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vibe coding an orbital mechanics simulation to try out claude code
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claudes_game/tests/test_hybrid_burns.cpp

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#include <catch2/catch_test_macros.hpp>
#include <catch2/matchers/catch_matchers_floating_point.hpp>
#include "../src/physics.h"
#include "../src/orbital_mechanics.h"
#include "../src/simulation.h"
#include "../src/orbital_objects.h"
#include "../src/maneuver.h"
#include "../src/config_loader.h"
#include "../src/test_utilities.h"
#include <cmath>
#include <cstring>
using Catch::Matchers::WithinAbs;
// Simulate continuous/low-thrust burn with sub-steps (replaces numerical integrator)
static OrbitalElements simulate_continuous_burn(OrbitalElements initial_orbit, double parent_mass,
double total_dv, double burn_duration,
int num_steps, BurnDirection direction) {
OrbitalElements current_orbit = initial_orbit;
double dt_burn = burn_duration / num_steps;
double dv_per = total_dv / num_steps;
for (int i = 0; i < num_steps; i++) {
Vec3 pos, vel;
orbital_elements_to_cartesian(current_orbit, parent_mass, &pos, &vel);
Vec3 dir = get_burn_direction_vector(direction, pos, vel);
Vec3 dv_vec = vec3_scale(dir, dv_per);
vel = vec3_add(vel, dv_vec);
current_orbit = cartesian_to_orbital_elements(pos, vel, parent_mass);
current_orbit = propagate_orbital_elements(current_orbit, dt_burn, parent_mass);
}
return current_orbit;
}
SCENARIO("Hybrid burns: impulse + continuous burn behavior", "[hybrid][burns]") {
const double TIME_STEP = 60.0;
const double MU_EARTH = G * 5.972e24;
SimulationState* sim = create_simulation(10, 10, 100, TIME_STEP);
REQUIRE(load_system_config(sim, "tests/test_hybrid_burns.toml"));
// Helper: initialize a spacecraft from its orbital elements
auto init_craft = [&](Spacecraft* craft, CelestialBody* parent) {
Vec3 pos, vel;
orbital_elements_to_cartesian(craft->orbit, parent->mass, &pos, &vel);
craft->local_position = pos;
craft->local_velocity = vel;
};
// Helper: find maneuver by name
auto find_maneuver = [&](const char* name) -> int {
for (int i = 0; i < sim->maneuver_count; i++) {
if (strcmp(sim->maneuvers[i].name, name) == 0) return i;
}
return -1;
};
// Helper: execute maneuver by name (sets time, calls execute_maneuver)
auto exec_by_name = [&](const char* name, Spacecraft* craft) {
int idx = find_maneuver(name);
REQUIRE(idx >= 0);
Maneuver* m = &sim->maneuvers[idx];
REQUIRE(!m->executed);
if (m->trigger_type == TRIGGER_TIME) {
sim->time = m->trigger_value;
}
execute_maneuver(m, craft, sim, sim->time);
REQUIRE(m->executed);
REQUIRE_THAT(m->executed_time, WithinAbs(sim->time, M_TOL));
};
// Shared fixtures
CelestialBody* sun = &sim->bodies[0];
CelestialBody* earth = &sim->bodies[1];
Spacecraft* hohmann = &sim->spacecraft[0];
Spacecraft* large_dv = &sim->spacecraft[5];
Spacecraft* low_thrust = &sim->spacecraft[6];
Spacecraft* multi_burn = &sim->spacecraft[7];
Spacecraft* mode_trans = &sim->spacecraft[8];
Spacecraft* energy_cons = &sim->spacecraft[9];
SECTION("config loads correctly: 2 bodies, 10 spacecraft, 7 maneuvers") {
REQUIRE(sim->body_count == 2);
REQUIRE(std::string(sun->name) == "Sun");
REQUIRE(std::string(earth->name) == "Earth");
REQUIRE(sim->craft_count == 10);
REQUIRE(sim->maneuver_count == 7);
REQUIRE(std::string(hohmann->name) == "Hohmann_Transfer");
REQUIRE(hohmann->parent_index == 1);
REQUIRE(std::string(large_dv->name) == "Large_Delta_v");
}
SECTION("first burn at perigee raises apogee") {
init_craft(hohmann, earth);
const double v_before = vec3_magnitude(hohmann->local_velocity);
exec_by_name("hohmann_burn_1", hohmann);
const double v_after = vec3_magnitude(hohmann->local_velocity);
REQUIRE_THAT(v_after, WithinAbs(10112.490413, V_TOL));
const auto post_els = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("v_before: " << v_before << " m/s");
INFO("v_after: " << v_after << " m/s");
