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Spin that ring
Posted By: L. Tankersley ("Cap'n Carnage") <leland@tridsys.com>	Date: 12/20/99 5:12 p.m.
In Response To: Re: Internal orbits (Nathan) > I believe one of the Island Four posts (or several of them) have > a link to the precise definition of a halo orbit around a > Lagrange point, which is indeed stable. Something has to get the > ring spinning, though, to begin with ... as far as the > atmosphere, etc. is concerned. Anyone think about that yet? ;) Yep, and it's a bit worrisome. First, how fast does it need to spin? For the ring to provide 1g of artificial gravity due to rotation, it needs a rotational velocity of roughly 11,000 m/s, giving a rotational period of about an hour and a quarter. If you only require say 0.5g (which would make it easier for the marine to survive those leaps from high places) the required velocity drops to 8,000 m/s with a period of a bit under two hours. Assuming the ring isn't roofed over and there aren't magic force fields or gravity generators or whatever to keep the air in, you need high walls at the edges of the ring or the air will escape. I've forgotten what little I ever know about air pressure and how it varies with altitude (other than it goes down :P), but I know the walls need to extend pretty much into vacuum or air will spill out over time. Unless you've got a way to synthesize and replace air over the lifetime of the ring. ::shrug:: Figure a hundred miles high? I forget how high the Ringworld walls were. You might need them substantially higher under less than earth-normal gravity. Anyway, that's still a small fraction of the ring's diameter. It might obscure a lot of the view from the surface directly to either side of the ring, though. That brings up a side question: how wide is the ring? Well, let's assume it provides surface area roughly equal to that of the Earth. That's (very) roughly 133 million square miles - to provide this much area the ring would have to be about 4,000 miles wide (to go with its 31,000 mile "length"). The capacity of a thousand miles of air to obscure vision is pretty substantial - we shouldn't expect to see much of anything on the horizon. So the "rim wall" to borrow a phrase from Niven won't really affect visibility much, after all. As far as getting the ring spinning - you need energy and lots of it. If you built the ring from the material of a second moon, you would presumably have a lot of mass left over which you could use for reaction mass. Hope nobody's living on the planet or the other moon, though. Since the ring is located at the L1 point, maybe there's some interaction between the planet and moon that could be exploited to siphon off energy from the system and use it to spin the ring instead. Say if you charged the ring and made use of the magetic field of the planet somehow.....somebody, help me out here. [By the way, there's a nifty little java ringworld simulator at http://www.nas.nasa.gov/Services/Education/SpaceSettlement/teacher/materials/ringworld/ that lets you fiddle with ringworld parameters and see what ballistic trajectories look like on a ringworld.] L. Tankersley ("Cap'n Carnage")

Message Index

Human Space Capability	Napalm Loon	12/17/99 7:33 a.m.
...But where would they orbit?	septimus	12/17/99 11:39 a.m.
Re: ...But where would they orbit?	Grey	12/17/99 12:40 p.m.
I'm dissapointed in you guys...	Maxaminus	12/17/99 2:05 p.m.
Two possible definitions.	Dispatcher	12/17/99 9:33 p.m.
Re: I'm dissapointed in you guys...	SiliconDream =PN=	12/17/99 9:43 p.m.
Re: ...But where would they orbit?	Jägermeister	12/17/99 1:22 p.m.
Re: Internal orbits	Mark Levin	12/17/99 2:15 p.m.
Re: Internal orbits	Mage	12/17/99 2:32 p.m.
Re: Internal orbits	Mark Levin	12/17/99 2:38 p.m.
Re: Internal orbits	Mage	12/17/99 4:13 p.m.
Re: Internal orbits	Maxaminus	12/17/99 4:45 p.m.
Re: Internal orbits	Mage	12/17/99 11:06 p.m.
Re: Internal orbits	Mark Levin	12/18/99 12:42 a.m.
Re: Internal orbits	Mage	12/18/99 11:31 a.m.
Re: Internal orbits	Mr. Eez	12/17/99 4:27 p.m.
Re: Internal orbits	MacGuyver	12/17/99 4:49 p.m.
Re: Internal orbits	Mark Levin	12/17/99 5:02 p.m.
Re: Internal orbits	SiliconDream =PN=	12/17/99 9:42 p.m.
Uses for the Halo's axis...	Noctavis =PN=	12/20/99 3:31 p.m.
Stable Orbits (again)	Butcher	12/21/99 1:36 a.m.
Placing a satellite in the center of the Halo	Noctavis =PN=	12/21/99 10:35 a.m.
Re: Placing a satellite in the center of the Halo	Butcher	12/21/99 2:33 p.m.
Unstable orbits... Why use a halo orbit?	Noctavis =PN=	12/21/99 6:31 p.m.
Tides on the Halo	Butcher	12/21/99 7:03 p.m.
Re: Tides on the Halo	Someguy	12/21/99 8:00 p.m.
Re: Tides on the Halo	Butcher	12/21/99 9:35 p.m.
Re: soell	•Mimer	12/25/99 3:55 p.m.
Re: soell	Matt	12/27/99 11:53 a.m.
Re: soell	Daft Shadow =PN=	12/27/99 4:11 p.m.
Re: soell	Bachus	12/27/99 6:50 p.m.
Re: Unstable orbits... Why use a halo orbit?	SiliconDream =PN=	12/21/99 11:40 p.m.
Re: Internal orbits	Nathan	12/20/99 4:37 a.m.
Re: Rotations	Forensic	12/20/99 11:58 a.m.
Re: Rotations	SiliconDream =PN=	12/20/99 2:21 p.m.
Re: Rotations	btrinen	12/20/99 2:53 p.m.
Gravity	SyberSmoke	12/20/99 3:09 p.m.
Re: Gravity	SiliconDream =PN=	12/21/99 11:00 p.m.
Re: Rotations	Noctavis =PN=	12/20/99 3:11 p.m.
Re: Rotations	Aiden	12/20/99 8:08 p.m.
Spin that ring	L. Tankersley ("Cap'n Carnage")	12/20/99 5:12 p.m.
Re: Spin that ring	Dispatcher	12/20/99 9:43 p.m.
Re: Spin that ring	L. Tankersley ("Cap'n Carnage")	12/21/99 10:25 a.m.
Re: Spin that ring	Dispatcher	12/21/99 11:10 p.m.
L1? or L4-5?	Oddot	12/22/99 10:24 a.m.
Re: L1? or L4-5?	L. Tankersley ("Cap'n Carnage")	12/22/99 2:54 p.m.
Q: How do you spin the Halo?	Ironfist [CMG]	12/20/99 5:41 p.m.
Re: Internal orbits	Chris Huff	12/20/99 6:59 p.m.
Re: Internal orbits	Ringdude	12/20/99 7:18 p.m.
Re: Internal orbits	SiliconDream =PN=	12/21/99 11:06 p.m.
Re: Internal orbits	Someguy	12/21/99 11:11 p.m.
Re: Internal orbits	SiliconDream =PN=	12/22/99 4:06 a.m.
Re: Internal orbits	Thomas Magle Brodersen	12/21/99 3:06 a.m.