When I read the eponymous book I always wondered why would a civilisation that could employ vast amounts of compute power lack long-term predictions on orbit trajectories - I would imagine they had that exquisitely refined to levels we would never bother to reach. Also, they are uniquely well suited for deep space travel by the very nature of their easily paused metabolism, so I assume they would have expanded to each and every suitable planet and built extraplanetary habitats.

BTW, this is a lovely solution. Step by step simulation is always the last resort, useful to gain a better understanding of how a system behaves, but not a great long term thing if you actually understand the system.