Monday, April 02

Geek

A Choice Of Catastrophes

One way to build a large space habitat with real-world materials is to put a large mass on the inside and live on the outside.  Use the mass, instead of the rotation of the habitat, to generate gravity.

Let's try doing this with Jupiter.

Jupiter has a diameter of 143,000km, and a "surface" gravity of about 2.4g.  So a habitat with a diameter of about 340,000km will experience a gravity of 1g.  With a circumference of over 1,000,000km and a width of 10,000km (preserving at least 93% of Jupiter visible to Earth-bound astronomers), it would have a surface area equal to 20 Earths.

We spin the habitat once every 24 hours to give us day and night.  That works out to about 0.1g of outward acceleration, so we only feel 0.9g.

The problem with this is that the habitat will be under massive compression stress.  Just as an equally large habitat with 0.9g of centripetal acceleration would fly apart instantly, this habitat would instantly collapse and crash into Jupiter.

However, while there are no energy-efficient ways to dynamically reduce tension, there are ways to reduce compression.  What we do is create a second structure just inside the first, and rotate it much faster, so as to balance the force of gravity on the structure itself.*  Gravity still effects people and things on the outer surface of the habitat, keeping them in place, but the habitat is dynamically stable - at least structurally.

The problems with such a structure are similar to Niven's Ringworld, with one or two added thrills.  First, it's not in orbit around Jupiter (though it is in orbit around the Sun), so that if it drifts off course relative to the planet it will keep right on going, or even accelerate.  If it is pushed towards Jupiter vertically, it will accelerate into the planet, which would destroy the habitat and kill everyone on it.

If, on the other hand, it drifts away from Jupiter laterally, it won't collide with the planet, but the loss of gravity will cause the atmosphere, people, pets, trees and so on to drift off into space and asphyxiate.  Well, it would, except that the inner ring, no longer bound by said gravity, would tear itself apart and the main structure along with it, killing the people, pets, trees etc instantly.

Oh, and I think Jupiter's radiation would be lethal.  And the structure would intersect the outer ring, so you might have to remove that.  And you would only get 4% of the sunlight intensity that Earth receives, so you'd either need a mirror 25x the size of the habitat to light things up, or some really warm underwear.

Apart from that, though, it's great.


* You'd need some pretty fancy bearings, but that's a mere engineering detail.

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