Gravity
The simulator applies Newtonian point-mass acceleration: a = G·M·r̂/r². The code scales the displacement vector by G·M/r³ so direction and magnitude stay coupled.
Model notes
Physics stays in SI units.
Every body stores mass in kilograms, radius in meters, positions in meters, velocities in meters per second, and acceleration in meters per second squared.
Integration
The physics step uses velocity-Verlet: half-kick velocity, drift position, recompute acceleration, then finish the second half-kick.
Initial orbits
Planets and moons start from perihelion, perigee, or periareion assumptions with vis-viva speeds relative to their parent frame.