How do satellites not crash into each other?

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screen317
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Re: How do satellites not crash into each other?

Postby screen317 » Mon Aug 22, 2016 5:07 pm UTC

Pardon the ignorant question, but for all of the debris in or near LEO, why does it not all eventually fall out of orbit since it has no thrust capabilities? Or is it just a slower process than I'm imagining?

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Re: How do satellites not crash into each other?

Postby gmalivuk » Mon Aug 22, 2016 7:30 pm UTC

It's a very slow process on human scales.
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Re: How do satellites not crash into each other?

Postby Eebster the Great » Mon Aug 22, 2016 11:15 pm UTC

It depends on how low the orbit is. Skylab burned up just over six years after launch. It had an altitude of 434-442 km, which is actually higher than the ISS and thus higher than cubesats. I think most LEO satellites have an orbital lifetime of less than a decade. In particular, during solar maxima every 11 years the atmosphere expands, and drag greatly increases.

Also, it's not true that satellites have no rockets. Some don't, but most satellites with a significant pricetag (including all in GEO) do have small thrusters which are required to maintain a constant orbit and (in the case of GEO) move to a higher "graveyard" orbit at the end of their life.

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Re: How do satellites not crash into each other?

Postby Neil_Boekend » Tue Aug 23, 2016 6:59 am UTC

Also there is some limited research in electrodynamic tethers, which use the Earth as a reaction mass instead. But for now it seems it's cheaper to stick some rocket motors on it, like the very reliable and popular hydrazine rocket. Hydrazine is a hypergolic monopropellant: it explodes without an ignition source AND without a separate oxidizer. It just needs a metal katalyzer on which you kinda spay the stuff. AFAIK that means only 1 valve required which makes it light and very reliable, but I'm no rocket engineer (just a curious engineer, who has read most of Ignition! (PDF)).

Edit: fixed malformed BB tags and mismatched parentheses
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Re: How do satellites not crash into each other?

Postby gmalivuk » Tue Aug 23, 2016 11:48 am UTC

Eebster the Great wrote:Also, it's not true that satellites have no rockets.
Sure, but it is true that all LEO debris has no rockets.
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Re: How do satellites not crash into each other?

Postby Eebster the Great » Tue Aug 23, 2016 9:47 pm UTC

gmalivuk wrote:
Eebster the Great wrote:Also, it's not true that satellites have no rockets.
Sure, but it is true that all LEO debris has no rockets.

Well probably no functioning rockets . . .

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Re: How do satellites not crash into each other?

Postby Sableagle » Thu Aug 25, 2016 8:03 pm UTC

Eebster the Great wrote:But all those orbits will pass through the same (comparatively small) volume occupied by geostationary satellites every day, right?


Isn't a geosynchronous orbit below the geostationaries around the equator and north or south of them at apogee?

The truly geostationary must be a circle, never mind a torus, but the geosynchronous are a rather more complicated shape with a groove around it.

LEOs are all over the damn show, with many going not-quite-polar so they get to sweep the Earth's surface north-to-south and south-to-north on a track that slowly shifts around the Earth to cover the whole surface with some number of orbits. It's handy for taking pictures of all sorts of stuff.

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Re: How do satellites not crash into each other?

Postby Eebster the Great » Thu Aug 25, 2016 11:46 pm UTC

What the hell happened to your post?

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Last edited by Eebster the Great on Sat Aug 27, 2016 9:26 pm UTC, edited 2 times in total.

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Re: How do satellites not crash into each other?

Postby Sableagle » Sat Aug 27, 2016 6:28 pm UTC

Those were kind of off-topic, so I used a footnote-sized font. Someone apparently dislikes that font size and, rather than returning the off-topic to normal size and making the on-topic large ...

... did his or her thing.


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Re: How do satellites not crash into each other?

Postby Copper Bezel » Sat Aug 27, 2016 9:08 pm UTC

It's not March though?
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Re: How do satellites not crash into each other?

Postby Sableagle » Sat Aug 27, 2016 9:27 pm UTC

So, anyway, yeah, they have those repulsion fields from Dune that bounce anything coming at them too fast but let the shuttle dock with them to refuel them or recalibrate their instruments or whatever as long as (1) we still operate shuttles and (2) it approaches at quite low relative velocity.
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Re: How do satellites not crash into each other?

Postby Zohar » Sun Aug 28, 2016 12:05 am UTC

Copper Bezel wrote:It's not March though?

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Re: How do satellites not crash into each other?

Postby gmalivuk » Sun Aug 28, 2016 2:21 pm UTC

There does seem to have been a bit of a hiatus, though, so it's understandable that the youth of today would be unaware that the Baron predates the Madness by nearly two years.
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screen317
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Re: How do satellites not crash into each other?

Postby screen317 » Fri Sep 02, 2016 5:09 pm UTC

gmalivuk wrote:It's a very slow process on human scales.


Thank you. So to clarify, mankind is currently generating LEO debris faster than it is currently disintegrating?

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Re: How do satellites not crash into each other?

Postby Tyndmyr » Fri Sep 02, 2016 5:18 pm UTC

Oh, definitely.


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