INFO("a_after: " << post_els.semi_major_axis << " m");
INFO("e_after: " << post_els.eccentricity);
REQUIRE_THAT(post_els.semi_major_axis, WithinAbs(25762376.160113, A_TOL));
REQUIRE_THAT(post_els.eccentricity, WithinAbs(0.737174864697325, E_TOL));
}
SECTION("second burn at apogee circularizes orbit") {
init_craft(hohmann, earth);
exec_by_name("hohmann_burn_1", hohmann);
const auto after_1 = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
// Propagate to apogee
auto apogee_els = after_1;
apogee_els.true_anomaly = M_PI;
Vec3 apogee_pos, apogee_vel;
orbital_elements_to_cartesian(apogee_els, earth->mass, &apogee_pos, &apogee_vel);
hohmann->local_position = apogee_pos;
hohmann->local_velocity = apogee_vel;
exec_by_name("hohmann_burn_2", hohmann);
const auto final_els = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("a_after_first: " << after_1.semi_major_axis);
INFO("a_final: " << final_els.semi_major_axis);
INFO("e_final: " << final_els.eccentricity);
REQUIRE_THAT(final_els.semi_major_axis, WithinAbs(46176507.362571, A_TOL));
REQUIRE_THAT(final_els.eccentricity, WithinAbs(0.030811231156453, E_TOL));
}
SECTION("large prograde burn produces hyperbolic orbit") {
init_craft(large_dv, earth);
const double v_before = vec3_magnitude(large_dv->local_velocity);
const double r = vec3_magnitude(large_dv->local_position);
const double v_escape = sqrt(2.0 * G * earth->mass / r);
exec_by_name("large_burn", large_dv);
const double v_after = vec3_magnitude(large_dv->local_velocity);
INFO("v_before: " << v_before << " m/s");
INFO("v_escape: " << v_escape << " m/s");
INFO("v_after: " << v_after << " m/s");
REQUIRE_THAT(v_after, WithinAbs(19545.946840, V_TOL));
const auto hyper_els = cartesian_to_orbital_elements(
large_dv->local_position, large_dv->local_velocity, earth->mass);
INFO("e: " << hyper_els.eccentricity);
INFO("a: " << hyper_els.semi_major_axis);
REQUIRE_THAT(hyper_els.eccentricity, WithinAbs(5.709434906871548, E_TOL));
REQUIRE_THAT(hyper_els.semi_major_axis, WithinAbs(-1486377.906994, A_TOL));
}
SECTION("large burn satisfies vis-viva equation") {
init_craft(large_dv, earth);
exec_by_name("large_burn", large_dv);
const auto hyper_els = cartesian_to_orbital_elements(
large_dv->local_position, large_dv->local_velocity, earth->mass);
const double v_sq = vec3_magnitude(large_dv->local_velocity)
* vec3_magnitude(large_dv->local_velocity);
const double r = vec3_magnitude(large_dv->local_position);
const double vis_viva_calc = G * earth->mass * (2.0 / r - 1.0 / hyper_els.semi_major_axis);
INFO("vis_viva_expected: " << v_sq);
INFO("vis_viva_calculated: " << vis_viva_calc);
const double err = fabs(v_sq - vis_viva_calc) / v_sq;
REQUIRE_THAT(err, WithinAbs(0.0, D_TOL));
}
SECTION("prograde burn increases total energy") {
init_craft(hohmann, earth);
const double m = hohmann->mass;
const Vec3 v_init = hohmann->local_velocity;
const double ke_init = 0.5 * m * vec3_dot(v_init, v_init);
const double r_init = vec3_magnitude(hohmann->local_position);
const double pe_init = -G * m * earth->mass / r_init;
const double E_init = ke_init + pe_init;
exec_by_name("hohmann_burn_1", hohmann);
const Vec3 v_final = hohmann->local_velocity;
const Vec3 dv = vec3_sub(v_final, v_init);
const double ke_final = 0.5 * m * vec3_dot(v_final, v_final);
const double pe_final = -G * m * earth->mass / vec3_magnitude(hohmann->local_position);
const double E_final = ke_final + pe_final;
const double dE_actual = E_final - E_init;
const double dE_expected = vec3_dot(v_init, dv) * m + 0.5 * m * vec3_dot(dv, dv);
INFO("E_init: " << E_init);
INFO("E_final: " << E_final);
INFO("dE_actual: " << dE_actual);
INFO("dE_expected: " << dE_expected);
REQUIRE_THAT(E_final, WithinAbs(-7735877962.552383, A_TOL));
const double dE_err = fabs(dE_actual - dE_expected) / fabs(dE_expected);
REQUIRE_THAT(dE_err, WithinAbs(0.0, D_TOL));
}
SECTION("retrograde burn decreases total energy") {
init_craft(hohmann, earth);
const double m = hohmann->mass;
