nyx_space/dynamics/
solarpressure.rs

1/*
2    Nyx, blazing fast astrodynamics
3    Copyright (C) 2018-onwards Christopher Rabotin <christopher.rabotin@gmail.com>
4
5    This program is free software: you can redistribute it and/or modify
6    it under the terms of the GNU Affero General Public License as published
7    by the Free Software Foundation, either version 3 of the License, or
8    (at your option) any later version.
9
10    This program is distributed in the hope that it will be useful,
11    but WITHOUT ANY WARRANTY; without even the implied warranty of
12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13    GNU Affero General Public License for more details.
14
15    You should have received a copy of the GNU Affero General Public License
16    along with this program.  If not, see <https://www.gnu.org/licenses/>.
17*/
18
19use super::{DynamicsAlmanacSnafu, DynamicsError, DynamicsPlanetarySnafu, ForceModel};
20use crate::cosmic::eclipse::ShadowModel;
21use crate::cosmic::{AU, Frame, SPEED_OF_LIGHT_M_S, Spacecraft};
22use crate::linalg::{Const, Matrix4x3, Vector3};
23use anise::almanac::Almanac;
24use anise::constants::frames::{EARTH_J2000, SUN_J2000};
25use hyperdual::{Float, OHyperdual, hyperspace_from_vector, linalg::norm};
26use log::warn;
27use serde::{Deserialize, Serialize};
28use serde_dhall::StaticType;
29use snafu::ResultExt;
30use std::fmt;
31use std::sync::Arc;
32
33// Default solar flux in W/m^2
34#[allow(non_upper_case_globals)]
35pub const SOLAR_FLUX_W_m2: f64 = 1367.0;
36
37#[cfg(feature = "python")]
38use pyo3::prelude::*;
39
40/// Computation of solar radiation pressure is based on STK: <http://help.agi.com/stk/index.htm#gator/eq-solar.htm> .
41#[derive(Clone, Debug, Serialize, Deserialize, StaticType)]
42#[cfg_attr(feature = "python", pyclass(from_py_object, get_all, set_all))]
43pub struct SolarPressure {
44    /// solar flux at 1 AU, in W/m^2
45    pub phi: f64,
46    pub shadow_model: ShadowModel,
47    /// Set to true to estimate the coefficient of reflectivity
48    pub estimate: bool,
49}
50
51impl Default for SolarPressure {
52    /// Important: the default will FAIL at runtime if the shadow model is not manually defined with loaded frames.
53    fn default() -> Self {
54        Self {
55            phi: SOLAR_FLUX_W_m2,
56            estimate: false,
57            shadow_model: ShadowModel {
58                light_source: SUN_J2000,
59                shadow_bodies: vec![EARTH_J2000],
60            },
61        }
62    }
63}
64
65impl SolarPressure {
66    /// Will set the solar flux at 1 AU to: Phi = 1367.0
67    pub fn default_flux_raw(
68        shadow_bodies: Vec<Frame>,
69        almanac: &Almanac,
70    ) -> Result<Self, DynamicsError> {
71        let shadow_model = ShadowModel {
72            light_source: almanac.frame_info(SUN_J2000).context({
73                DynamicsPlanetarySnafu {
74                    action: "planetary data from third body not loaded",
75                }
76            })?,
77            shadow_bodies: shadow_bodies
78                .iter()
79                .filter_map(|object| match almanac.frame_info(object) {
80                    Ok(loaded_obj) => Some(loaded_obj),
81                    Err(e) => {
82                        warn!("when initializing SRP model for {object}, {e}");
83                        None
84                    }
85                })
86                .collect(),
87        };
88        Ok(Self {
89            phi: SOLAR_FLUX_W_m2,
90            shadow_model,
91            estimate: true,
92        })
93    }
94
95    /// Accounts for the shadowing of only one body and will set the solar flux at 1 AU to: Phi = 1367.0
96    pub fn default_flux(shadow_body: Frame, almanac: &Almanac) -> Result<Arc<Self>, DynamicsError> {
97        Ok(Arc::new(Self::default_flux_raw(
98            vec![shadow_body],
99            almanac,
100        )?))
101    }
102
103    /// Accounts for the shadowing of only one body and will set the solar flux at 1 AU to: Phi = 1367.0
104    pub fn default_no_estimation(
105        shadow_bodies: Vec<Frame>,
106        almanac: &Almanac,
107    ) -> Result<Arc<Self>, DynamicsError> {
108        let mut srp = Self::default_flux_raw(shadow_bodies, almanac)?;
109        srp.estimate = false;
110        Ok(Arc::new(srp))
111    }
112
113    /// Must provide the flux in W/m^2
114    pub fn with_flux(
115        flux_w_m2: f64,
116        shadow_bodies: Vec<Frame>,
117        almanac: &Almanac,
118    ) -> Result<Arc<Self>, DynamicsError> {
119        let mut me = Self::default_flux_raw(shadow_bodies, almanac)?;
120        me.phi = flux_w_m2;
121        Ok(Arc::new(me))
122    }
123
124    /// Solar radiation pressure force model accounting for the provided shadow bodies.
125    pub fn new(shadow_bodies: Vec<Frame>, almanac: &Almanac) -> Result<Arc<Self>, DynamicsError> {
126        Ok(Arc::new(Self::default_flux_raw(shadow_bodies, almanac)?))
127    }
128}
129
130impl ForceModel for SolarPressure {
131    fn estimation_index(&self) -> Option<usize> {
132        if self.estimate { Some(6) } else { None }
133    }
134
135    fn eom(&self, ctx: &Spacecraft, almanac: &Almanac) -> Result<Vector3<f64>, DynamicsError> {
136        let osc = ctx.orbit;
137        // Compute the position of the Sun as seen from the spacecraft
138        let r_sun = almanac
139            .transform_to(ctx.orbit, self.shadow_model.light_source, None)
140            .context(DynamicsAlmanacSnafu {
141                action: "transforming state to vector seen from Sun",
142            })?
