Talk:Orbital decay

Decay resulting from third-body interactions

For many orbits, e.g. selenocentric orbits, atmospheric interaction cannot be the primary cause of orbital decay. Instead, isn't it brought about by the gravitational attraction of other nearby masses -- primarily the Earth in the case of selenocentric orbits? (sdsds - talk) 08:09, 3 February 2008 (UTC)

Why do you think so? The Moon has a much thinner atmosphere, but some atmospheric drag still exists, and I'd expect it to dominate gravitational interaction from the Earth on selenocentric orbits close enough to the Moon. So these should be either stable on human timescales (no orbital decay at all) or decay slowly due to the weak atmospheric drag. --Roentgenium111 (talk) 19:08, 4 April 2012 (UTC)

No, you're quite mistaken; the drag from Earth's (and Moon's) atmosphere is negligible near the Moon, yet most orbits aren't stable at all; see Lunar orbit. The cause is mass concentration (astronomy); see below. JustinTime55 (talk) 19:54, 19 February 2014 (UTC)

Gravitational radiation

While orbital decay from gravitational radiation is in theory possible, I know of no data to suggest it happens with man made satellites. Probably because for things the size of satellites (say, the ISS) gravitational radiation would work on the scale of billions of years. Can we please remove this section. — Preceding unsigned comment added by 216.165.95.66 (talk) 03:06, 12 September 2013 (UTC)

I quite agree; it doesn't really have anything to do with real-world orbital decay. Also, it is uncited, so I am moving it here:

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Main article: Gravitational wave

Whenever two masses orbit each other, the combined effect of the spacetime curvature of the moving objects produces gravitational waves which carry away orbital energy. For small masses this effect is negligible, but for very massive objects like black holes and neutron stars the energy carried away can be rapid enough to cause their orbits to spiral in on each other, eventually merging the two masses.

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I think this is what comes of a little too much physics, and not enough engineering. JustinTime55 (talk) 21:36, 19 February 2014 (UTC)

Mascons: another cause of orbital decay

This article seems to neglect the effects of mass concentration (astronomy), which is a well-known cause of decaying lunar orbits. This is not a tidal effect, which implies significant fluidity of the body. Mascons are essentially rigid, uneven distributions of matter. JustinTime55 (talk) 19:13, 19 February 2014 (UTC)

I don't think mascons cause orbital decay. Orbital decay is really a reduction in potential energy of the orbiter. Mascons, on the other hand, don't cause a reduction in potential energy and thus cause the orbit to become unstable but not decayed. This instability can lead to erratic orbits where the orbit becomes more and more eliptical, it can lead to the orbiter crashing into the body its bound to, or it can fly off into space. None of these are decay.

That said, mascons can definitely pull an object into an orbit where one of the effects of orbital decay can take place. But calling mascons a tyep of orbital decay isn't correct. Fresheneesz (talk) 23:08, 11 December 2015 (UTC)

Oxygen-bearing ... or not

Why does the atmosphere have to be oxygen-bearing? Well, because it says "burns up", and technically, burning cannot occur without oxygen. Of course, if the atmosphere is sufficiently dense (like Earth's), a great deal of heat is generated, and the object could melt and break up (pseudo-"burning") even without oxygen. We need to give this some thought to word it clearly and accurately, so it's general enough for any situation. (Or does it really need to be? In the real world, we're mostly concerned with Earth satellites; maybe Mars or Venus orbiters.) JustinTime55 (talk) 16:00, 20 February 2014 (UTC)

I agree that burning is combustion, but the oxidant doesn't have to be oxygen (though it usually is). I don't know offhand whether any planetary atmospheres contain any oxidizers other than oxygen. But I'm not clear about your comment - I don't see any reference to oxygen in the article. Are you referring to "...where the primary has an atmosphere, it burns, explodes, or otherwise breaks up in [the primary's] atmosphere..."?

If so I agree with your sentiment that burning isn't an appropriate word to use. And the object doesn't necessarily fully vaporize or otherwise transform - occasionally portions or most of the object survive to impact. So my sense is that the sentence needs to be restructured. How about '...where the primary has an atmosphere, portions or the entire object might melt, vaporize, explode, or otherwise break up in its atmosphere...'? (I assume explosions are usually caused by high thermal gradient stress, especially for natural objects, but could involve chemical reactions as well, perhaps especially for artificial objects.) But I've made no change yet. Opinions appreciated.--H Bruce Campbell (talk) 11:11, 28 October 2016 (UTC)