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214 lines
6.7 KiB
C++
214 lines
6.7 KiB
C++
#include "Integrator.hh"
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#include <math.h>
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#include <iostream>
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// This is from matrix_macros.h in Trick.
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/* matrix times vector : prod[i] = mat[i][j] * vect[i] */
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#define MxV( prod , mat , vect ) { \
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prod[0] = mat[0][0] * vect[0] + mat[0][1] * vect[1] + mat[0][2] * vect[2] ; \
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prod[1] = mat[1][0] * vect[0] + mat[1][1] * vect[1] + mat[1][2] * vect[2] ; \
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prod[2] = mat[2][0] * vect[0] + mat[2][1] * vect[1] + mat[2][2] * vect[2] ; \
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}
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// GRAVITATIONAL_CONSTANT (Nm2/kg2)
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#define GRAVITATIONAL_CONSTANT 6.67e-11
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// LUNAR_MASS (kg)
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#define LUNAR_MASS 7.36e22
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// LUNAR RADIUS (m)
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#define LUNAR_RADIUS 1737400.0
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#define RADIANS_PER_DEGREE 0.0174532925
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typedef struct {
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double mass;
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double pos[3];
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double vel[3];
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double acc[3];
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} SATELLITE;
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typedef struct {
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double radius;
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double mass;
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} PLANET;
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typedef struct {
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double semi_major_axis; /* (m) */
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double eccentricity; /* (--) */
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double inclination; /* (r) */
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double argument_of_perigee; /* (r) */
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double right_ascension; /* (r) */
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double true_anomaly; /* (r) */
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} ORBITAL_ELEMENTS;
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void calc_gravity( SATELLITE * S,
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PLANET * P,
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double * G ) {
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double distance;
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double pos_hat[3];
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double g_force_mag;
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// Calculate Gravitational Force
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distance = sqrt( S->pos[0] * S->pos[0] +
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S->pos[1] * S->pos[1] +
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S->pos[2] * S->pos[2] );
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pos_hat[0] = S->pos[0] / distance ;
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pos_hat[1] = S->pos[1] / distance ;
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pos_hat[2] = S->pos[2] / distance ;
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g_force_mag = ( GRAVITATIONAL_CONSTANT * P->mass * S->mass ) / ( distance * distance ) ;
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G[0] = g_force_mag * - pos_hat[0] ;
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G[1] = g_force_mag * - pos_hat[1] ;
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G[2] = g_force_mag * - pos_hat[2] ;
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}
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//
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// Reference: ISS SIGI Attitude Processor Orbit Equations EG2/Rodolfo Gonzalez 20 Aug 2003
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void orb_elem_to_intl( ORBITAL_ELEMENTS * O, /* IN */
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PLANET * P, /* IN */
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double * R_intl, /* OUT */
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double * V_intl ) { /* OUT */
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double ra, wp, in ;
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double M_pci_perif[3][3]; /* Perifocal --> Inertial transform */
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double semi_latus_rectum;
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double r_magnitude;
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double r_perifocal[3];
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double v_perifocal[3];
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double v_mag;
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semi_latus_rectum = O->semi_major_axis * ( 1.0 - O->eccentricity * O->eccentricity );
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r_magnitude = semi_latus_rectum / (1.0 + O->eccentricity * cos( O->true_anomaly ));
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r_perifocal[0] = r_magnitude * cos( O->true_anomaly);
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r_perifocal[1] = r_magnitude * sin( O->true_anomaly);
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r_perifocal[2] = 0;
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v_mag = sqrt( GRAVITATIONAL_CONSTANT * P->mass / semi_latus_rectum);
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v_perifocal[0] = v_mag * (-sin(O->true_anomaly));
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v_perifocal[1] = v_mag * (O->eccentricity + cos(O->true_anomaly));
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v_perifocal[2] = 0;
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ra = O->right_ascension;
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wp = O->argument_of_perigee;
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in = O->inclination;
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M_pci_perif[0][0] = cos(ra)*cos(wp) - sin(ra)*cos(in)*sin(wp) ;
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M_pci_perif[0][1] = -cos(ra)*sin(wp) - sin(ra)*cos(in)*cos(wp) ;
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M_pci_perif[0][2] = sin(ra)*sin(in);
