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Lakeshore
An author of no particular popularity

Jay Lake
Date: 2010-12-11 16:33
Subject: [help] Satellite orbit question
Security: Public
Tags:help, science
I swear this went through Link Salad in the last year or two, but I cannot run it down.

Is there a stable configuration for extremely long-term orbits (millennia or more) for artificial satellites? I recall reading that at least one satellite has been placed in such an orbit. I'm trying to sort out if that's true, and if so, is there a name for such an orbit?

Why, yes, this is rocket science.

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Elizabeth Coleman
User: criada
Date: 2010-12-12 00:36 (UTC)
Subject: (no subject)
Put it in one of the LaGrange points?
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jackwilliambell
User: jackwilliambell
Date: 2010-12-12 00:44 (UTC)
Subject: (no subject)
I assume you mean 'Earth orbit'.

In any case, Lagrange orbits are very stable.http://en.wikipedia.org/wiki/Lagrange_orbit

L4 and L5 are the most stable and L1 the least (as best I remember).

Some things to point out: (1) Close passing asteroids can mess with even stable orbits (if close enough) (2) Within a Lagrange point there might be multiple masses, each of which is doing a complicated little circular dance; so if you have more than one satellite you might have collisions over that long a period (3) Over a millennia dust abrasion and micrometeors are going to be major issues (4) All Lagrange points are outside the Earth's magnetosphere (aka, the 'Van Allen Belt'), meaning they get the full brunt of solar storms and other extant radiation.
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Kelly Green
User: saycestsay
Date: 2010-12-12 00:54 (UTC)
Subject: (no subject)
You mentioned it during FOOTPRINTS slushing :)
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Jay Lake
User: jaylake
Date: 2010-12-12 01:02 (UTC)
Subject: (no subject)
Brain, brain, what is brain...
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Kelly Green
User: saycestsay
Date: 2010-12-12 01:40 (UTC)
Subject: (no subject)
zombie food?
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jtdiii
User: jtdiii
Date: 2010-12-12 01:48 (UTC)
Subject: (no subject)
I was beaten to the Lagrange points.

But there is another very stable orbital position... Sitting on the Moon's surface.
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(no subject) - (Anonymous)
Jay Lake
User: jaylake
Date: 2010-12-12 15:53 (UTC)
Subject: Re: I thought I heard someone say "rocket science."
Sorry, I was unclear. I am thinking of a fictional planet with no major moons, otherwise Earthlike in mass, orbit, etc.

(And I swear I saw an article about an artificial satellite in a million-year+ orbit...)
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(no subject) - (Anonymous)
Jay Lake
User: jaylake
Date: 2010-12-12 17:34 (UTC)
Subject: Re: I thought I heard someone say "rocket science."
Thanks! And yes, this can be a dysfunctional orbit -- the artefact is abandoned, but still orbiting. So I'll just leave it as "high orbit".
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(no subject) - (Anonymous)
Jay Lake
User: jaylake
Date: 2010-12-12 17:51 (UTC)
Subject: Re: I thought I heard someone say "rocket science."
And I give you...

The checkered panels showed plentiful signs of both the original damage that had slain all occupants, and the millennium of micrometeroids that had since peppered the station. Still, it was in rather good shape.

As the very, very old joke went, it was not remarkable that the dog spoke well, it was remarkable that the dog spoke at all.

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(no subject) - (Anonymous)
Jay Lake
User: jaylake
Date: 2010-12-12 18:07 (UTC)
Subject: Re: I thought I heard someone say "rocket science."
Well-done on the -ite/-oid call, too. ;)

I actually had to look that up to make sure I got it right...
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(no subject) - (Anonymous)
Jay Lake: signs-dont_jay_walk
User: jaylake
Date: 2010-12-12 18:22 (UTC)
Subject: Re: I thought I heard someone say "rocket science."
Keyword:signs-dont_jay_walk
I take the credit for being smart enough to know I needed to look it up, and knowing what to look *for*... :D
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mikandra
User: mikandra
Date: 2010-12-12 03:24 (UTC)
Subject: (no subject)
wot he said.

Also, I don't think it's sufficiently clear from the above that Earth's LaGrange points are not orbits around Earth; they are points relating to Earth's orbit around the sun.

You want to make sure a device stays where you put it for milennia, orbiting Earth? I second jtdiii's suggestion: stick it on the surface of the Moon.

Otherwise, I'd go for something like geostationary orbit. It depends what your aim is.
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(no subject) - (Anonymous)
mikandra
User: mikandra
Date: 2010-12-12 03:51 (UTC)
Subject: (no subject)
agree, but I'm not sure if any of the other commenters were. LaGrange points refer to the relationship of two bodies, not one. So it depends on what orbit we're talking about. I haven't gone into it in this much detail, but I imagine the Earth-Moon LaGrange points would be less stable than the Earth-Sun ones.
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(no subject) - (Anonymous)
mikandra
User: mikandra
Date: 2010-12-12 04:04 (UTC)
Subject: (no subject)
The question remains if in the long term E-L L4 or L5 would be more stable than geostationary orbit.

I think it also depends on how tightly you define 'stable' for the sake of writing fiction. It could mean something very different if all you want is for the device not to crash back to Earth or wander off somewhere else, or if you want to be able to pinpoint it milennia later.
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