Hey Everyone,
So, I've finally reached the point where I'm going to be able to run a little EP, and I've been putting some work into developing some setting material for the game. I've decided to set it (at least initially) on Ceres, and I'm working on some of the basics for my version of the big Extropian colony there.
My basic idea: The founders of the colony used what basically amounts to mohole-digging tech to punch a hole through the regolith/ice crust, run a beanstalk through it, and then clamp a city to the underside of the crust. Water miners suck water to the surface through the city's infrastructure, freeze it at the base of the beanstalk, run the water ice up the stalk to waiting cargo ships in low orbit, and Bob's Your Uncle.
Here's my question. According to what I've read, the gravity on Ceres is about 3% of Earth standard, putting it squarely in the microgravity category. So, does it make more sense to orient "down" in the city as toward the asteroid's core, using that 3% along with magnetic boots and other such devices to approximate gravity, or is the natural spin of Ceres such that you could orient "down" as toward the asteroid's surface, counting on centrifugal force to "push" you in that direction, essentially fighting gravity to create gravity?
Any help is greatly appreciated; chances are good that you know more physics that I!
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Ceres Habitat -- Looking for some physics help
Mon, 2010-01-25 20:58
#1
JimJim
Ceres Habitat -- Looking for some physics help
Tue, 2010-01-26 05:14
#2
Iv
Re: Ceres Habitat -- Looking for some physics help
Ceres exists. It means that naturally the gravity force is superior to the centrifugal force. I doubt the ice crust could hold the weight of the ocean below if it was made to turn enough to produce a centrifugal gravity. So go for a regular low gravity.
Tue, 2010-01-26 23:41
#3
Arenamontanus
Re: Ceres Habitat -- Looking for some physics help
Ceres rotation period is 9.074170 hours. At a radius of 487.3 km, that produces a centrifugal acceleration of 4 pi r^2/T^2 = 0.018 m/s^2, or about 0.0018 G. So the local gravity is downward.
Note that you could get artificial gravity by making a sufficiently long beanstalk. However, it would need to be 270,000 km long, which sounds impractical. I'd rather put rotating habitats on it instead. Another fun idea (from Damien Broderick's "The White Abacus") is to make a circular underground railway, where maglev trains rush forward with enough speed to produce artificial gravity - they are essentially underground torus habitats.
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Wed, 2010-01-27 00:20
#4
JimJim
Re: Ceres Habitat -- Looking for some physics help
I've seen this mentioned somewhere before; I'm not entirely sure I get the concept. Is the habitat itself essentially a giant train, running along a track on the interior of the asteroid, or does an otherwise stationary settlement have a train track running along its circumference, producing the artigrav?
Wed, 2010-01-27 00:58
#5
Arenamontanus
Re: Ceres Habitat -- Looking for some physics help
Imagine a circular tunnel, something like a particle accelerator tunnel. If you run along the tunnel fast enough you are going to experience a centrifugal acceleration away from the centre of the circle. If you run really fast you will be running on the outer wall. Now lay tracks along the outer wall and instead run a train-habitat along the track. It could be a full circle of train carriages, or just a smaller train speeding along.
Getting into the train is of course the problem. Entrance would be from the tunnel roof, where the train would be rushing past below. You enter a little capsule, which is accelerated on roof tracks until it matches the train speed and you can climb down to the train.
Rotating habitats are always tricky to get into, since there is a need for linking a rotating and a non-rotating section. Torus and bolo habitats do it by having a hub with spoke elevators. No wonder so many transhumans opt to skip the whole problem and live in microgravity. Cheaper, fewer engineering issues, no moving parts that can break.
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Wed, 2010-01-27 01:59
#6
JimJim
Re: Ceres Habitat -- Looking for some physics help
Hmm ... good concept for a smaller hab, but I'm wondering if it would work for a city of 1 million+ (per the rulebook), transiting the interior of an asteroid the size of Argentina, made mostly of water.
The more I think on it, the more I concur with you that keeping it as a microgravity is probably the way to go. Though I'm wondering if four "bolo arcologies" mounted at the base of the beanstalk might be a possible alternative. You'd certainly have the centrifugal force pushing you out, but you'd still have that 3% pulling toward the planet, and I don't know if the former could cancel out the latter.
Wed, 2010-01-27 07:47
#7
Arenamontanus
Re: Ceres Habitat -- Looking for some physics help
No problem, actually. If you have a bolo arcology attached to the beanstalk by flexible fullerene cables and rotate it, it will tilt slightly due to the gravity field but still have a straight "vertical" as experienced from the inside. Think of how a bucket attached to a rope would swing around a pole in Earth's gravity field. On Ceres the tilt would be much smaller, of course.
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