McAnally's (The Community Pub) > Author Craft
an engineering problem which I need to solve for a story
knnn:
--- Quote from: lt_murgen on July 10, 2012, 12:48:36 PM ---The designers of the “bullet” realized they needed to be able to control the center of mass in-flight. To do that , they designed a simple guidance mechanism. It is a pressurized, fluid filled series of tubes criss-crossing through an open sphere. Syspended in the fluid are small ball bearings. A gyroscope/magnet system can make the ball baerings move/clump about the device, altering the center of mass enough to make small adjustments.
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Remember that no matter what you do, in a closed system the center of mass should will still end up moving in the exact same trajectory.
Thus, unless you are positing secondary explosions (blowing off chunks of the bullet), or thrusters (fast moving gas particles in a perpendicular direction), "moving around the center of mass" inside the shell will not really help change the course of the bullet.
Figging Mint:
--- Quote from: the neurovore of Zur-En-Aargh on July 10, 2012, 03:19:30 AM ---Basically, the existence of the hidden object has to not be deducible from the shell's design, by someone who has access to most of the records and many of the people involved, or from examination of the impact site.
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Give it a logical overt reason for existence? I mean if you're delivering resources as disparate as uranium and copper at the same time it would be somewhat logical to attempt to keep /some/ heavier resources closer to the surface, so it would be natural to attempt to randomize the energy of those heavier resources? One way to do the randomizing might be to have collisions amongst several heavy-resource bodies within the bullet? Essentially, the bullet turns into a dead-blow hammer?
Figging Mint:
--- Quote from: the neurovore of Zur-En-Aargh on July 10, 2012, 03:19:30 AM ---They don't really scale well to a hundred-thousand-tonne shell by my back of the envelope calculations. (Also, the folks making this have a certain weakness for the grandiose.)
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Ah, 'k. Volume vs. area bites us on the bottom /again/.
Quantus:
With regards to the Bullet Shape, that is only actually a benefit is you expect to impart an axial spin on the slug, as the rifling inside a gun barrel would do. It doesnt sound like you expect to have that kind of control at the launch (though it could be theoretically possible with well timed magnets or some such).
Without that spin the bullet will inevitably start to tumble, which will hurt accuracy quite a bit even in space (rotating systems can skew the trajectory, not unlike a curve ball). Without that spin, a sphere is far more efficient. Specifically, a sphere with golf-ball style divets. Believe it or not, the divets actually decrease that drag forces from the atmosphere, which increases range. In this case that would decrease the force required to make orbit.
the neurovore of Zur-En-Aargh:
--- Quote from: Quantus on July 10, 2012, 04:46:17 PM ---With regards to the Bullet Shape, that is only actually a benefit is you expect to impart an axial spin on the slug, as the rifling inside a gun barrel would do. It doesnt sound like you expect to have that kind of control at the launch (though it could be theoretically possible with well timed magnets or some such).
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I'd been thinking roughly bullet shaped rather than sphere because of wanting fairly even impetus across the bottom of the thing for the launch - it's kind of a limit case of http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 , really.
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