Force Models¶

use brahe as bh;
use bh::GravityModelType;

fn main() {

    // Create a fully-configured force model
    let force_config = bh::ForceModelConfig {
        // Gravity: Spherical harmonic model (EGM2008, 20x20 degree/order)
        gravity: bh::GravityConfiguration::SphericalHarmonic {
            source: bh::GravityModelSource::ModelType(GravityModelType::EGM2008_360),
            degree: 20,
            order: 20,
        },
        // Atmospheric drag: Harris-Priester model with parameter indices
        drag: Some(bh::DragConfiguration {
            model: bh::AtmosphericModel::HarrisPriester,
            area: bh::ParameterSource::ParameterIndex(1), // Index into parameter vector
            cd: bh::ParameterSource::ParameterIndex(2),
        }),
        // Solar radiation pressure: Conical eclipse model
        srp: Some(bh::SolarRadiationPressureConfiguration {
            area: bh::ParameterSource::ParameterIndex(3),
            cr: bh::ParameterSource::ParameterIndex(4),
            eclipse_model: bh::EclipseModel::Conical,
        }),
        // Third-body: Sun and Moon with DE440s ephemeris
        third_body: Some(bh::ThirdBodyConfiguration {
            ephemeris_source: bh::EphemerisSource::DE440s,
            bodies: vec![bh::ThirdBody::Sun, bh::ThirdBody::Moon],
        }),
        // General relativistic corrections
        relativity: true,
        // Spacecraft mass (can also use ParameterIndex for estimation)
        mass: Some(bh::ParameterSource::Value(1000.0)), // kg
        // ECI<->ECEF rotation precision used by gravity, drag, and density models.
        // FullEarthRotation is the default and applies the full IAU 2006/2000A
        // bias-precession-nutation + Earth rotation + polar motion. Use
        // EarthRotationOnly for a faster, slightly less accurate alternative.
        frame_transform: bh::FrameTransformationModel::FullEarthRotation,
    };

    println!("Gravity: {:?}", force_config.gravity);
    println!("Drag: {:?}", force_config.drag);
    println!("SRP: {:?}", force_config.srp);
    println!("Third-body: {:?}", force_config.third_body);
    println!("Relativity: {:?}", force_config.relativity);
    println!("Mass: {:?}", force_config.mass);
    println!("Frame transform: {:?}", force_config.frame_transform);
}

use brahe as bh;

fn main() {
    // Point mass gravity configuration
    // Uses only central body gravity (mu/r^2)
    // No spherical harmonics, J2, or higher-order terms
    let _force_config = bh::ForceModelConfig {
        gravity: bh::GravityConfiguration::PointMass,
        drag: None,
        srp: None,
        third_body: None,
        relativity: false,
        mass: None,
        frame_transform: bh::FrameTransformationModel::default(),
    };
}

use brahe as bh;
use bh::GravityModelType;

fn main() {
    // ==========================================================================
    // Packaged Gravity Models
    // ==========================================================================

    // EGM2008 - High-fidelity NGA model (360x360 max)
    let _gravity_egm2008 = bh::GravityConfiguration::SphericalHarmonic {
        source: bh::GravityModelSource::ModelType(GravityModelType::EGM2008_360),
        degree: 20,
        order: 20,
    };

    // GGM05S - GRACE mission model (180x180 max)
    let _gravity_ggm05s = bh::GravityConfiguration::SphericalHarmonic {
        source: bh::GravityModelSource::ModelType(GravityModelType::GGM05S),
        degree: 20,
        order: 20,
    };

    // JGM3 - Legacy model, fast computation (70x70 max)
    let _gravity_jgm3 = bh::GravityConfiguration::SphericalHarmonic {
        source: bh::GravityModelSource::ModelType(GravityModelType::JGM3),
        degree: 20,
        order: 20,
    };

    // ==========================================================================
    // Custom Model from File
    // ==========================================================================

