principia

Typed Newtonian numerical dynamics for Rust: state propagation, acceleration-model composition, RK4 / DOPRI5 / DOP853 integrators, variational equations / STM, covariance transport, local trajectory frames, and gravity-field kernels.

principia is the numerical companion to keplerian (analytic Kepler / conic mechanics). Both build on the typed primitives in qtty, affn, and tempoch.

Layering

qtty + affn + tempoch
        |
        +--> keplerian   # analytic Kepler / conic mechanics
        |
        +--> principia   # numerical Newtonian dynamics + propagation
                    |
                    +--> siderust   # astronomy/geodesy adapters
                                    # (ephemerides, EOP, atmospheres, ...)

principia depends only on qtty, affn, tempoch, and thiserror (plus optional serde). It does not depend on siderust, keplerian, cheby, ephemerides, Earth orientation data, observatory/atmosphere policy, or any adapter / dataset crate. Astronomy specifics live downstream in siderust::astro::perturbations.

principia and keplerian deliberately overlap on two-body arithmetic: keplerian is the analytic closed-form path, principia is the numerical integration path. There is no runtime principia -> keplerian dependency.

Public vocabulary

principia uses generic mechanics vocabulary rather than astronomy specific names:

Concept	Type
Cartesian state	DynamicsState<S, C, F>
State time derivative	StateDerivative<F>
Acceleration model trait	AccelerationModel<Ctx, S, C, F>
Acceleration Jacobian blocks	AccelerationPartials<F>
Composite model	CompositeModel<…>
Local trajectory frame	LocalTrajectoryFrame + RTN / VNC / LVLH
Crate-level error	PrincipiaError

Time is carried as a tempoch::Time<S> parameterized by the continuous time scale S. Propagation accepts typed qtty::Second steps. The mechanics kernel never performs time-scale conversion — downstream adapters provide states and contexts already on the intended scale.

Features

• default = ["std"]
• std / alloc — standard / allocator support
• serde — derives for stable public data types
• astro — optional convenience aliases over affn astronomical frame markers. Does not pull in Earth/Sun/Moon constants, ephemerides, observatory/atmosphere policy, or any astronomy provider.

License

AGPL-3.0-only. See LICENSE.