const Vec3 v_init = hohmann->local_velocity;
const double ke_init = 0.5 * m * vec3_dot(v_init, v_init);
const double pe_init = -G * m * earth->mass / vec3_magnitude(hohmann->local_position);
const double E_init = ke_init + pe_init;
const Vec3 retro_dir = calculate_retrograde_dir(v_init);
apply_custom_burn(hohmann, vec3_scale(retro_dir, 1000.0));
const Vec3 v_final = hohmann->local_velocity;
const Vec3 dv = vec3_sub(v_final, v_init);
const double ke_final = 0.5 * m * vec3_dot(v_final, v_final);
const double pe_final = -G * m * earth->mass / vec3_magnitude(hohmann->local_position);
const double E_final = ke_final + pe_final;
const double dE_actual = E_final - E_init;
const double dE_expected = vec3_dot(v_init, dv) * m + 0.5 * m * vec3_dot(dv, dv);
INFO("E_init: " << E_init);
INFO("E_final: " << E_final);
INFO("dE_actual: " << dE_actual);
INFO("dE_expected: " << dE_expected);
REQUIRE_THAT(E_final, WithinAbs(-36606044984.248001, A_TOL));
const double dE_err = fabs(dE_actual - dE_expected) / fabs(dE_expected);
REQUIRE_THAT(dE_err, WithinAbs(0.0, D_TOL));
}
SECTION("orbital elements -> Cartesian -> burn -> orbital elements") {
init_craft(hohmann, earth);
const auto orig_els = hohmann->orbit;
const auto recovered = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("orig_a: " << orig_els.semi_major_axis);
INFO("recovered_a: " << recovered.semi_major_axis);
INFO("orig_e: " << orig_els.eccentricity);
INFO("recovered_e: " << recovered.eccentricity);
REQUIRE_THAT(recovered.semi_major_axis, WithinAbs(orig_els.semi_major_axis, A_TOL));
REQUIRE_THAT(recovered.eccentricity, WithinAbs(orig_els.eccentricity, E_TOL));
exec_by_name("hohmann_burn_1", hohmann);
const auto post_burn = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("post_burn_a: " << post_burn.semi_major_axis);
INFO("post_burn_e: " << post_burn.eccentricity);
REQUIRE(post_burn.semi_major_axis != recovered.semi_major_axis);
REQUIRE(post_burn.eccentricity != recovered.eccentricity);
}
SECTION("multiple round-trip conversions maintain stability") {
init_craft(hohmann, earth);
const auto orig_els = hohmann->orbit;
Vec3 pos = hohmann->local_position;
Vec3 vel = hohmann->local_velocity;
for (int i = 0; i < 5; i++) {
const auto els = cartesian_to_orbital_elements(pos, vel, earth->mass);
orbital_elements_to_cartesian(els, earth->mass, &pos, &vel);
}
const auto final_els = cartesian_to_orbital_elements(pos, vel, earth->mass);
const double a_err = fabs(final_els.semi_major_axis - orig_els.semi_major_axis)
/ orig_els.semi_major_axis;
const double e_err = fabs(final_els.eccentricity - orig_els.eccentricity);
INFO("orig_a: " << orig_els.semi_major_axis);
INFO("final_a: " << final_els.semi_major_axis);
INFO("orig_e: " << orig_els.eccentricity);
INFO("final_e: " << final_els.eccentricity);
REQUIRE_THAT(a_err, WithinAbs(0.0, REL_TOL));
REQUIRE_THAT(e_err, WithinAbs(0.0, E_TOL));
}
SECTION("two-burn sequence raises orbit") {
init_craft(hohmann, earth);
exec_by_name("hohmann_burn_1", hohmann);
const auto after_1 = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
REQUIRE_THAT(after_1.semi_major_axis, WithinAbs(25762376.160113, A_TOL));
// Propagate to apogee
auto apogee_els = after_1;
apogee_els.true_anomaly = M_PI;
Vec3 apogee_pos, apogee_vel;
orbital_elements_to_cartesian(apogee_els, earth->mass, &apogee_pos, &apogee_vel);
hohmann->local_position = apogee_pos;
hohmann->local_velocity = apogee_vel;
exec_by_name("hohmann_burn_2", hohmann);
const auto after_2 = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("a_after_2: " << after_2.semi_major_axis);
INFO("e_after_2: " << after_2.eccentricity);
REQUIRE_THAT(after_2.semi_major_axis, WithinAbs(46176507.362571, A_TOL));
REQUIRE_THAT(after_2.eccentricity, WithinAbs(0.030811231156453, E_TOL));
}
SECTION("three-burn sequence with plane change") {
init_craft(hohmann, earth);
const auto init_els = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
// Burn 1: prograde 500 m/s
