Crash clock says satellites in orbit are three days from disaster | Hacker News Reader

Crash clock says satellites in orbit are three days from disaster

newscientist.com

10 pointsBreadmaker7 comments

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.

Wait, are you saying each Starlink sateline is 16 thousand square miles large?

The surface area of the sphere at their altitude divided by 14k satellites gives each 16k square miles of surface area.

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.

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.

https://en.wikipedia.org/wiki/Cross_section_(physics)

It would be ironic if Starlink made Musk's goals of getting to Mars impossible because of an inescapable debris field.

At this point I think it's entirely expected that a capitalist corporation will gleefully ignore any and all external consequences

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