A single impact can't put something into a higher circular orbit-- it can create an elliptical orbit with a higher apogee (max distance), but the correspondingly nearer perigee (closest approach) means that it experiences more atmospheric drag and falls out of orbit faster.

I thought so too, but apparently this is not universally true. Some of the debris can be put in an orbit with a longer lifetime than the original satellite. I got into a long twitter argument with experts in this field, and I was proven false: some of the debris can have longer orbital lifetime and go to higher orbit.

EDIT: Here: https://twitter.com/SpaceJosh/status/1119721780254371840

Always embarrassing to make a fool of myself on the Internet, but losing an argument IS a very effective way of learning.

You said:

> That seems unlikely, as that requires like 11km/s which is more than the sum of the two velocities[...]

Isn't the first problem here that you're assuming a spherical cow in a vacuum physics problem? Two satellites colliding aren't two indivisible pebbles colliding.

They're going to pulverize on impact, and some of the now-expanding debris cloud might even contain combustibles the satellites were carrying.

The debris also won't only collide once, there'll be a series of rapidly occurring re-collisions. Some of those might impart extra velocity on some of the expanding debris.

Galilean cannon?

Granted, I don't know the math and this is intuition from Kerbal Space Program, but I'm not sure that's right. Wouldn't two objects colliding at 0° and 90° orbits result in a higher apoapsis and the same periapsis? Wouldn't it be equivalent to a normal impulse? Some pieces of one of the satellites would have more energy than they did before the impact.

You are correct. The result would be an elliptical orbit, though, not the circular orbit that the post you replied to mentioned.

I don't know if the person edited it after you replied, though.

Kerbal Space Program taught me so much, I now realize. I was able to follow and visualize everything in this thread due to that videogame. Neat.

I don't think the perigee needs to be lower? Consider a collision fragment that breaks off tangentially to the orbital path and moves faster than the speed needed to maintain a circular orbit: its new perigee should be the radius of the circular orbit, but the apogee will be higher.

Higher orbits require higher velocities, which aren't going to be reached by collision debris.

It’s not likely but definitely not impossible.

https://youtu.be/2UHS883_P60

For the sake of completeness, did a little digging, looks like it did happen in fact - https://celestrak.com/events/collision/

Collisions can absolutely eject debris at a higher velocity than either of the initial impactors.

Gravity is directional.