Suppose I wanted to answer the question Will Starman/Roadster pass particularly close to any asteroids in the next few years? or try to predict satellite conjunctions around Earth (e.g. Celestrak's SOCRATES), and I had ephemerides, TLEs, or interpolatable tables of state vectors.
I could propagate those in small time steps, calculate all $N$ positions and all $N(N-1)/2$ distances and search for any below a distance $d_{conj}$, but that might not be the most efficient way to do this.
Question: What are the algorithmic methods or techniques to do this kind of search more efficiently? Assume the propagators return a six-vector (position and velocity). I need an explanation or authoritative reference, not just a name-drop.
This question is distinct from Algorithmic methods or techniques to find conjunctions in high N Keplerian element ensembles? because it specifically asks about methods that operate on State vectors (either tabulated or propagated on demand) which may include n-body effects (e.g. the Sun moves, Jupiter does its thing, etc.)