Crate tpt_sci_astro 

tpt-sci-astro

Orbital-mechanics and coordinate-frame primitives for the tpt-science pillar, built entirely from scratch on top of the in-house tpt-math-linalg dense linear algebra (no external astrodynamics or geometry wrappers).

The crate implements the classical two-body problem in an Earth-Centered Inertial (ECI) reference frame:

• Classical (Keplerian) OrbitalElements, validated on construction.
• Conversion between Keplerian elements and ECI Cartesian state vectors (OrbitalElements::state_vector and OrbitalElements::from_state).
• Time propagation via Kepler’s equation (state -> mean anomaly -> advance -> solve -> true anomaly) in OrbitalElements::propagate.
• First-order secular J₂ perturbation: OrbitalElements::propagate_j2 and OrbitalElements::j2_secular_rates give the dominant long-term nodal regression and apsidal precession for oblate-body missions (e.g. sun-synchronous orbit design). OrbitalElements::propagate_j4 / OrbitalElements::j4_secular_rates extend this with the J₄ zonal term.
• Atmospheric drag: atmospheric_density (single-band exponential model) and OrbitalElements::propagate_drag / OrbitalElements::drag_da_dt for secular along-track decay.
• Simplified (Kozai-Lidov, quadrupole-order) third-body secular perturbation: OrbitalElements::third_body_secular_rates / OrbitalElements::propagate_third_body.
• Cannonball solar radiation pressure with a cylindrical Earth-shadow eclipse test: srp_acceleration, in_earth_shadow, OrbitalElements::srp_acceleration_vector.

All angles are in radians. The model assumes an ideal point-mass central body for the pure two-body propagation; each perturbation above is an independent first-order secular add-on (not a combined integrated force model), so short-periodic oscillations are not captured and the perturbations are not accumulated together automatically.

Examples

use tpt_math_linalg::tpt_math_linalg_dense::{DVector, DMatrix};
use tpt_sci_astro::OrbitalElements;

// A unit circular orbit about a unit-mass body.
let el = OrbitalElements::new(1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0).unwrap();
let (r, _v) = el.state_vector();
assert!((r.norm() - 1.0).abs() < 1e-9);

Licensed under either of MIT or Apache-2.0 at your option.

Structs

OrbitalElements

A classical (Keplerian) set of orbital elements describing an elliptical orbit in an Earth-Centered Inertial (ECI) frame.

Enums

AstroError

Errors produced by the astrodynamics primitives.

Constants

ASTRONOMICAL_UNIT_KM

One astronomical unit, in km.

EARTH_ATM_H0_KM

Reference altitude (km) for EARTH_ATM_RHO0_KG_M3 / EARTH_ATM_SCALE_HEIGHT_KM.

EARTH_ATM_RHO0_KG_M3

Reference atmospheric density (kg/m³) for the single-band exponential Earth atmosphere model, evaluated at EARTH_ATM_H0_KM.

EARTH_ATM_SCALE_HEIGHT_KM

Atmospheric scale height (km) for the ~400 km exponential density band (see EARTH_ATM_RHO0_KG_M3).

EARTH_J2

Earth’s second zonal harmonic J₂ (dimensionless), the leading oblateness term that drives nodal regression and apsidal precession.

EARTH_J4

Earth’s fourth zonal harmonic J₄ (dimensionless), the next zonal oblateness term after J₂.

EARTH_MU

Gravitational parameter of the Earth, μ = GM, in km³·s⁻².

EARTH_RADIUS_EQ

Earth’s equatorial radius Rₑ in km, the reference length for the J₂ perturbation (the perturbation scales as (Rₑ/p)²).

MOON_DISTANCE_KM

Mean Earth-Moon distance, in km.

MOON_MU

Gravitational parameter of the Moon, μ_Moon = GM_Moon, in km³·s⁻².

SOLAR_PRESSURE_1AU

Solar radiation pressure at 1 AU, in N/m² (solar constant / speed of light, ≈ 1361 W/m² / 2.998e8 m/s).

SUN_MU

Gravitational parameter of the Sun, μ☉ = GM☉, in km³·s⁻².

Functions

atmospheric_density

Exponential atmospheric density model, ρ(h) = ρ0 · exp(-(h - h0) / H).

cross3

Cross product of two 3-vectors, a × b.

eccentric_to_true

Convert an eccentric anomaly E to a true anomaly nu for eccentricity e.

in_earth_shadow

Cylindrical Earth-shadow (eclipse) test.

perifocal_to_eci

The 3×3 rotation matrix Q that maps perifocal-frame coordinates to ECI.

solve_kepler

Solve Kepler’s equation M = E - e·sin(E) for E via Newton iteration.

srp_acceleration

Cannonball-model solar radiation pressure acceleration magnitude, in km/s².

true_to_eccentric

Convert a true anomaly nu to an eccentric anomaly E for eccentricity e.