Half a croissant, on a plate, with a sign in front of it saying '50c'
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Planetary Ring

The Moon had one in Starship Troopers
  [vote for,

Set up a series of electromagnetic catapult coils around the equator, thread a thin metal hoop through all of them, and spin it up to tension. Then expand the ring by spraying on new metal at the coils and accelerating it just beyond its elastic limits, and build towers under the coils to follow it upward.

Unlike a single space elevator, this project offers easier space launches from day one, (Small spaceplanes can achieve escape velocity by using magnetic grapples to borrow momentum from the ring) and when it reaches geostationary orbit we can adjust its spin to 1G and use the metal to build facilities, ships, free-floating arcologies and damn great gun turrets.

Mharr, Aug 18 2001


       I usually get pretty excited about "damn great gun turrets". But let's keep them on terra firma where they'll be most beneficial.
The Military, Aug 18 2001

       Millions of square miles of solar cells, uninterrupted by weather. Or an updated version of an old, old idea I had as a kid...MHD generators driven by solar power, using the extreme temperature gradient between sunlight and shadow <Original idea was water wheels. Hey, I was ten!>.   

       That's where to get the power. As to the idea, I don't know if I really understand it. What he seems to be saying is spin a ring large enough to completely encircle the Moon using linear accelerators quickly enough that it stretches, adding more metal on the fly to make it larger still, and have 'spaceplanes' lifted up towers to grab onto the ring and be instantly yanked to orbital speed all at once, which sounds like an absolutely terrifying prospect, to me.   

       Better might be something like an upside down car on top of the plane, with wheels and electromagnets to grip to the ring. <Whoo, boy, is this ever gonna be half-baked...I blame lack of sleep, being up waay to early, and Too Much Coffee on an empty stomach.>   

       Put the wheels in neutral, lift the vehicle to touch the ring <elevator on the launch pad, or whatever>. Hold the vehicle in place while the wheels get up to speed, then flip on the electromagnets and release the cradle. Theory being the magnets will supply enough grip to keep the plane attached to the ring. Slowly brake the wheels so the plane is dragged along faster and faster, until the wheels are fully stopped and the plane has matched the speed of the ring, held in place by the magnets. Through some process I haven't determined, possibly 'driving', move the plane to the other side of the ring, and release the magnets and launch with the full velocity of the spinning ring.   

       Problems: Building the ring that large. Spinning it with linear accelerators, as I don't think they'll work on a continuous length. <They work by turning on a magnet ahead of the item, pulling it forward, then repeating>. Switching sides on the ring. Multiple vehicles at once <Possibly something similar to railroad tracks to avoid collisions?>. Having to build the ring to withstand moving at 5369mph, the Moon's escape velocity. Having to build TIRES that can do this. I'd want redundant power supplies for each ring, because if all of them failed at once, it's going to crash and make one hell of a mess. Having to cut through mountains and fill valleys all around the Moon to get a level track. <Alternatively, build it somewhat wider and put the lifts on top of the mountains. This would require the accelerator rings to be on Tall Ass towers.>
StarChaser, Aug 18 2001

       Re: the problems: The industrial capacity to build really big stuff is automatically a problem for this class of project. Linear accelerators should work provided the ring has alternating bands of more and less reactive metal. Physically touching the ring isn't really in the concept, just using electromagnets to gain traction at a distance and be pulled along. Escape velocity isn't a necessity, as even a small externally powered boost will dramatically reduce the need for fuel mass on a spacecraft, and the plan is to slightly exceed its tolerance so that it stretches in any case. It shouldn't need any power to stay up if it's spinning fast enough to remain circular under tension, just the occasional nudge to keep it centered. The imperfect circularity of planets in general does make it more expensive at first, but assuming we intend to build a ring at some stage, this still seems cheaper than starting in orbit, and more useful whilst still under construction.
Mharr, May 10 2002

       Actually, isn't there a physics issue, in that a connected ring can't really form a stable orbit? Something about it having a constant linear velocity along the ring, but if it gets a bit closer to the world it experiences stronger gravitational force and tends to fall even lower?
TomRC, Aug 27 2002

       A building a ring is possible but building towers to push it in to geostationary orbit isn’t. I could see a ring being constructed by building thousands of space elevators. Each would extend far enough past geostationary orbit that centripatal forces generate about a half G. At the end of the elevator a space station is built in essence it would be a hanging city. Then the cities would be connected using the same material as the elevators are made from. Once connected the cities could then slowly over generations grow along the connectors until they meet.
duroncrush, Jan 06 2004


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