SH Comments
Reged: Feb 16 2004
Posts: 1056
|
|
This thread is for comments about Megastructures, by Paul Lucas
|
FredKiesche
New user
Reged: Feb 20 2007
Posts: 1
|
|
A couple of other things to add:
J.D. Bernal: The World, The Flesh and The Devil. Despite the title, it is a non-fiction book about (at the time it was written) possible futures. Bernal came up with the "Bernal Sphere" which was adopted for the O'Neil colonies.
Olaf Stapledon: The Star Maker. Inspired by Bernal, Stapledon had mobile spherical colonies in this classic work.
George Zebrowski: Various works, but most especially MacroLife. Recently republished by Pyr Books. The term "macro life" was developed in the 1960's (Dandridge Cole), but the works it appeared in are sadly OOP and I've never been able to track them down.
Gregory Benford: The various Galactic Center novels. Benford had some very large structures in these books.
Gregory Benford and George Zebrowski: SkyLife. An anthology about colonies, STL generation ships and more. Good mix of fiction and non-fiction.
Larry Niven was (with Benford) working on a book called "Wok World". Take a Dyson Sphere and only build half. Don't know the status.
Fred Kiesche
|
Brian Dunbar
New user
Reged: Mar 05 2007
Posts: 1
|
|
<i>Basically, a megastructure is defined as any single artifact that challenges human preconceptions of size.</i>
It is interesting that the definition of a megastructure will change over time.
The Brooklyn Bridge was a megastructure when complete, now it's 'just' another bridge. We might expect a space elevator to be the same.
Brian Dunbar
LiftPort
|
Bob Munck
New user
Reged: Mar 07 2007
Posts: 2
|
|
Quote:
A solid halo with an orbital altitude of 22,300 miles and a cross section of one square kilometer ... If spinning at the same rate as the planet below it would have a very modest gravity along its outermost surface, about 1/20th of a g.
No, sorry, centrifugal force and the Earth's gravity are almost exactly in balance there. Both are about 0.023 g, in opposite directions. You have to get up to almost 100,000 km (62,000 miles) on the space elevator before your effective gravity is 1/20th g. Or be about 17,000 km (10,000 miles) below geosynchronous, where gravity exceeds centrifugal force by 1/20th g.
|
Bob Munck
New user
Reged: Mar 07 2007
Posts: 2
|
|
Quote:
A solid halo with an orbital altitude of 22,300 miles and a cross section of one square kilometer ... 1/20th of a g.
As I said above, you can't get gravity that way. However, what you could do is make the halo a tube -- a torus -- and spin it around its circular axis. At first thought, that doesn't make sense; it's effectively turning inside-out continuously. However, this thing is immensely long: the equivalent of an inner-tube where the tube is 6" in diameter and the whole wheel is 10 miles in diameter. It's effectively a long, straight tube locally, easy to rotate around its long axis. If the tube is 10 km in diameter, the internal surface area is about 10 million square kilometers, approximately the area of the United states. You'd need it to be 600 km in diameter to have the same surface area as the Earth; that's probably too big.
However, You wouldn't actually do it that way. Much better to have a static outer shell providing the radiation protection and environment containment, and internal rotating cylinders each a few tens or hundreds of kilometers long. Different cylinders could spin at different rates, providing different gravity -- and of course they could be multi-level, with less gravity as you get closer to the axis.
Quote:
one of the main problems with engineering a solid halo is progressional instability. Attitude jets or other means of maintaining the immense artificial ring's position in the plane of its orbit would be necessary.
Maybe, but you don't need the altitude jets. Unlike Ringworld, the Halo can have spokes. That is, you can have a couple of dozen space elevators with Earth anchors below and counterweights above. Note that the structure is so big that it will have effectively zero compression or bending strength. You have to rely on high strengths in tension only, like carbon nanotubes. That's another reason to have multiple internal rotating cylinders: each space elevator has to go right through the middle of the tube and be attached to the main structure. The only way to do that is between rotating pieces.
|
plucas
New user
Reged: Nov 21 2006
Posts: 2
|
|
Bob;
You're right, I was off with my initial calculations of the gravity. That was a bad goof on my part. Apologies all around.
I do like your idea od a hollow planetary halo with inner rotating cylinders. However, attitude jets would still be needed in some cases. Halos do not necessarily have to be connected to the planet with Space Elevators, and if they're free-orbiting structures progressional instability will definitely be a factor. Also, those Halos attached to the planet with space elevators would not necessarily use those elevators for anything other than transporting material up an down. It might actually be more cost effective in the long run to build and maintain occasional-use atttitude jets than to build and maintain dozens of space elevators.
But still, very good idea idea. I may stea--er, "borrow" that one day for a story = )
--PL
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
