GravityGradientModel.h

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/*
Gravity gradient torque model header file
 
Author: Sam Matez
*/
 
#ifndef MODELS_ENVIRONMENT_GRAVITY_GRADIENT_MODEL_H
#define MODELS_ENVIRONMENT_GRAVITY_GRADIENT_MODEL_H
 
#include "six_dof_dynamics/Body.hpp"
#include "core/macros.h"
#include "architecture/Tasks.h"
#include "utils/frameutils.hpp"
#include "simulation/Model.h"
#include "utils/planetdefaults.h"
 
namespace modelspace {
 
    /**
     * @brief   Gravity Gradient Model
     * 
     * This model calculates the gravity gradient torque force 
     * resulting from differences in axial inertia on a spacecraft.
     * The equations used for this calculation come from "Analytical
     * Mechanics of Space Systems (Fourth Edition), by Hanspeter
     * Schaub and John L. Junkins", page 226 (eq. 4.158). The gravity
     * gradient torque calculation is done in the body frame (Body
     * frame position and inertia).
     * 
     * Author: Sam Matez
     * Email: sam.matez@attx.tech
     * 
    */
    class GravityGradientModel : public Model {
    public:
        // Model params
        //         NAME                     TYPE                    DEFAULT VALUE
        START_PARAMS
            /** This is the gravitational parameter of our parent planet. Defaults to
             * Earth's gravitational parameter for ease of use */
            SIGNAL(mu,                      double,                 clockwerk::earth_wgs84.mu)
        END_PARAMS
 
        // Model inputs
        //         NAME                     TYPE                    DEFAULT VALUE
        START_INPUTS
            /** The position of the body with respect to PCI frame, expressed in PCI coordinates */
            SIGNAL(pos_body_pci,            CartesianVector3D,      CartesianVector3D({0.0, 0.0, 0.0}))
            /** The attitude of the body with respect ot the PCI frame, in quaternions */
            SIGNAL(quat_body_pci,           QuaternionD,            QuaternionD({1.0, 0.0, 0.0, 0.0}))
            /** The inertia tensor expressed in the body frame */
            SIGNAL(inertiatensor_body_body,       Matrix3D,      Matrix3D({{1.0, 0.0, 0.0}, {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0}}))
        END_INPUTS
 
        // Model outputs
        //         NAME                     TYPE                    DEFAULT VALUE
        START_OUTPUTS
            /** The tourque vector acting on the body due to gravity gradient effects wrt to the body frame */
            SIGNAL(ggTorque_body_body,      CartesianVector3D,      CartesianVector3D({0.0, 0.0, 0.0}))
        END_OUTPUTS
 
        // Model-specific implementations of startup and derivative
        GravityGradientModel();
        GravityGradientModel(Model &pnt, const std::string &m_name="gravity_gradient_torque");
        GravityGradientModel(SimulationExecutive &e, const std::string &m_name="gravity_gradient_torque");
        GravityGradientModel(Model &pnt, int schedule_slot, const std::string &m_name="gravity_gradient_torque");
        GravityGradientModel(SimulationExecutive &e, int schedule_slot, const std::string &m_name="gravity_gradient_torque");
        ~GravityGradientModel() {}
 
    protected:
        // Execute in protected
        int execute();
 
        // Temporary vectors and variables to carry out our calculations
        CartesianVector3D _pos_body_pci__body;
        double _r;
        double _multiplier;
        CartesianVector3D _ggTorque;
 
    };
 
}
 
#endif