VECTOR: Asteroids vector ROM contents

Some time ago I could swear that someone created a program to view and 
generally make sense of the contents of the Asteroids Vector ROM, ie it was 
possible to look at how the saucers, asteroids, character set, etc were 
defined for use by the main program code.

Despite a good look around though I can't see any signs of such a program 
(maybe I'm using the wrong search string).

Anyhow, does this ring any bells with anyone?

Failing that, does anyone know how to make sense of the vector ROM? I ask 
because I'm currently messing around with writing an Asteroids program 
(purely for fun and as a programming learning exercise) and would like to 
get the thing to look as accurate as possible.


Thanks,
Phil