The parabola is an approximation; the equation of motion that defines a parabola assumes that all the gravitational force is always in the same direction (ie, horiz velocity constant, vertical velocity = V0 - kt^2) But in reality, the gravity vector points at the center of the earth, so changes in direction as the shell moves, and that's not a parabola any more.
It's an ellipse because, except for the minor detail of crashing into the earth, if the shell were allowed to follow its natural path, it would loop around the center of the earth and arrive back at the gun. That's an orbit, not a parabola.
The path is one curve or it's the other. It's math, not pedantry. For a really huge Big Bertha sort of shell, it will matter enough to matter.
Yes, but the issue is: what's the path before it crashes? It's an ellipse, but approximated pretty well by a parabola, for most practical applications.
In the game Homeworld, most of the ships are equipped with some sort of bullet weapon (the documentation calls it a "mass driver", presumably something like a railgun). You can watch them fly to the target like tracer rounds. Lots of leading the target, and evasive maneuvers (quite costly on fuel, or so you would think) for the little buggers.
No mention appears to be made of recoil (except on the turret mounted cannons), but targets under heavy fire do tend to be pushed back.
Movement isn't relative either, all ships have an absolute speed with respect to the map. Shame...
Tim
-- Deep Fryer: A very philosophical monk. Website @
If you're orbiting in the "opposite direction" of your targets, a gun's muzzle velocity doesn't add much to the already extremely high differential velocity between your platform and the target (although it might be quite useful if you need to get a projectile to a location that's some perpendicular distance from your orbit). With the high differential speed involved, a tiny spring pushing out a single BB could kill almost any target, assuming the BB hit it.
This type of stuff was all already pretty-thoroughly designed by the early 1980s.
[Then the Clintonistas killed most of the SDI programs, around the same time that they allegedly gave the Chinese military a) the "fix" for their ICBMs' stage-separation problem, b) Loral Corp's precision guidance system that "upped" their accuracy into the silo-killing range, and c) the design for "the bus", i.e. the mechanism that ejects each of the re-entry vehicles "just right", the three of which together solved basically all of China's remaining nuclear strike capability problems, allegedly. That was also at about the same time that we sent an aircraft carrier to bluster about the Chinese launching test-firings of missiles directly over (Taiwan, was it?), at which time a Chinese spokesman publicly scolded the U.S. and casually asked if we'd like to have a nuclear missile strike L.A. (presumably if we didn't start minding our own business instead of "interfering"). At the time, Loral Corp's CEO was allegedly Bill's largest "legal" campaign contributor, and the Chinese military was allegedly his largest illegal campaign contributor. I might assume that Monica was the main PR diversion-tactic, when needed.]
Anyway, you can think about the BB, and its "rather large" kinetic energy under the right conditions of engagement. And you can think about clouds of BBs, as someone mentioned. You can think about the trade-offs between numbers and sizes of platforms and their weapons, versus costs of same, versus how many decoys you have to kill to be sure that no live nukes get through, and on and on. And you may arrive at a solution that's similar to the "Brilliant Pebbles" concept.
Also, sensors and guidance will not be an afterthought, as you seemed to imply in a later post. i.e. You won't want to spray projectiles from a machine gun and just wait to see if you get a hit.
Actually, it all boils down to costs. e.g. If we had a small number of very expensive but very good orbiting killers, then a _large- enough_ number of decoys _could_ defeat them, in the sense that an actual warhead could practically be guaranteed to get through, if enough decoys were also used. (A smaller number of platforms is also easier for the other side to try to take out.) But, if we can have enough orbiting killers, then we can also kill all of the decoys. So, who will "win"? Well, if we can make and deploy our killers for a way lower price than they can make and deploy even decoys, then we probably win (that part of the game, at least). So, again, one potential solution might tend toward something like the "Brilliant Pebbles" concept.
The limit of what? There is a simple energy relationship which is negative for ellipse, 0 for parabola, and positive for hyperbola commonly referred to in orbital mechanics. I can derive it here for you, if you wish. Also, in geometry, you can view the relationship of ellipse, parabola, and hyberbola, as a double cone (same shape, with points touching) sliced by a plane at various angles relative to the double cone perspective-edge.
See:
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Yes. Can you develop the simple energy equation that explains why?
But an artillery shell falls along a section of an ellipse, with the earth's center one of the foci. The concept of parabolic shape comes only from viewing gravity as always in parallel rays "downward." But on a sphere such as that approximated by the Earth, these rays are not parallel, but central. That forces the shape into an ellipse. It just turns out that for shorter trajectories, a parabola is sufficiently close for many purposes.
Well, I wouldn't say "last point of acceleration." An orbit repeats its path, leaving out relativity and other influences. But the term acceleration may be too easily misunderstood to suggest that if an object is under artificial (outside of that caused by gravity) acceleration that such a point must be included. It doesn't have to be and probably won't be, if the acceleration proceeds beyond that one point.
If this is meant as evidence to me that a bullet does not travel in an ellipse, you are dead wrong about it.
Yeah, it seems you are arguing this way. You are wrong about it.
I'm guessing a nuke blast in space creates a sudden burst of energy which propagates at high speed. Kinda like instant heat rushing by. . (mini sun) So..a nuke cooks a satellite? It would vaporize, melt or burn it depending on the distance.
I don't see a collision producing enough delta-v to deorbit the whole sat; most of it should have gone into random variations of the original satellite's orbit to make NORAD's job just that much more difficult. I don't know of any reports of debris re-entering.
That as well, but I don't think it'll escalate to the rest of the world having to play the MAD game with China; they're much more level- headed than the USSR was.
Wrong, Dimbulb. When they're pulled in there is no knowing what the orbit is until it's measured. Some are obviously hyperbolic, some obviously elliptical. However, some are too close to call and are listed as parabolic.
Have you ever heard of escape velocity? Good, now go away.
The ingredients on a can of smokeless powder I have are: Nitrocellulose, nitroglycerine, diphenylamine, ethyl centralite, rosin, polyester. No proportions are given, but I'd guess that they are ordered by decreasing weights.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
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Matter cannot be created or destroyed, nor can it be returned without a
receipt.
Why haven't you bothered to argue based on the physics?
--
Paul Hovnanian mailto:Paul@Hovnanian.com
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Steinbach's Guideline for Systems Programming
Never test for an error condition you don't know how to
handle.
" snipped-for-privacy@bid.nes" wrote in news: snipped-for-privacy@e65g2000hsc.googlegroups.com:
even items at 500 mile orbits eventually decay and reenter. most low Earth orbit stuff reenters a lot sooner,due to atmospheric drag and gravity effects.
Then why are they devoting so much of their GNP to military? Building lots of new quiet subs,LOTS of ballistic missiles,all sorts of stuff.
Easy;they plan on confronting the US sometime in the near future.
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