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SpaceX is planning to launch up to 42 000 satellites (there are about 3000 now). Cheaper $/kg leads to more space junk and higher risk of Kessler syndrome, that

by yread 6y ago

SpaceX is planning to launch up to 42 000 satellites (there are about 3000 now). Cheaper $/kg leads to more space junk and higher risk of Kessler syndrome, that doesn't need any qualifications, I think. If something goes wrong the fact that the cloud of debris will be there for 10 years and not 100 years is not a huge consolation

LeifCarrotson 6y ago
Timing is absolutely a huge qualification to Kessler syndrome. If the cloud of debris is gone in 5 years, that's a hurdle to some careers and a (hopefully) temporary shutdown for some businesses. Covid has taught us that the modern economy has traded a lot of robustness for profit and efficiency, and those would certainly be significant losses of billions or trillions of dollars, but it would be a small fraction of GDP, we would hopefully learn from the mistake, and we would still be a spacefaring species. If Kessler syndrome occurred among geostationary satellites, that could potentially be a problem for millions of years. That's six orders of magnitude different and definitely needs qualification.
- yread 6y ago
  But there is a lot more space in geostationary orbits and lot less stuff so the risk of chain of collisions is lower
  - duskwuff 6y ago
    There is far less space in geostationary orbit, because the locus of GEO is a one-dimensional ring above the equator.
    - fogof 6y ago
      It's true that there is less GEO real estate in this sense. But to kick off Kessler syndrome, you need two objects in different orbital planes so that they collide at very high speed. It wouldn't be possible for two defunct GEO satellites to collide, because two nearby GEO satellites are moving in the same direction at the same speed.
    - yread 6y ago
      but aren't the satellites in GEO stationary relative to one another? And if by chance they all get destroyed in collision the debris would mostly also stay in that ring so we could still launch rockets and have satellites in other orbits that don't cross it.
paulmd 6y ago
And this is exactly the sort of comment that grandparent addressed with their post. More stuff in orbit doesn't necessarily lead to higher risk of a catastrophic kessler syndrome event, if it's low-earth orbit. The risk is not the same as geosynchronous where it can stay there forever. The satellites themselves (and even the debris if there is a collision) will decay on a very short-term basis (single-digit number of years). By making launch cost-per-kg cheaper, it is now plausible to put things in LEO instead of geo or other orbits. And doing that probably actually reduces the risk of a catastrophic event, even if there is more stuff. Possibly higher risk of a smaller event, sure, but that is true of anything that puts more stuff in space. That's a generic argument that we shouldn't be doing anything in space at all, which I think is not compelling.
whimsicalism 6y ago
> If something goes wrong the fact that the cloud of debris will be there for 10 years and not 100 years is not a huge consolation Seems like a pretty big consolation to me, no?
- aardvarkr 6y ago
  No kidding. Order of magnitude
Strilanc 6y ago
How does the cloud of debris stick around? For context, I've played Kerbal so I know a bit about orbits but not much. My intuition is that the velocities involved in being in orbit in the first place are so big (7 kilometers per second according to a quick search) that the orbit of the debris won't be substantially different, so it will still decay. Even if you give enormous kicks to the debris, most of it will end up with orbits intersecting the earth. The ones that don't will still intersect the original collision location, and so still experience decay during that part of their orbit. Basically, to change your orbit you need to boost once to push the other side of the orbit out and then again at the other side to push the original side out. A collision can only give one of the boosts, and so is sort of inherently bad at moving the orbit.
- KiwiJohnno 6y ago
  You are totally correct (and yay KSP!) But the danger is the debris that is ejected from a collision at a lower orbit would then collide with debris that is at a higher orbit. The debris from the 2nd collision would have its original periapsis, which may be high enough to stick around for decades.

by yread 6y ago

LeifCarrotson 6y ago

Timing is absolutely a huge qualification to Kessler syndrome. If the cloud of debris is gone in 5 years, that's a hurdle to some careers and a (hopefully) temporary shutdown for some businesses. Covid has taught us that the modern economy has traded a lot of robustness for profit and efficiency, and those would certainly be significant losses of billions or trillions of dollars, but it would be a small fraction of GDP, we would hopefully learn from the mistake, and we would still be a spacefaring species. If Kessler syndrome occurred among geostationary satellites, that could potentially be a problem for millions of years. That's six orders of magnitude different and definitely needs qualification.

yread 6y ago
But there is a lot more space in geostationary orbits and lot less stuff so the risk of chain of collisions is lower
- duskwuff 6y ago
  There is far less space in geostationary orbit, because the locus of GEO is a one-dimensional ring above the equator.
  - fogof 6y ago
    It's true that there is less GEO real estate in this sense. But to kick off Kessler syndrome, you need two objects in different orbital planes so that they collide at very high speed. It wouldn't be possible for two defunct GEO satellites to collide, because two nearby GEO satellites are moving in the same direction at the same speed.
  - yread 6y ago
    but aren't the satellites in GEO stationary relative to one another? And if by chance they all get destroyed in collision the debris would mostly also stay in that ring so we could still launch rockets and have satellites in other orbits that don't cross it.

paulmd 6y ago

And this is exactly the sort of comment that grandparent addressed with their post. More stuff in orbit doesn't necessarily lead to higher risk of a catastrophic kessler syndrome event, if it's low-earth orbit. The risk is not the same as geosynchronous where it can stay there forever. The satellites themselves (and even the debris if there is a collision) will decay on a very short-term basis (single-digit number of years). By making launch cost-per-kg cheaper, it is now plausible to put things in LEO instead of geo or other orbits. And doing that probably actually reduces the risk of a catastrophic event, even if there is more stuff. Possibly higher risk of a smaller event, sure, but that is true of anything that puts more stuff in space. That's a generic argument that we shouldn't be doing anything in space at all, which I think is not compelling.

whimsicalism 6y ago

> If something goes wrong the fact that the cloud of debris will be there for 10 years and not 100 years is not a huge consolation Seems like a pretty big consolation to me, no?

aardvarkr 6y ago
No kidding. Order of magnitude

Strilanc 6y ago

How does the cloud of debris stick around? For context, I've played Kerbal so I know a bit about orbits but not much. My intuition is that the velocities involved in being in orbit in the first place are so big (7 kilometers per second according to a quick search) that the orbit of the debris won't be substantially different, so it will still decay. Even if you give enormous kicks to the debris, most of it will end up with orbits intersecting the earth. The ones that don't will still intersect the original collision location, and so still experience decay during that part of their orbit. Basically, to change your orbit you need to boost once to push the other side of the orbit out and then again at the other side to push the original side out. A collision can only give one of the boosts, and so is sort of inherently bad at moving the orbit.

KiwiJohnno 6y ago
You are totally correct (and yay KSP!) But the danger is the debris that is ejected from a collision at a lower orbit would then collide with debris that is at a higher orbit. The debris from the 2nd collision would have its original periapsis, which may be high enough to stick around for decades.