    // Load custom gravity model from GFC format file
    // GravityModelType::from_file validates the path exists
    let custom_model_type =
        GravityModelType::from_file("data/gravity_models/EGM2008_360.gfc").unwrap();
    let _gravity_custom = bh::GravityConfiguration::SphericalHarmonic {
        source: bh::GravityModelSource::ModelType(custom_model_type),
        degree: 20,
        order: 20,
    };
}

use brahe as bh;
use bh::GravityModelType;
use bh::datasets::icgem::ICGEMBody;

fn main() {
    // Reference an ICGEM Earth model. Use
    // `bh::datasets::icgem::list_icgem_models(ICGEMBody::Earth)` to discover
    // the full catalog. Append "-<DEGREE>" to pin a specific variant.
    let grav_type = GravityModelType::ICGEMModel {
        body: ICGEMBody::Earth,
        name: "JGM3".to_string(),
    };

    let _force_config = bh::ForceModelConfig {
        gravity: bh::GravityConfiguration::SphericalHarmonic {
            source: bh::GravityModelSource::ModelType(grav_type),
            degree: 20,
            order: 20,
        },
        drag: None,
        srp: None,
        third_body: None,
        relativity: false,
        mass: None,
        frame_transform: bh::FrameTransformationModel::default(),
    };

    println!("Built ForceModelConfig with ICGEM gravity source: Earth/JGM3 (20x20)");
}

use brahe as bh;

fn main() {
    // Harris-Priester atmospheric drag configuration
    // - Valid for altitudes 100-1000 km
    // - Accounts for latitude-dependent diurnal bulge
    // - Does not require space weather data (F10.7, Ap)

    // Using parameter indices (default layout)
    let _drag_config = bh::DragConfiguration {
        model: bh::AtmosphericModel::HarrisPriester,
        area: bh::ParameterSource::ParameterIndex(1), // drag_area from params[1]
        cd: bh::ParameterSource::ParameterIndex(2),   // Cd from params[2]
    };
}

use brahe as bh;

fn main() {
    // Initialize space weather data provider
    bh::initialize_sw().unwrap();

    // NRLMSISE-00 atmospheric drag configuration
    // - Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar
    // - High-fidelity empirical model
    // - Valid from ground to thermospheric heights
    // - Uses space weather data (F10.7, Ap) when available
    // - More computationally expensive than Harris-Priester

    let _drag_config = bh::DragConfiguration {
        model: bh::AtmosphericModel::NRLMSISE00,
        area: bh::ParameterSource::ParameterIndex(1), // drag_area from params[1]
        cd: bh::ParameterSource::ParameterIndex(2),   // Cd from params[2]
    };
}

use brahe as bh;
use bh::GravityModelType;

fn main() {

    let drag_config = bh::DragConfiguration {
        model: bh::AtmosphericModel::Exponential {
            scale_height: 53000.0, // Scale height H in meters (53 km for ~300 km altitude)
            rho0: 1.225e-11,       // Reference density at h0 in kg/m^3
            h0: 300000.0,          // Reference altitude in meters (300 km)
        },
        area: bh::ParameterSource::ParameterIndex(1),
        cd: bh::ParameterSource::ParameterIndex(2),
    };

    // Create force model with exponential drag
    let _force_config = bh::ForceModelConfig {
        gravity: bh::GravityConfiguration::SphericalHarmonic {
            source: bh::GravityModelSource::ModelType(GravityModelType::EGM2008_360),
            degree: 20,
            order: 20,
        },
        drag: Some(drag_config),
        srp: None,
        third_body: None,
        relativity: false,
        mass: Some(bh::ParameterSource::ParameterIndex(0)),
        frame_transform: bh::FrameTransformationModel::default(),
    };
}

use brahe as bh;

fn main() {
    // Solar Radiation Pressure configuration
    // Parameters:
    // - area: Cross-sectional area facing the Sun (m^2)
    // - cr: Coefficient of reflectivity (1.0=absorbing to 2.0=perfectly reflecting)
    // - eclipse_model: How to handle Earth's shadow

