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0 pointssnaily8y ago0 comments

From first principles, I'm not seeing how a LEO collision pushes a significant amount of debris notably higher, but I'm certainly missing something:

Post collision, all debris orbits will still be passing through the point of collision. Any deflection with a vertical component (up or down towards the earth) will have a part of their orbit go through thicker atmosphere, which will make them deorbit faster. That leaves deflections which are in the plane spanned by the two orbits ("sideways" and "forwards/backwards"). If those deflections in any way slow down the piece of debris, that will also go through lower atmosphere and deorbit.

Disregarding debris under those effects, the remaining debris will have two more things going for it: They'll be out of the LEO orbit for a large part of their (now elliptic) orbits, and they'll be smaller so they'll slow down more from friction (due to the square-cube law).

Of course, cascading effects could still affect all satellites in LEO (and humanity's access to orbit for years), but it doesn't seem to me like it'd be a "permanent" issue in LEO? What am I not seeing?

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kobeya8y ago

When collisions are more frequent than once per orbit you get effects where more than one collision cause a bit of debris to have itself lifted. MOST debris is deorbited, but a small fraction is lifted into a higher orbit overall. As these collide with other objects the total mass of the system might go down (from reentry), but the number of objects and the frequency of collision goes up, continuing the process of some objects getting into higher energy orbits.

This is not too dissimilar to the process of evaporative cooling in a liquid, or gas escape from an atmosphere.

vanderZwan8y ago

> more frequent than once per orbit

My gut feeling says that statistically, even just going from one impact to two impacts being likely would require an immense density of satellites, let alone having more collisions than that.

Then there's also the fact that every impact would have a loss of kinetic energy (because it gets converted to heat as the objects deform), which would also make a reduction in orbit likely.

If the debris keeps fragmenting, which maybe could increase odds of impact, the remaining kinetic energy would be divided over each object. The smaller the debris gets, the more drag it should feel too, because of the square-cube law[0]. So that too would only make it more likely to deorbit.

[0] https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

kobeya8y ago

https://en.wikipedia.org/wiki/Kessler_syndrome

snrplfth8y ago

Not how orbits work. A collision can't cause, for example, an object with a circular orbit at 400km (passive reentry regime) to become fragments with a circular orbit at, say, 2000km (non-passive reentry regime.) Like snaily said, all fragments originating from a collision will still pass through the point of collision, which, if it is still in the upper atmosphere, will lead to reentry. Orbital debris is actually very dissimilar to gas escape.

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kobeya8y ago

This is not too dissimilar to the process of evaporative cooling in a liquid, or gas escape from an atmosphere.

vanderZwan8y ago

> more frequent than once per orbit

My gut feeling says that statistically, even just going from one impact to two impacts being likely would require an immense density of satellites, let alone having more collisions than that.

Then there's also the fact that every impact would have a loss of kinetic energy (because it gets converted to heat as the objects deform), which would also make a reduction in orbit likely.

[0] https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

kobeya8y ago

https://en.wikipedia.org/wiki/Kessler_syndrome

snrplfth8y ago

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