I don't know that the debrise field is all that thick. You've had 10 years for random orbits to decay, and for the objects in stable orbits to collect each other, and scrappers have been conducting salave ops for that long too. There's still allot of working stations in the various orbits inhabited by hundreds of thousands of people. The five listed sofar are; Elegua, (HEO), 120,000 people, VoNguyn (Geo), 100,000+ people, Vishnukam (?), 10,000 + people Shenlong, (MEO), ? people In addition there are multiple Tincan stations and smaller torus. You can assume that by now they've managed to at least clear their own orbital paths and provide enough clear space that they can be easily serviced by shuttles from the moon and lagrange stations. I think it's likely that LEO is still a mess but the killsats have probably been gradually clearing that space.

The Kessler syndrome is a cool phenomenon. I actually had my players accidentally trigger it in a past campaign when they didn't check the cargo of their Orion rocket carefully enough. However, it is not able to prevent space access. When things collide and break up they tend to remain in their original orbits, with a bit of extra spread. In the aforementioned Orion case, we got a nasty debris ring (or rather, torus) along the orbit of the rocket and everything it hit. Junk in very eccentric orbits tend to fall into the atmosphere. Also, the density of junk is very low. If you spread out a big object like the ISS along its orbit in gram-sized pieces there would be one every eight meter. Assume the width of the debris torus was 10 kilometres and you would get one piece per 12 million cubic kilometres! Even taking into account that they sweep by fast, just going through this volume once will not have a high risk. The problem is that anything *staying* in the volume is going to get hit sooner or later and suffer a cascade. But it takes a while. Also, the higher you go, the more space there is and the less effective the cascade becomes: above a few thousand kilometres I think it does not happen over realistic timescales at all, if I remember Kessler's papers right. The killsats are needed because it is relatively easy to make something that is lucky enough, armoured enough or has lidar/point defences enough to get through the field. That said, Kessler cascades are no laughing matter in EP. Consider what would happen if a O'Neill colony broke up over Mars. There is so much expensive and vital infrastructure there that it would be a major all-hands-on-deck situation. Shooting down debris is hard.

Or you could do like in the anime Planetes and actually have spacefaring garbage collectors who's sole job it is to pick up and process debris that could be a hazard to orbital installations before it makes it to the atmosphere or anywhere else dangerous.

Just noticed this video advertising Lockheed Martin's Space Fence concept: http://www.youtube.com/watch?v=7SJdN90vT04&feature=player_embedded Some nice graphics there that might inspire gaming. Of course, these displays show the good old days when there were just hundreds of thousands of objects to track... The Martian counterpart of that imagined control room would be a vast simspace run by a team of very competent AGIs and transhumans, running hundreds of infomorphs and AIs on the task of keeping track of anything anywhere close to Mars. Imagine the complexity when a comet fragment sweeps through their space. Adventure idea: the villains (or PCs!) set up an attack somewhere months ahead by launching various pieces of debris on trajectories carefully designed to overload the defenses - you can hit 90% of them, but there will always be a set that hits the sensitive installations. Or they blind the fence sensors at a strategic moment so something can slip through.