    // Option 1: No eclipse model (always illuminated)
    // Fast but inaccurate during eclipse periods
    let _srp_no_eclipse = bh::SolarRadiationPressureConfiguration {
        area: bh::ParameterSource::ParameterIndex(3), // srp_area from params[3]
        cr: bh::ParameterSource::ParameterIndex(4),   // Cr from params[4]
        eclipse_model: bh::EclipseModel::None,
    };

    // Option 2: Cylindrical shadow model
    // Simple and fast, sharp shadow boundary (no penumbra)
    let _srp_cylindrical = bh::SolarRadiationPressureConfiguration {
        area: bh::ParameterSource::ParameterIndex(3),
        cr: bh::ParameterSource::ParameterIndex(4),
        eclipse_model: bh::EclipseModel::Cylindrical,
    };

    // Option 3: Conical shadow model (recommended)
    // Accounts for penumbra and umbra regions
    let _srp_conical = bh::SolarRadiationPressureConfiguration {
        area: bh::ParameterSource::ParameterIndex(3),
        cr: bh::ParameterSource::ParameterIndex(4),
        eclipse_model: bh::EclipseModel::Conical,
    };
}

use brahe as bh;
use bh::GravityModelType;

fn main() {
    // Third-body perturbations configuration
    // Gravitational attraction from other celestial bodies

    // Option 1: Low-precision analytical ephemerides
    // Fast but less accurate (~km level errors for Sun/Moon)
    // Only Sun and Moon are available
    let _third_body_low = bh::ThirdBodyConfiguration {
        ephemeris_source: bh::EphemerisSource::LowPrecision,
        bodies: vec![bh::ThirdBody::Sun, bh::ThirdBody::Moon],
    };

    // Option 2: DE440s high-precision ephemerides (recommended)
    // Uses JPL Development Ephemeris 440 (small bodies version)
    // ~m level accuracy, valid 1550-2650 CE
    // All planets available, ~17 MB file
    let third_body_de440s = bh::ThirdBodyConfiguration {
        ephemeris_source: bh::EphemerisSource::DE440s,
        bodies: vec![bh::ThirdBody::Sun, bh::ThirdBody::Moon],
    };

    // Option 3: DE440 full-precision ephemerides
    // Highest accuracy (~mm level), valid 13200 BCE-17191 CE
    // All planets available, ~114 MB file
    let _third_body_de440 = bh::ThirdBodyConfiguration {
        ephemeris_source: bh::EphemerisSource::DE440,
        bodies: vec![bh::ThirdBody::Sun, bh::ThirdBody::Moon],
    };

    // Option 4: Include all major planets (high-fidelity)
    let _third_body_all_planets = bh::ThirdBodyConfiguration {
        ephemeris_source: bh::EphemerisSource::DE440s,
        bodies: vec![
            bh::ThirdBody::Sun,
            bh::ThirdBody::Moon,
            bh::ThirdBody::Mercury,
            bh::ThirdBody::Venus,
            bh::ThirdBody::Mars,
            bh::ThirdBody::Jupiter,
            bh::ThirdBody::Saturn,
            bh::ThirdBody::Uranus,
            bh::ThirdBody::Neptune,
        ],
    };

    // Create force model with Sun/Moon perturbations (common case)
    let _force_config = bh::ForceModelConfig {
        gravity: bh::GravityConfiguration::SphericalHarmonic {
            source: bh::GravityModelSource::ModelType(GravityModelType::EGM2008_360),
            degree: 20,
            order: 20,
        },
        drag: None,
        srp: None,
        third_body: Some(third_body_de440s),
        relativity: false,
        mass: None,
        frame_transform: bh::FrameTransformationModel::default(),
    };
}

use brahe as bh;
use bh::GravityModelType;

fn main() {
    // ParameterSource::Value creates a fixed constant parameter
    // Use when the parameter doesn't change and doesn't need to be estimated

    // Example: Fixed drag configuration
    // Mass, drag area, and Cd are all constant
    let drag_config = bh::DragConfiguration {
        model: bh::AtmosphericModel::HarrisPriester,
        area: bh::ParameterSource::Value(10.0), // Fixed 10 m^2 drag area
        cd: bh::ParameterSource::Value(2.2),    // Fixed Cd of 2.2
    };

