Ask HN: I need to plan and execute a highly coplex set of steps. Suggestions?

I need to plan out and execute a project with at least 200 discrete steps, many of the overlapped in time and interdependent, some of them cycles of action to repeat. An effort to put this into a Gantt chart only left me frustrated and overwhelmed. Suggestions for how to model such a project and make sure I am on track to complete it? The closest example would be someone doing a large scientific study with live subjects and multiple factors over time.