143            .radius_km;
144
145        let r_sun_unit = r_sun / r_sun.norm();
146
147        // ANISE returns the occultation percentage (or factor), which is the opposite as the illumination factor.
148        let occult = self
149            .shadow_model
150            .compute(osc, almanac)
151            .context(DynamicsAlmanacSnafu {
152                action: "solar radiation pressure computation",
153            })?
154            .factor();
155
156        // Compute the illumination factor.
157        let k: f64 = (occult - 1.0).abs();
158
159        let r_sun_au = r_sun.norm() / AU;
160        // in N/(m^2)
161        let flux_pressure = (k * self.phi / SPEED_OF_LIGHT_M_S) * (1.0 / r_sun_au).powi(2);
162
163        // Note the 1e-3 is to convert the SRP from m/s^2 to km/s^2
164        Ok(1e-3 * ctx.srp.coeff_reflectivity * ctx.srp.area_m2 * flux_pressure * r_sun_unit)
165    }
166
167    fn gradient(
168        &self,
169        ctx: &Spacecraft,
170        almanac: &Almanac,
171    ) -> Result<(Vector3<f64>, Matrix4x3<f64>), DynamicsError> {
172        let osc = ctx.orbit;
173
174        // Compute the position of the Sun as seen from the spacecraft
175        let r_sun = almanac
176            .transform_to(ctx.orbit, self.shadow_model.light_source, None)
177            .context(DynamicsAlmanacSnafu {
178                action: "transforming state to vector seen from Sun",
179            })?
180            .radius_km;
181
182        let r_sun_d: Vector3<OHyperdual<f64, Const<9>>> = hyperspace_from_vector(&r_sun);
183        let r_sun_unit = r_sun_d / norm(&r_sun_d);
184
185        // ANISE returns the occultation percentage (or factor), which is the opposite as the illumination factor.
186        let occult = self
187            .shadow_model
188            .compute(osc, almanac)
189            .context(DynamicsAlmanacSnafu {
190                action: "solar radiation pressure computation",
191            })?
192            .factor();
193
194        // Compute the illumination factor.
195        let k: f64 = (occult - 1.0).abs();
196
197        let r_sun_au = norm(&r_sun_d) / AU;
198        let inv_r_sun_au = OHyperdual::<f64, Const<9>>::from_real(1.0) / (r_sun_au);
199        let inv_r_sun_au_p2 = inv_r_sun_au.powi(2);
200        // in N/(m^2)
201        let flux_pressure =
202            OHyperdual::<f64, Const<9>>::from_real(k * self.phi / SPEED_OF_LIGHT_M_S)
203                * inv_r_sun_au_p2;
204
205        // Note the 1e-3 is to convert the SRP from m/s^2 to km/s^2
206        let dual_force_scalar = OHyperdual::<f64, Const<9>>::from_real(
207            1e-3 * ctx.srp.coeff_reflectivity * ctx.srp.area_m2,
208        );
209        let mut dual_force: Vector3<OHyperdual<f64, Const<9>>> = Vector3::zeros();
210        dual_force[0] = dual_force_scalar * flux_pressure * r_sun_unit[0];
211        dual_force[1] = dual_force_scalar * flux_pressure * r_sun_unit[1];
212        dual_force[2] = dual_force_scalar * flux_pressure * r_sun_unit[2];
213
214        // Extract result into Vector6 and Matrix6
215        let mut dx = Vector3::zeros();
216        let mut grad = Matrix4x3::zeros();
217        for i in 0..3 {
218            dx[i] += dual_force[i].real();
219            // NOTE: Although the hyperdual state is of size 7, we're only setting the values up to 3 (Matrix3)
220            for j in 0..3 {
221                grad[(i, j)] += dual_force[i][j + 1];
222            }
223        }
224
225        // Compute the partial wrt to Cr.
226        let wrt_cr = self.eom(ctx, almanac)? / ctx.srp.coeff_reflectivity;
227        for j in 0..3 {
228            grad[(3, j)] = wrt_cr[j];
229        }
230
231        Ok((dx, grad))
232    }
233}
234
235impl fmt::Display for SolarPressure {
236    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
237        write!(
238            f,
239            "SRP with φ = {} W/m^2 and eclipse {}",
240            self.phi, self.shadow_model
241        )
242    }
243}
244
245#[cfg(feature = "python")]
246#[cfg_attr(feature = "python", pymethods)]
247impl SolarPressure {
248    #[pyo3(signature = (shadow_bodies, almanac, flux_w_m2=SOLAR_FLUX_W_m2, estimate=true))]
249    #[new]
250    fn py_new(
251        shadow_bodies: Vec<Frame>,
252        almanac: &Almanac,
253        flux_w_m2: f64,
254        estimate: bool,
255    ) -> Result<Self, DynamicsError> {
256        let mut me = Self::default_flux_raw(shadow_bodies, almanac)?;
257        me.phi = flux_w_m2;
258        me.estimate = estimate;
259
260        Ok(me)
261    }
262
263    fn __str__(&self) -> String {
264        format!("{self}")
265    }
266
267    fn __repr__(&self) -> String {
268        format!("{self} @ {self:p}")
269    }
270}
nyx_space/dynamics/solarpressure.rs

nyx_space/dynamics/
solarpressure.rs
