The third version of the Cambridge Rocketry Simulator consists of three parts to simulating a high power rocket flight. First the user is able to build a rocket from basic components using a GUI. Second, a verified and reviewed physics model simulates the rocket flight, this includes a Monte Carlo wrapper to quantify the uncertainty in dynamics and atmosphere. Finally, the visualization of the resulting trajectories includes nominal performance and uncertainty analysis, e.g. a splash-down region with confidence bounds. The project is available on SourceForge, and is written in Java (GUI), \CC (simulation core) and Python (visualization). While all parts can be executed from the GUI, the three components share information via XML, accommodating modifications, and re-use of individual components. The software can used to simulate the flight of unguided rockets, with both design and operational applications.