Xav
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Rules are for the obeyance of Fools and the guidance of wise Men
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Post by Xav on Mar 30, 2005 2:03:23 GMT
As an addendum to the Cannon discussion...I was wondering that instead of the chambered model that has been proposed where charges are exploded behind the passing cylinder....what if there was one very large chamber in the breech that was simply a gas producer? Rather like a rocket motor that would fire at fairly low thrust to get the cylinder moving, then throttled open (again controlled) to accelerate the cylinder up to departing velocity. This would avoid the huge suddenly applied loads to the gun barrel, the cylinder and its crew as the charges exploded behind it. The fuel? Hydrogen and oxygen....steam....air....anything that could be heated and expanded in the breech motor. I would favour the hydrogen/oxygen model so as to be consistent with the story. Just a thought.
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Post by Lensman on Mar 30, 2005 7:15:00 GMT
That might work. I think the HARP gun used highly compressed gas, perhaps just pressurized air. The problem is that the farther from the breech the cylinder gets, the higher the pressure has to be for any pressure wave to "catch up" to the cylinder, both because of the distance and because the cylinder is traveling faster the farther it gets. I don't know how to figure out if your proposal would actually work or not.
But I think Christopher Priest had a better idea in The Space Machine. Put in a plug of ice behind the cylinder, and use a heat ray in the breech to heat the ice into expanding gas. If you can maintain the heating all the way, it provides even acceleration.
Unfortunately, Wells describes the gas explosion as "chiefly hydrogen" and I don't know how you could achieve that with ice. Frozen hydrogen would be so close to absolute zero it would be hard to maintain in solid form. But then, the same problem arises with use of conventional explosives... it doesn't result in a lot of hydrogen released.
I spoze you could pump in highly compressed hydrogen and oxygen at the various stages along the barrel and ignite it; that might give the desired result. Or perhaps you could figure out a way to use the heat ray to heat the gas, and just use ice to protect the cylinder, without the mass of ice contributing much to the explosive gasses.
No doubt Topaz can give us a better idea of what will work and what won't... if he ever returns to this thread.
(Hint! Hint!)
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Xav
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Rules are for the obeyance of Fools and the guidance of wise Men
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Post by Xav on Mar 30, 2005 21:49:34 GMT
I do apologise, Lensman....You are not McTodd
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Post by mctoddridesagain on Mar 30, 2005 22:28:56 GMT
No, he isn't...
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Post by Lensman on Mar 30, 2005 23:37:07 GMT
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. Well I admit during this discussion my idea of atmospheric braking has been made out to be highly questionable. I hate to fall back on some super-science method of the Martians reducing their velocity, but I admit at the moment I can't come up with a better solution. If we fall back on super-science, there are many possibilities: Star Trek's inertial dampeners; the Kzinti gravity polarizer from Niven's "Known Space" series; partial inertial reduction, as in E.E. "Doc" Smith's Triplanetary (clearly not full inertialessness, as used later in the "Lensman" series). I haven't heard of the effect you're referring to, but assume it would have the result of partial inertialessness. Of course, Topaz and Lancer maintain they used retro-rockets. My opinion is that if they used those, they could have achieved a soft landing. To remain true to the book, whatever the Martians used needs to have been able to shed most, but not all, of their velocity. Something like a gravity polarizer would fit the bill, if its efficiency is proportionate to the difference in velocities (between the spacecraft and the planet), so that the polarizer could shed high velocity with ease, but couldn't shed those last few hundred MPH of velocity, resulting in a "hard" landing. Another possibility is use of the heat ray as a propulsive device. The advantage is that it is used to heat the air, and the expanding air provides propulsion, so the spacecraft doesn't need to carry rocket fuel. One might theorize this would work only after the cylinder entered the atmosphere, and there simply was not enough *time* for it to completely shed the velocity. Or-- a better idea-- perhaps such a propulsive device works well only with a very high volume of incoming air-- like a ramjet-- so when its speed fell below Mach 1, it no longer was able to decelerate the capsule effectively. Hey, I like that idea! It doesn't involve any "new tech" that the Martians must have.
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Xav
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Rules are for the obeyance of Fools and the guidance of wise Men
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Post by Xav on Apr 4, 2005 0:29:18 GMT
Not quite sure where you get your figures from, Topaz, but I have done a re-calc because I had the feeling the values were too low. The volume of a cylinder is the cross-sectional-area (CSA) multiplied by the length. Assume Length is 225 feet. Material is titanium at 280 lbs/cuft
Vol = pi x L (R^2 - r^2)
= pi x225(45^2 - 43^2)
leaving out the intermediate steps....and adding on the weight of 6 foot thick ends.... Weight = 25,000 tons (empty)
The Payload would be crew, life support, machinery.
The volume of the cylinder is...hmmmm....approx.... 1.3 million cuft.
