I have trouble comprehending how a collision would happen, in 3d space, even with a "14000 starlink satellites" (16k square miles each, on average), with something like 100ft being enough for them to pass over each other.
I thought most of the maneuvers were to maintain large margins of safety, not prevent definite collisions.
estimator7292 1 days ago [-]
Because the orbits largely aren't 3D. These constellations orbit at the same altitude. Altitude changes are very expensive because you can't just go "up", you have to go "forward" faster. "Down" means slowing your orbit.
Two objects at different altitudes cannot maintain the same speed and relative positions. A higher orbit necessarily must have a higher velocity than a lower orbit. If you try to distribute your constellation across multiple orbital altitudes they'll slowly drift out of sync without constant thrust.
So these constellations trace out different and intersecting paths across the surface of the same sphere, not a 3D shell around that sphere.
foxyv 1 days ago [-]
The problem is that the satellites are moving very fast and there are a lot of them. The mean free path may be very long, but if the satellite is moving very quickly it will cover that distance fairly often. This means that they will have to actively avoid collisions fairly often.
I thought most of the maneuvers were to maintain large margins of safety, not prevent definite collisions.
Two objects at different altitudes cannot maintain the same speed and relative positions. A higher orbit necessarily must have a higher velocity than a lower orbit. If you try to distribute your constellation across multiple orbital altitudes they'll slowly drift out of sync without constant thrust.
So these constellations trace out different and intersecting paths across the surface of the same sphere, not a 3D shell around that sphere.
https://en.wikipedia.org/wiki/Cross_section_(physics)