> generally when two satellites collide some debris can be shot at a higher orbit which will take forever (or will not) reenter atmosphere.
The lowest point of the new orbit (perigee) is guaranteed to be no higher than the point of collision. Fragments after the collision have no further propulsion, so their new orbit must initially include the point of collision, and can only decay from there. This can also be seen on your scatterplot.
Moreover, the time to decay is most strongly influenced by the perigee, as the atmosphere is the strongest there. If a satellite on an low orbit (decay in decades) explodes, those fragments that "reach a higher orbit" will still (due to the low perigee) decay back to a near-circular orbit in decades.
A collision can increase the lifetime for some of its fragments, but not by multiple orders of magnitude (unlike a circular higher orbit).
Your video link also nicely shows that fragments with a low perigee will decay quickly, no matter how high their apogee is.
Yes, this is true, but for this to not be a problem, it also has to suppose that those higher-flying bits of debris don't subsequently collide with other higher-flying satellites.
The Chinese test also happened around 350km higher then Starlink satellites (850km). The natural deorbit time at that altitude is already over 100 years vs under 5 years at 500km.
Also it was literally the worst possible collision being an intentional head on collision. Satellites accidentally hitting each other on orbit are very unlikely to hit each other head on as it is very uneconomical to put satellites in a reverse orbit that low (there is a reason why we do rocket launches towards east if possible)
The lowest point of the new orbit (perigee) is guaranteed to be no higher than the point of collision. Fragments after the collision have no further propulsion, so their new orbit must initially include the point of collision, and can only decay from there. This can also be seen on your scatterplot.
Moreover, the time to decay is most strongly influenced by the perigee, as the atmosphere is the strongest there. If a satellite on an low orbit (decay in decades) explodes, those fragments that "reach a higher orbit" will still (due to the low perigee) decay back to a near-circular orbit in decades. A collision can increase the lifetime for some of its fragments, but not by multiple orders of magnitude (unlike a circular higher orbit).
Your video link also nicely shows that fragments with a low perigee will decay quickly, no matter how high their apogee is.