Newtonian core

Simulation state uses physical units first.

The simulator treats rendering as a view of SI-unit state. This page names the assumptions that make the current model readable and testable.

Core equation

a = G * source_mass / distance^3 * displacement

The implementation scales the displacement vector directly, so direction and magnitude remain coupled in src/sim/physics.c.

Source-backed model facts

src/sim/vec3d.c provides double-precision vector operations.
src/sim/body.c stores mass, radius, position, velocity, and acceleration in SI units.
src/sim/physics.c computes Newtonian point-mass acceleration.
src/sim/solar_system.c initializes the Sun, planets, Moon, Phobos, and Deimos with parent-aware states.
The integrator is velocity-Verlet / kick-drift-kick, not Euler stepping.

Known approximations

The Sun remains fixed for the current milestone. The project does not claim relativistic precession, J2000 state vectors, barycentric Earth-Moon initialization, or ephemeris accuracy.

That limitation is intentional for the foundation: the goal is inspectable orbital mechanics before catalog scale.