ...jeez it had to be HUGE, bearing in mind the breech of the gun was buried ...what the heck happened to the recoil and exhaust gas ...wouldn't s simply blow the entire gun/breech to bits....How much explosive would that have taken? ?? In Verne's From the Earth to the Moon, the Space Gun used 400,000 lbs of guncotton, but the capsule to be fired was much smaller than the 90 ft diameter Wells specified. Yes, it will take a very great amount of explosive. Presumably the Martians will use something of less bulk than guncotton; C-5 plastique explosive or something similar. And aside from the bulk, it really doesn't matter what you use for the explosive. The point is that for each charge, you use enough to give some acceleration to the capsule, but not enough to harm the occupants. That's one of the advantages of using multiple charges. You use as many separate charges as you need, spaced along the length of the very long barrel (thousands of feet long, possibly over a mile) to provide an acceleration gradual enough for the occupants to be safely propelled to the final velocity. Your comment about "exhaust gas" indicates you don't understand the principle of a gun. Any loss of gas from the breech results in inefficiency. You *want* all of the gas to be contained; it is the expanding gas that propells the projectile. Of course many modern guns do vent some of the gas to perform work in re-cocking the gun and/or ejecting the shell case, but older muzzle-loading cannons did not, nor will our space gun. If firing the gun blows off the breech, then clearly you have not designed the gun strongly enough. Verne's space gun was a muzzle loader. I imagine the Martians' gun is a breech-loader, as that would be easier to load, and make it much easier to clean out the barrel between shots. There's also the question of whether they could aim the gun or not. Certainly for such a large gun it's much easier to make it stationary, in fact bury it in the ground as Verne's Space Gun was, but perhaps the Martians want to be able to aim the gun. I suggest they did not, and the landings of the capsules in various parts of England were random variance, but others have suggested the Martains' aim was precise enough to place capsules in specific spots, in which case it's necessary for the gun to be placed in some sort of moveable framework.
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Xav
Full Member
Rules are for the obeyance of Fools and the guidance of wise Men
Posts: 119
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Post by Xav on Mar 28, 2005 2:41:59 GMT
Seems to me very obvious that the Martians could no more solve the Three Body Problem than we could and that mid course corrections would have to be made. At launch the gun would have to be a sort of explosive rail gun (as explained in previous posts) so that the g-force of the acceleration would not exceed the physical limitations of the crew. On approaching Earth, the Pilot would put the cylinder into a series of "breaking ellipses"; just grazing the Earths atmosphere in smaller ellipses until the target (SE England) was acquired and this difficult hard landing achieved. I think that there would have been a long scar in the Earth as a very heavy (several thousand tons...dont have me calculator)cylinder grazed the surface of the SE UK and finally came to rest in the middle of a lot of sand and gorse bushes. There is no question of it dropping down at 25,000 mph into the ground.
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Post by Lensman on Mar 29, 2005 4:42:40 GMT
Seems to me very obvious that the Martians could no more solve the Three Body Problem than we could and that mid course corrections would have to be made. I could be wrong, but my understanding is that the inaccuracies which necessitate mid-course corrections aren't mistakes in the math, but rather the inability to precisely control the propulsion system. If you're using a rocket, then the rocket may veer of course just a bit, and the cutoff of the rockets may be a bit ragged, etc. Small errors creep in. Using a giant cannon, there would likewise be some variation on exactly how fast the exploding gasses expanded, plus the friction of the cylinder rubbing the inside of the barrel, first on one side then the other, would introduce random forces. Wells wrote in a time before scientists understood the limits imposed by quantum uncertainty and "chaos" mathematics. Back in his day, there was a view of the universe as a giant clockwork mechanism, and a view that improvements in technology would produce improvements in accuracy without limit. On approaching Earth, the Pilot would put the cylinder into a series of "breaking ellipses"; just grazing the Earths atmosphere in smaller ellipses until the target (SE England) was acquired and this difficult hard landing achieved. I think that there would have been a long scar in the Earth as a very heavy (several thousand tons...dont have me calculator)cylinder grazed the surface of the SE UK and finally came to rest in the middle of a lot of sand and gorse bushes. There is no question of it dropping down at 25,000 mph into the ground. I think everyone contributing to this thread agrees the Martians shed most of their velocity before the final landing. We can't agree on the method they used to do so. Skidding in for a long slide upon landing has made spectacular sequences in several movies, but I don't think it's realistic to think anyone could predict that actually happening. First you'd have to control the cylinder's descent precisely enough to get a trajectory which barely grazed the ground-- this would require a degree of control impossible without propulsion, and if you have that you can use retro braking. And even if you could come in at the precise angle to just graze the ground, chances are the cylinder would hit something solid before it slid to a stop. Anyway, Wells never described them sliding in to a stop. He described meteoric impacts.
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Xav
Full Member
Rules are for the obeyance of Fools and the guidance of wise Men
Posts: 119
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Post by Xav on Mar 30, 2005 1:49:43 GMT
Unfortunately, McTodd, ultimately, you are quite right--- Wells described these things as arriving at god-knows-how-many-miles/second and both the vehicle and its crew surviving what can only be described as a extreme crash landing. I just cannot accept this. To survive this kind of landing would require a knowledge of inertia that is at odds with the rest of the Martians technology.
By this, I mean that if current thinking is correct inertia is the result of a body interacting with something called a Zero Point Field. An object accelerating through a ZPF causes a force to be applied to the object that is proportional to the acceleration but acts opposite to the acceleration. The whole idea turns physics on its head, forcing us to reconsider the idea of mass. In the classic model, inertia is a property of matter, a resistance to acceleration that can be seen and felt but is impossible to explain.
In other words, properly understood, any object is essentially without mass, being just a collection of massless electric charges. These are acted on by the ZPF so the interaction gives the impression of mass. Bugger, I hope I am not being too pedantic here....
Being able to control such a field takes us way off into a whole lot of quantum physics, including gravity. If the Martians could survive an impact landing by the use of a controlled ZPF, their use of walking machines seems quite absurd as does the idea of a huge cannon also.
The Three Body Problem is essentially that it is impossible for an observer on one of the bodies to predict where the other two will be at any future epoch. This plus the variations, as you state, at the launch make a series of mid-course corrections important., indeed essential. I think that a huge lifting body (sort of half cones, aerodynamically smoothed---I am sure you know what I am talking about) plus retrorockets plus breaking ellipses would be sufficient for a reasonably smooth landing. But...as you said...the damn things came straight in.... I enjoyed the post, McTodd.....
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