  This paper introduces a novel Monte Carlo (MC) method to simulate the
evolution of the low-earth orbit environment, enhancing the MIT Orbital
Capacity Analysis Tool (MOCAT). In recent decades, numerous space environment
models have been developed by government agencies and research groups to
understand and predict the dynamics of space debris. Our MC approach advances
this by simulating the trajectories of space objects and modeling their
interactions, such as collisions and explosions. This aids in analyzing the
trends of space-object and debris populations. A key innovation of our method
is the computational efficiency in orbit propagation, which is crucial for
handling potentially large numbers of objects over centuries. We present
validation results against the IADC (Inter-Agency Space Debris Coordination
Committee) study and explore various scenarios, including ones without future
launches and those involving the launch of proposed megaconstellations with
over 80,000 active payloads. With the improvement in computational efficiencies
provided by this work, we can run these new scenarios that predict millions of
trackable objects over a 200-year period. The previous state-of-the-art was
400,000 objects over the same period of time. Notably, while fewer
megaconstellations are planned for altitudes above 800 km, even minimal
failures in post-mission disposal or collision avoidance maneuvers can
significantly impact orbital debris accumulation.