    // Example: Fixed SRP configuration
    let srp_config = bh::SolarRadiationPressureConfiguration {
        area: bh::ParameterSource::Value(15.0), // Fixed 15 m^2 SRP area
        cr: bh::ParameterSource::Value(1.3),    // Fixed Cr of 1.3
        eclipse_model: bh::EclipseModel::Conical,
    };

    // Create force model with all fixed parameters
    let _force_config = bh::ForceModelConfig {
        gravity: bh::GravityConfiguration::SphericalHarmonic {
            source: bh::GravityModelSource::ModelType(GravityModelType::EGM2008_360),
            degree: 20,
            order: 20,
        },
        drag: Some(drag_config),
        srp: Some(srp_config),
        third_body: Some(bh::ThirdBodyConfiguration {
            ephemeris_source: bh::EphemerisSource::LowPrecision,
            bodies: vec![bh::ThirdBody::Sun, bh::ThirdBody::Moon],
        }),
        relativity: false,
        mass: Some(bh::ParameterSource::Value(500.0)), // Fixed 500 kg mass
        frame_transform: bh::FrameTransformationModel::default(),
    };
}

use brahe as bh;

fn main() {
    // ParameterSource::ParameterIndex references a value in the parameter vector
    // Use when parameters may change or need to be estimated

    // Default parameter layout:
    // Index 0: mass (kg)
    // Index 1: drag_area (m^2)
    // Index 2: Cd (dimensionless)
    // Index 3: srp_area (m^2)
    // Index 4: Cr (dimensionless)

    let _drag_config = bh::DragConfiguration {
        model: bh::AtmosphericModel::HarrisPriester,
        area: bh::ParameterSource::ParameterIndex(1), // params[1] = drag_area
        cd: bh::ParameterSource::ParameterIndex(2),   // params[2] = Cd
    };

    let _srp_config = bh::SolarRadiationPressureConfiguration {
        area: bh::ParameterSource::ParameterIndex(3), // params[3] = srp_area
        cr: bh::ParameterSource::ParameterIndex(4),   // params[4] = Cr
        eclipse_model: bh::EclipseModel::Conical,
    };

    // Custom parameter layout example
    println!("\nCustom parameter layout example:");
    println!("  You can map parameters to any indices:");
    let _custom_drag = bh::DragConfiguration {
        model: bh::AtmosphericModel::HarrisPriester,
        area: bh::ParameterSource::ParameterIndex(5),  // Custom index
        cd: bh::ParameterSource::ParameterIndex(10),   // Custom index
    };
}

use brahe as bh;

fn main() {
    // Brahe provides several preset configurations for common scenarios

    // 1. two_body_gravity() - Point mass gravity only
    // Use for: Validation, comparison with Keplerian, quick estimates
    let _two_body = bh::ForceModelConfig::two_body_gravity();

    // 2. earth_gravity() - Spherical harmonic gravity only (20x20)
    // Use for: Studying gravity perturbations in isolation
    let _earth_gravity = bh::ForceModelConfig::earth_gravity();

    // 3. conservative_forces() - Gravity + third-body + relativity (no drag/SRP)
    // Use for: Long-term orbit evolution, conservative dynamics studies
    let _conservative = bh::ForceModelConfig::conservative_forces();

    // 4. default() - Balanced configuration for LEO to GEO
    // Use for: General mission analysis, initial studies
    let _default = bh::ForceModelConfig::default();

    // 5. leo_default() - Optimized for Low Earth Orbit
    // Use for: LEO missions where drag is dominant
    let _leo = bh::ForceModelConfig::leo_default();

    // 6. geo_default() - Optimized for Geostationary Orbit
    // Use for: GEO missions where SRP and third-body dominate
    let _geo = bh::ForceModelConfig::geo_default();

    // 7. high_fidelity() - Maximum precision
    // Use for: Precision orbit determination, research applications
    let _high_fidelity = bh::ForceModelConfig::high_fidelity();
}