I would guess this is sufficient for three FM's, a Handling Machine, extra materials, 5 crew aand half a dozen snacks on the way.
Will someone check my maths, please?
Lensman, nothing wrong with the idea of atmospheric braking...my suggestion of 'braking ellipses' is just that where the cylinder might do a half dozen orbits, plunging into the atmosphere deeper on each pass and shedding velocity. Definitely buy the idea of an ablative shield.
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Post by Lensman on Apr 5, 2005 5:02:45 GMT
adding on the weight of 6 foot thick ends.... Why 6 foot thick ends? The rear end which screwed off was said to be about 2 feet thick. From this I exropolated that the walls of the cylinder are 2 feet thick, altho of course that's an assumption. This is quibbling, of course... the weight of the end cap is only a small fraction of the whole. BTW-- Those figures (or more precisely, estimates) for the weight of the cylinder were my figures. Topaz never go around to posting his. HINT! HINT!! HINT!!! I just figured the volume as a flat sheet, as tho the cylinder had been cut lengthwise and flattened out. Not quite as precise as the way you did it, but I doubt the difference is significant. Not sure why you added a front cap. I figured if one were to cut "orange peel" sections out of the front third of the cylinder and weld them together into a conical nose, it would be roughly the same as cutting off half the length of the front third (which is why I put the length at 2.5 times the width, instead of 3 times). Of course there's nothing to say the length from nose to tail actually was 3 times the diameter; it's all guesswork so far as I'm concerned.
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Xav
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Rules are for the obeyance of Fools and the guidance of wise Men
Posts: 119
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Post by Xav on Apr 7, 2005 22:47:03 GMT
Six foot thick endcaps were my rough estimate of an equivalent to a cone shaped body fore and aft, thats all it was. And as far as the ends being a small fraction of the total...this masses about 9,000 tons. But, as you say, this is quibbling. The things were massive. I would certainly go along with the idea of some sort of ablative covering, both to resist the heat of the gun firing and the rapid transit through the Martian atmosphere and the eventual series of braking ellipses that I imagine took place within Earths environment. How the Martians withstood the shock of landing, even if the vehicle was a lifting body and could sort of 'fly', is anyones guess. I am imagining some sort of inertia damper, I think.
There was some really interesting discussion elsewhere concerning the dates of launch, transit time across space etc etc...and the point was raised, although only obliquely, concerning the number of cylinders fired. It seems ten only when the time before and after Opposition would have allowed about 80...a far more realistic number, I would have thought. Fifty of the invaders really had no chance at all, if they were going to killed off at the rate of, what, four every couple of weeks? Well, of course, such a rate may not have been sustained, but it does give a bit of an indication. Now, 400 warriors with all the gear, would certainly be quite a different ball game and would have been an enormous problem for the armies of Europe, if that was the next step.
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Post by Topaz on Apr 9, 2005 21:50:50 GMT
BTW-- Those figures (or more precisely, estimates) for the weight of the cylinder were my figures. Topaz never go around to posting his. HINT! HINT!! HINT!!! Yes, I've been a slacker. But at least I'm a slacker with a good excuse: I've just returned from the hospital. My illness returned, and turned out to be a bit more than I'd bargained for: pancreatitis. Nasty thing, and I don't recommend it! Early the week before last they removed my gall bladder as a result. I think the doctor needed to get a new Mercedes. I'm home now and much, much better, so I promise (promise!) to get back into this discussion in-full shortly. I'll try to post my cylinder calcs today (today!) for all the world to pick apart. Glad to be back! Topaz
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Post by Spirit of Man on Apr 10, 2005 1:28:54 GMT
Heres my "opinion" and don’t get all sciency on me , after all it was a book of fiction.........but I believe that the cylinder was controlled by the same method that was used to make the flying machines fly........some sort of suspension field. So the cannon on mars could apply the power enough to allow the cylinder to escape the martian gravity, then the cylinder would accelerate in space (for speed of travel) and at a certain point start slowing down, picking its point of entry into earths atmosphere with its landing site already plotted. Im not suggesting that this field would allow for alot of manoeuvrability, but would allow the speed and direction changes required........this field could then be generated within the cylinder as a form im inertial dampening, effectively quashing the effects of the impact. Sorry guys......no maths.......no scientific theory.......jus some fiction ;D
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Post by Lensman on Apr 10, 2005 10:53:41 GMT
My illness returned, and turned out to be a bit more than I'd bargained for: pancreatitis. Nasty thing, and I don't recommend it! Early the week before last they removed my gall bladder as a result. Oh my. That means a change of diet for life. Sorry to hear about your health problems, Topaz. Be well!
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Post by Topaz on Apr 10, 2005 15:57:10 GMT
Yeah, I think I'll have to swear off blondes. Thanks. Doing much, much better now!
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Post by EvilNerfherder on Apr 10, 2005 17:44:08 GMT
Good to see you back and better, Topaz.
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