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M_pci_perif[1][0] = sin(ra)*cos(wp) + cos(ra)*cos(in)*sin(wp) ;
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M_pci_perif[1][1] = -sin(ra)*sin(wp) + cos(ra)*cos(in)*cos(wp) ;
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M_pci_perif[1][2] = -cos(ra)*sin(in) ;
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M_pci_perif[2][0] = sin(in)*sin(wp) ;
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M_pci_perif[2][1] = sin(in)*cos(wp) ;
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M_pci_perif[2][2] = cos(in) ;
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MxV( R_intl , M_pci_perif , r_perifocal) ;
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MxV( V_intl , M_pci_perif , v_perifocal) ;
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}
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void deriv(SATELLITE *S, PLANET *P) {
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double gforce[3];
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calc_gravity(S, P, gforce );
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S->acc[0] = gforce[0] / S->mass ;
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S->acc[1] = gforce[1] / S->mass ;
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S->acc[2] = gforce[2] / S->mass ;
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}
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int main(int argc, const char* argv[]) {
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SATELLITE satellite;
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PLANET planet;
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ORBITAL_ELEMENTS orbital_elements;
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long tick = 0;
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double seconds_per_tick = 1.0;
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double sim_time = 0.0;
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// Initialization
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satellite.mass = 100;
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planet.mass = LUNAR_MASS;
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planet.radius = LUNAR_RADIUS;
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orbital_elements.semi_major_axis = 2000000; // meters
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orbital_elements.eccentricity = 0.2;
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orbital_elements.inclination = 5.0 * RADIANS_PER_DEGREE;
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orbital_elements.argument_of_perigee = 0.0;
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orbital_elements.right_ascension = 0.0; // radians
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orbital_elements.true_anomaly = 0.0; // radians
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orb_elem_to_intl( &orbital_elements,
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&planet,
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satellite.pos,
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satellite.vel);
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Trick::Integrator *I = getIntegrator( Euler, 6, 1.0);
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do { // sim loop
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sim_time = tick * seconds_per_tick ;
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std::cout << "sim_time = " << sim_time << std::endl;
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do { // Integration Loop
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I->time = sim_time;
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std::cout << "step #" << I->intermediate_step << std::endl; std::cout.flush();
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std::cout << "deriv ..."; std::cout.flush();
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deriv( &satellite, &planet);
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std::cout << "done." << std::endl; std::cout.flush();
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std::cout << "loading state ..."; std::cout.flush();
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I->state[0] = satellite.pos[0];
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I->state[1] = satellite.pos[1];
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I->state[2] = satellite.pos[2];
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I->state[3] = satellite.vel[0];
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I->state[4] = satellite.vel[1];
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I->state[5] = satellite.vel[2];
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std::cout << "done." << std::endl; std::cout.flush();
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std::cout << "loading state deriv ..."; std::cout.flush();
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I->deriv[I->intermediate_step][0] = satellite.vel[0];
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I->deriv[I->intermediate_step][1] = satellite.vel[1];
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I->deriv[I->intermediate_step][2] = satellite.vel[2];
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I->deriv[I->intermediate_step][3] = satellite.acc[0];
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I->deriv[I->intermediate_step][4] = satellite.acc[1];
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I->deriv[I->intermediate_step][5] = satellite.acc[2];
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std::cout << "done." << std::endl; std::cout.flush();
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std::cout << "integrate" << std::endl; std::cout.flush();
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I->integrate();
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std::cout << "done." << std::endl; std::cout.flush();
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satellite.pos[0] = I->state_ws[I->intermediate_step][0];
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satellite.pos[1] = I->state_ws[I->intermediate_step][1];
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satellite.pos[2] = I->state_ws[I->intermediate_step][2];
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satellite.vel[0] = I->state_ws[I->intermediate_step][3];
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satellite.vel[1] = I->state_ws[I->intermediate_step][4];
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satellite.vel[2] = I->state_ws[I->intermediate_step][5];
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} while ( I->intermediate_step);
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std::cout << "(" << satellite.pos[0] <<","<< satellite.pos[1] <<","<< satellite.pos[2] << ")" << std::endl;
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tick++;
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} while (sim_time < 10.0);
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}
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