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All the low earth orbits decay due to low but meaningful resistance from the thin atmosphere; satellites like the SpaceX Starlink essentially are continuously "

All the low earth orbits decay due to low but meaningful resistance from the thin atmosphere; satellites like the SpaceX Starlink essentially are continuously "brough back to Earth" unless they periodically boost themselves up to maintain orbit height.

tgsovlerkhgsel 5y ago
How quickly though? Given the size of the constellations that are currently being launched, could all of LEO become an all-destroying debris cloud, forcing us out of LEO for a year or so until it has decayed? Possibly not a disaster now, but once people start relying on Starlink & co, it could be.
- lutorm 5y ago
  The orbital decay time depends on the ballistic coefficient of the body. This scales as mass/area, so is lower for small objects, meaning they decay faster. If the decay time for a Starlink satellite is a couple years, fragments from a collision will deorbit much faster.
  - dave333 5y ago
    Since all debris will return to near the collision point approximately every 90 minutes, there will be further collisions of bits of debris that will tend to reduce the size of the bits of debris and speed up the decay. This will be more pronounced if the original objects that collided have orbit planes that are nearer orthogonal.
renox 5y ago
Unfortunately that's too simple: imagine a collusion with a low orbit satellite which explodes, some part of the debris will be boosted to an higher height..
- PeterisP 5y ago
  No, that's not really how orbits work - after a collision or explosion, the orbit of every created shard will still pass through the point of collision, so if a satellite in circular LEO gets exploded, much of the debris will be boosted to a more elliptical orbit where the apogee may be higher, potentially much higher, but the perigee - where the majority of the drag happens, in a very nonlinear manner - will be lower than that LEO orbit or at the very worst case the same as it, having an elliptical orbit that comes down to the atmosphere, slowing down at every iteration. There's no physical way for a single event to bring something up from a low circular orbit to a higher orbit that's fully out of that low altitude zone, that requires circularization for which spaceships need to do another burn at the opposite (high) point of the orbit. If some circular orbit is in a LEO "gonna burn up soon" zone, then the debris from a crash there won't leave the zone because all the elliptical orbits that pass through points on that circle also have as much or more "gonna burn up soon" property.
  - renox 5y ago
    Nice explanation, thanks for correcting my mistake.

tgsovlerkhgsel 5y ago

How quickly though? Given the size of the constellations that are currently being launched, could all of LEO become an all-destroying debris cloud, forcing us out of LEO for a year or so until it has decayed? Possibly not a disaster now, but once people start relying on Starlink & co, it could be.

lutorm 5y ago
The orbital decay time depends on the ballistic coefficient of the body. This scales as mass/area, so is lower for small objects, meaning they decay faster. If the decay time for a Starlink satellite is a couple years, fragments from a collision will deorbit much faster.
- dave333 5y ago
  Since all debris will return to near the collision point approximately every 90 minutes, there will be further collisions of bits of debris that will tend to reduce the size of the bits of debris and speed up the decay. This will be more pronounced if the original objects that collided have orbit planes that are nearer orthogonal.

renox 5y ago

Unfortunately that's too simple: imagine a collusion with a low orbit satellite which explodes, some part of the debris will be boosted to an higher height..

PeterisP 5y ago
No, that's not really how orbits work - after a collision or explosion, the orbit of every created shard will still pass through the point of collision, so if a satellite in circular LEO gets exploded, much of the debris will be boosted to a more elliptical orbit where the apogee may be higher, potentially much higher, but the perigee - where the majority of the drag happens, in a very nonlinear manner - will be lower than that LEO orbit or at the very worst case the same as it, having an elliptical orbit that comes down to the atmosphere, slowing down at every iteration. There's no physical way for a single event to bring something up from a low circular orbit to a higher orbit that's fully out of that low altitude zone, that requires circularization for which spaceships need to do another burn at the opposite (high) point of the orbit. If some circular orbit is in a LEO "gonna burn up soon" zone, then the debris from a crash there won't leave the zone because all the elliptical orbits that pass through points on that circle also have as much or more "gonna burn up soon" property.
- renox 5y ago
  Nice explanation, thanks for correcting my mistake.