> If there is no collision, yes you're right, but if there is one.... Stuff gets thrown into various orbits. Most of the debris will deorbit quickly, but a small percentage can get a substantial kick and go higher.

That's a misleading description.

While a collision may increase an object's apogee, it will be in an elliptical orbit: it will always intersect the orbit where the collision happened.

This isn't just a collision thing either: all spacecraft do this[1] as a first step (move to an elliptical orbit), and then typically relight their engines at the apogee in order to circularize their orbit.

---

1. https://en.wikipedia.org/wiki/Hohmann_transfer_orbit

Are you sure? My KSP intuition tells me this is wrong.

Orbits are circular and constant (accurate enough for my argument). An impact might cause some debris to go up, but when the debris that went up comes back around to the same spot in its orbit, it will again be going up. Well, extrapolate that backward a bit and you realize the debris that is going up was inside the atmosphere moments before.

In other words, if an instant impulse causes an orbit to have a higher apoapsis, it must also lower its periapsis. Which means the piece will go deeper into the atmosphere, and you don't come back from deep in the atmosphere.

> Stuff gets thrown into various orbits. Most of the debris will deorbit quickly, but a small percentage can get a substantial kick and go higher.

Only at apoapsis. But, any item thrown into an orbit with a significantly higher apoapsis will very likely have a significantly lower periapsis. So even for high-energy fragments, each orbit should have a period of passing through a higher-drag part of its orbit, and lose energy relatively quickly.

Significantly, the periapsis can never be lower than the altitude that the collision occurred. The worst case, IIRC, is for fragments ejected in the direction of orbital travel at the time of collision. But even then, they'll still spend some time in whatever drag environment they were in beforehand.

That's not to say collisions are fine, but nothing is going to get thrown into random high low-eccentricity orbits where they hang around and pose a threat for decades or more.