[danielvf]

That’s one of the key factors. It depends on the how high the orbit of the satellite is. For ones in LEO

- below 350 km, months

- 400km a year

- 500km five years

- 600km ten years

- 700km twenty five years

Etc.

However, when a satellite breaks up, the small pieces are much more affected by drag. Another is effect is that an explosion results in approximately 50% of the pieces having a lower orbit. So even though the Cosmos-Irdium collision happened at 700km, which would take about twenty five years to deorbit, in just five years, more than a quarter of the debris had deorbited.

[Cthulhu_]

When you put it like that, it doesn't sound as bad as, say, nuclear winter. 25-50 years of high debris, then slowly reducing remains. It's weird to imagine that if humanity would die out suddenly, our satellites and orbital space waste would only stay up there for what, 100 - 200 years more?

[danielvf]

You are right - it's not apocalyptic.

Particularly, since satellites in general are getting much lighter than they used to be (faster decay times, less mass in case of a collision, smaller target), as well as targeting lower orbits than we used to (most go to 400km-500km now).

Also, even in the event of everything in LEO blowing up, we can still launch to farther orbits / other planets.

[TeMPOraL]

> Also, even in the event of everything in LEO blowing up, we can still launch to farther orbits / other planets.

It'd be risky though, since you have to cross LEO to get there (unless you're willing to pay the extra cost of launching to absurd inclinations and correcting in space).

[jandrese]

It would take an unbelievably catastrophic Kessler syndrome to make it too dangerous to boost through LEO. It's not a game of Asteroids, we're talking about collisions on a yearly or possibly monthly timeframe. Bad enough to ruin LEO for satellites, but not so bad that it blocks you from space entirely.

[TeMPOraL]

I still think a believably catastrophic Kessler syndrome would be risky enough that NASA and others would refrain from sending manned missions through LEO at low inclinations.

It's not a game of Asteroids, but it's also not as thin as the asteroid belt.

[skykooler]

Only the stuff in low orbit. Communications satellites and the like in Molnya orbits or geosynchronous orbits will last millenia.

[TeMPOraL]

GEO stuff would stay for much longer, though; it's 36Mm up.

[jandrese]

Kessler Syndrome is very unlikely in GEO orbits. The reason is twofold: first the distances are enormous, but more importantly all of the satellites are traveling at the same speed in the same direction. Even a defunct satellite that didn't get put in a parking orbit and starts drifting will take years before it even has a chance of colliding with another satellite, and the odds of that collision are infinitesimal.

In LEO you have a completely different story. The distances are still large, but not as overwhelming as they are in GEO. Also, satellites are flying in every direction at very high relative velocities to one another. A piece of space trash could have thousands of potential collisions per day, so even if the odds of any one collision are small the cumulative odds start to add up over time.

Of course the other problem is that when we put people into space we put them in LEO. People have not ventured beyond LEO since the Apollo program. In the event of a full blown Kessler syndrome manned space flight would have to be put on hold for decades while we wait for the skies to clear up.