50 lines
1.9 KiB
Rust
50 lines
1.9 KiB
Rust
//! Keplerian orbital elements and two-body propagation.
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//!
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//! A Keplerian element set describes an orbit as an ellipse, a parabola, or
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//! a hyperbola with a fixed orientation in space. From the six elements and
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//! the gravitational parameter, this crate computes the position and
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//! velocity at any time under the two-body assumption, and converts in the
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//! other direction.
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//!
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//! The two-body model includes only the point mass gravity of the central
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//! body. It omits the oblateness of the Earth, drag, and third body
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//! perturbations, so it drifts from reality over time. It is the right model
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//! for analysing an orbit whose elements are already known, for example to
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//! find the radius at a true anomaly, and the wrong model for propagating a
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//! two-line element set, which is the job of `apsis-sgp4`.
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//!
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//! Angles are in radians. Lengths are kilometers and the gravitational
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//! parameter is in cubic kilometers per second squared, matching the rest of
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//! the orbit layer.
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//!
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//! ```
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//! use apsis_kepler::{GravityParameter, KeplerianElements};
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//!
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//! // A circular orbit at the Earth's equatorial radius has the speed
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//! // sqrt(mu / r), about 7.9 km/s.
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//! let elements = KeplerianElements {
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//! semi_major_axis: 6_378.137,
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//! eccentricity: 0.0,
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//! inclination: 0.0,
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//! right_ascension: 0.0,
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//! argument_of_perigee: 0.0,
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//! true_anomaly: 0.0,
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//! };
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//! let state = elements.to_state(GravityParameter::WGS84).expect("valid elements");
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//! assert!((state.velocity.norm() - 7.909).abs() < 0.01);
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//! ```
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#![forbid(unsafe_code)]
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#![deny(missing_docs)]
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mod anomaly;
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mod elements;
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mod parameter;
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pub use anomaly::{
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eccentric_from_mean, eccentric_from_true, mean_from_eccentric, mean_from_true,
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true_from_eccentric, true_from_mean, wrap_to_pi,
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};
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pub use elements::{KeplerianElements, State, perifocal_to_inertial};
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pub use parameter::GravityParameter;
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