marss 0.0.3

Mars celestial simulation crate for the MilkyWay SolarSystem workspace
Documentation 
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use sciforge::hub::domain::common::constants::G;

pub const DEIMOS_MASS: f64 = 1.4762e15;
pub const DEIMOS_RADIUS: f64 = 6_200.0;
pub const DEIMOS_DIMENSIONS: (f64, f64, f64) = (15_000.0, 12_200.0, 10_400.0);
pub const DEIMOS_SEMI_MAJOR_AXIS: f64 = 23_463_200.0;
pub const DEIMOS_ECCENTRICITY: f64 = 0.00033;
pub const DEIMOS_INCLINATION_DEG: f64 = 0.93;
pub const DEIMOS_ORBITAL_PERIOD_S: f64 = 109_075.0;
pub const DEIMOS_DENSITY: f64 = 1_471.0;
pub const DEIMOS_ALBEDO: f64 = 0.068;
pub const DEIMOS_SURFACE_GRAVITY: f64 = 0.003;

pub struct DeimosState {
    pub mass_kg: f64,
    pub semi_major_axis_m: f64,
    pub eccentricity: f64,
    pub inclination_rad: f64,
    pub mean_anomaly_rad: f64,
}

impl Default for DeimosState {
    fn default() -> Self {
        Self::new()
    }
}

impl DeimosState {
    pub fn new() -> Self {
        Self {
            mass_kg: DEIMOS_MASS,
            semi_major_axis_m: DEIMOS_SEMI_MAJOR_AXIS,
            eccentricity: DEIMOS_ECCENTRICITY,
            inclination_rad: DEIMOS_INCLINATION_DEG.to_radians(),
            mean_anomaly_rad: 0.0,
        }
    }

    pub fn orbital_period_s(&self) -> f64 {
        let mu = G * crate::MARS_MASS;
        2.0 * std::f64::consts::PI * (self.semi_major_axis_m.powi(3) / mu).sqrt()
    }

    pub fn orbital_velocity_ms(&self) -> f64 {
        (G * crate::MARS_MASS / self.semi_major_axis_m).sqrt()
    }

    pub fn step(&mut self, dt_s: f64) {
        let n = 2.0 * std::f64::consts::PI / self.orbital_period_s();
        self.mean_anomaly_rad = (self.mean_anomaly_rad + n * dt_s) % (2.0 * std::f64::consts::PI);
    }

    fn eccentric_anomaly(&self) -> f64 {
        let m = self.mean_anomaly_rad;
        let e = self.eccentricity;
        let mut ea = m + e * m.sin();
        for _ in 0..15 {
            let f = ea - e * ea.sin() - m;
            let fp = 1.0 - e * ea.cos();
            ea -= f / fp;
        }
        ea
    }

    fn true_anomaly(&self) -> f64 {
        let ea = self.eccentric_anomaly();
        let e = self.eccentricity;
        2.0 * f64::atan2(
            (1.0 + e).sqrt() * (ea / 2.0).sin(),
            (1.0 - e).sqrt() * (ea / 2.0).cos(),
        )
    }

    pub fn distance(&self) -> f64 {
        let nu = self.true_anomaly();
        let e = self.eccentricity;
        self.semi_major_axis_m * (1.0 - e * e) / (1.0 + e * nu.cos())
    }

    pub fn escape_velocity(&self) -> f64 {
        (2.0 * G * DEIMOS_MASS / DEIMOS_RADIUS).sqrt()
    }
}

pub fn orbital_expansion_rate_m_per_year() -> f64 {
    2.4e-3
}

pub fn apparent_angular_size_rad() -> f64 {
    use sciforge::hub::domain::astronomy::celestial::apparent_angular_size;
    apparent_angular_size(DEIMOS_RADIUS, DEIMOS_SEMI_MAJOR_AXIS - crate::MARS_RADIUS)
}

pub fn solar_transit_duration_s() -> f64 {
    120.0
}