A Boltzmann equation for debris criticality studies ?

In a previous entry on prompt critical space debris, I was really mentionning the possibility of igniting a chain reaction in low earth orbit by the continuing add-on of space debris in LEO.

At some point, a colleague of mine and I looked into devising a transport equation similar to the one we use in neutron transport theory in order to evaluate what, we in the nuclear engineering world call criticality studies. Being critical is one thing, but when a system is "prompt critical", delayed neutrons cannot slow down a chain reaction yielding a very hazardous situation.

It would be worth looking into in light of the recent chinese test. Sure

"it does not pose a threat to any country"

for the moment, except that we are talking about a potential substantial increase of particles in orbit beyond the sum of all the debris from just the target of that test. What is really interesting is that there is a loss factor: drag from earth atmosphere has the ability to remove some of these debris over time. Yet, we don't really know how to fit experiments with observations. Some are attempting to do just that within the Robust Mathematical Modeling framework.

This is timely, especially four years after what happened in orbit.