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> There is one ultimate sure-fire way to reduce space junk: launch stuff to very low orbits Really? If there's a collision in LEO, doesn't debris spray in all

> There is one ultimate sure-fire way to reduce space junk: launch stuff to very low orbits Really? If there's a collision in LEO, doesn't debris spray in all directions, including some in the direction of higher, more stable orbits?

enchiridion 6y ago
Not a physicist, but I doubt the debris would have the energy to reach geostationary orbits.
- SideburnsOfDoom 6y ago
  Not relevant? There are many orbits that are below geostationary and are also high enough to avoid atmospheric drag for a long time.
wizzwizz4 6y ago
In the direction, yes, but it would still cross the original orbit. You need a second collision to actually get stuff into higher orbits.
ravedave5 6y ago
With my limited knowledge of orbital mechanics I believe this wouldn't be a problem. It takes a lot of energy to move to a higher orbit. I would think the probability of enough energy to fling something to a higher orbit where it would be stable for a noticeably longer time would be very low. Think of exploding something 2 miles up the side of a mountain, what are the chances a piece goes another mile up the mountain. Like that but even harder.
mediaman 6y ago
This would just create an oblong orbit, which would still cause re-entry into thicker atmosphere for a portion of the orbit.
hinkley 6y ago
I thought the debris that gets lifted upward tends to go into elliptical orbits. Apogee would still create a significant amount of drag, wouldn't it?
- SideburnsOfDoom 6y ago
  Yes, I'm aware that orbital mechanics is not that simple, that's why I specifically didn't talk about "upward" as a higher orbit isn't necessarily caused by a push in that direction. Sibling comment ( https://news.ycombinator.com/item?id=26809297 https://news.ycombinator.com/item?id=26809297 ) is better at outlining that I was wrong: apparently a single impact cannot produce an entirely higher orbit, for debris sent in _any_ initial direction. At best, it produces elliptical orbits with a higher apogee, and the same drag at perigee.
xoa 6y ago
Just to add to sibling comments who already answered this, that isn't how orbital mechanics work (or else a lot of things would be much easier!). A good place to start reading is on Hohmann transfer orbits [1, 2]. They're commonly covered in the context of interplanetary travel, but the exact same principle applies to changing orbits around a single gravity well. The key take home as applied to here is that a single instantaneous addition of energy (delta-v) to an object in stable circular orbit just changes it to an elliptical orbit where the high point is determined by the added delta-v but the low point is the same as where it started. It takes a properly timed second instantaneous application of energy to stabilize at a different orbit. So any ejecta from a single collision will still orbit through whatever altitude they started at, and in turn will be affected by atmospheric drag at that point regardless of how much farther out they get at the high point. In principle it's of course not impossible that they could collide with something else already in a higher stable orbit, but the odds of that get very, very low particularly in the short time frame they have before decay assuming they're starting in VLEO. ---- 1: https://ocw.mit.edu/courses/aeronautics-and-astronautics/16-07-dynamics-fall-2009/lecture-notes/MIT16_07F09_Lec17.pdf https://ocw.mit.edu/courses/aeronautics-and-astronautics/16-... 2: https://solarsystem.nasa.gov/basics/chapter4-1/ https://solarsystem.nasa.gov/basics/chapter4-1/
- SideburnsOfDoom 6y ago
  That's a comprehensive answer, thank you. TIL.
- tgb 6y ago
  > high point is determined by the added delta-v but the low point is the same as where it started Is it the low point that is that same? I would have thought it was the current point (at time of delta-v addition), wherever that is, that must be part of the new orbit. Not that this is relevant for the topic at hand, just trying to check my understanding.
  - omegaham 6y ago
    This is correct. The simplification being made is that the original orbit was circular, so if you increase the debris' velocity, the current point is now the low point of the new orbit.

enchiridion 6y ago

Not a physicist, but I doubt the debris would have the energy to reach geostationary orbits.

SideburnsOfDoom 6y ago
Not relevant? There are many orbits that are below geostationary and are also high enough to avoid atmospheric drag for a long time.

wizzwizz4 6y ago

In the direction, yes, but it would still cross the original orbit. You need a second collision to actually get stuff into higher orbits.

ravedave5 6y ago

With my limited knowledge of orbital mechanics I believe this wouldn't be a problem. It takes a lot of energy to move to a higher orbit. I would think the probability of enough energy to fling something to a higher orbit where it would be stable for a noticeably longer time would be very low. Think of exploding something 2 miles up the side of a mountain, what are the chances a piece goes another mile up the mountain. Like that but even harder.

mediaman 6y ago

This would just create an oblong orbit, which would still cause re-entry into thicker atmosphere for a portion of the orbit.

hinkley 6y ago

I thought the debris that gets lifted upward tends to go into elliptical orbits. Apogee would still create a significant amount of drag, wouldn't it?

SideburnsOfDoom 6y ago
Yes, I'm aware that orbital mechanics is not that simple, that's why I specifically didn't talk about "upward" as a higher orbit isn't necessarily caused by a push in that direction. Sibling comment ( https://news.ycombinator.com/item?id=26809297 https://news.ycombinator.com/item?id=26809297 ) is better at outlining that I was wrong: apparently a single impact cannot produce an entirely higher orbit, for debris sent in _any_ initial direction. At best, it produces elliptical orbits with a higher apogee, and the same drag at perigee.

xoa 6y ago

Just to add to sibling comments who already answered this, that isn't how orbital mechanics work (or else a lot of things would be much easier!). A good place to start reading is on Hohmann transfer orbits [1, 2]. They're commonly covered in the context of interplanetary travel, but the exact same principle applies to changing orbits around a single gravity well. The key take home as applied to here is that a single instantaneous addition of energy (delta-v) to an object in stable circular orbit just changes it to an elliptical orbit where the high point is determined by the added delta-v but the low point is the same as where it started. It takes a properly timed second instantaneous application of energy to stabilize at a different orbit. So any ejecta from a single collision will still orbit through whatever altitude they started at, and in turn will be affected by atmospheric drag at that point regardless of how much farther out they get at the high point. In principle it's of course not impossible that they could collide with something else already in a higher stable orbit, but the odds of that get very, very low particularly in the short time frame they have before decay assuming they're starting in VLEO. ---- 1: https://ocw.mit.edu/courses/aeronautics-and-astronautics/16-07-dynamics-fall-2009/lecture-notes/MIT16_07F09_Lec17.pdf https://ocw.mit.edu/courses/aeronautics-and-astronautics/16-... 2: https://solarsystem.nasa.gov/basics/chapter4-1/ https://solarsystem.nasa.gov/basics/chapter4-1/

SideburnsOfDoom 6y ago
That's a comprehensive answer, thank you. TIL.
tgb 6y ago
> high point is determined by the added delta-v but the low point is the same as where it started Is it the low point that is that same? I would have thought it was the current point (at time of delta-v addition), wherever that is, that must be part of the new orbit. Not that this is relevant for the topic at hand, just trying to check my understanding.
- omegaham 6y ago
  This is correct. The simplification being made is that the original orbit was circular, so if you increase the debris' velocity, the current point is now the low point of the new orbit.