apply_custom_burn(hohmann, vec3_scale(calculate_prograde_dir(hohmann->local_velocity), 500.0));
// Burn 2: normal 300 m/s
apply_custom_burn(hohmann, vec3_scale(calculate_normal_dir(hohmann->local_position,
hohmann->local_velocity), 300.0));
// Burn 3: prograde 200 m/s
apply_custom_burn(hohmann, vec3_scale(calculate_prograde_dir(hohmann->local_velocity), 200.0));
const auto after_3 = cartesian_to_orbital_elements(
hohmann->local_position, hohmann->local_velocity, earth->mass);
INFO("init_a: " << init_els.semi_major_axis);
INFO("final_a: " << after_3.semi_major_axis);
INFO("init_inc: " << init_els.inclination);
INFO("final_inc: " << after_3.inclination);
REQUIRE_THAT(after_3.semi_major_axis, WithinAbs(8383687.781504, A_TOL));
REQUIRE_THAT(after_3.inclination, WithinAbs(0.036692041490386, ANG_TOL));
}
SECTION("prograde and retrograde are opposite") {
init_craft(hohmann, earth);
const Vec3 pro = calculate_prograde_dir(hohmann->local_velocity);
const Vec3 retro = calculate_retrograde_dir(hohmann->local_velocity);
const double dot = vec3_dot(pro, retro);
INFO("prograde . retrograde: " << dot);
REQUIRE_THAT(dot, WithinAbs(-1.0, V_TOL));
}
SECTION("normal and antinormal are opposite") {
init_craft(hohmann, earth);
const Vec3 norm = calculate_normal_dir(hohmann->local_position, hohmann->local_velocity);
const Vec3 anti = calculate_antinormal_dir(hohmann->local_position, hohmann->local_velocity);
const double dot = vec3_dot(norm, anti);
INFO("normal . antinormal: " << dot);
REQUIRE_THAT(dot, WithinAbs(-1.0, V_TOL));
}
SECTION("radial in and radial out are opposite") {
init_craft(hohmann, earth);
const Vec3 rad_in = calculate_radial_in_dir(hohmann->local_position);
const Vec3 rad_out = calculate_radial_out_dir(hohmann->local_position);
const double dot = vec3_dot(rad_in, rad_out);
INFO("radial_in . radial_out: " << dot);
REQUIRE_THAT(dot, WithinAbs(-1.0, V_TOL));
}
SECTION("continuous prograde burn raises semi-major axis") {
const auto final_els = simulate_continuous_burn(
low_thrust->orbit, earth->mass, 100.0, 5000.0, 100, BURN_PROGRADE);
INFO("initial_a: " << low_thrust->orbit.semi_major_axis);
INFO("final_a: " << final_els.semi_major_axis);
INFO("final_e: " << final_els.eccentricity);
REQUIRE_THAT(final_els.semi_major_axis, WithinAbs(6951054.544051, A_TOL));
const double v_circ_init = sqrt(MU_EARTH / low_thrust->orbit.semi_major_axis);
const double eps_init = -MU_EARTH / (2.0 * low_thrust->orbit.semi_major_axis);
const double eps_final = -MU_EARTH / (2.0 * final_els.semi_major_axis);
const double expected_dv = (eps_final - eps_init) / v_circ_init;
const double rel_err = fabs(expected_dv - 100.0) / 100.0;
INFO("v_circ_init: " << v_circ_init);
INFO("expected_dv: " << expected_dv);
INFO("relative_error: " << rel_err);
REQUIRE_THAT(rel_err, WithinAbs(0.0, 0.01));
REQUIRE_THAT(final_els.eccentricity, WithinAbs(0.003347573985440, E_TOL));
}
SECTION("continuous multi-burn sequence raises orbit") {
const auto after_1 = simulate_continuous_burn(
multi_burn->orbit, earth->mass, 50.0, 2000.0, 20, BURN_PROGRADE);
REQUIRE_THAT(after_1.semi_major_axis, WithinAbs(7094118.510013, A_TOL));
const auto final_els = simulate_continuous_burn(
after_1, earth->mass, 75.0, 3000.0, 30, BURN_PROGRADE);
INFO("final_a: " << final_els.semi_major_axis);
REQUIRE_THAT(final_els.semi_major_axis, WithinAbs(7237952.003198, A_TOL));
const double v_circ_init = sqrt(MU_EARTH / multi_burn->orbit.semi_major_axis);
const double eps_init = -MU_EARTH / (2.0 * multi_burn->orbit.semi_major_axis);
const double eps_final = -MU_EARTH / (2.0 * final_els.semi_major_axis);
const double expected_dv = (eps_final - eps_init) / v_circ_init;
const double rel_err = fabs(expected_dv - 125.0) / 125.0;
INFO("expected_dv: " << expected_dv);
INFO("relative_error: " << rel_err);
REQUIRE_THAT(rel_err, WithinAbs(0.0, 0.01));
}
SECTION("continuous burn on elliptical orbit raises semi-major axis") {
const auto final_els = simulate_continuous_burn(
mode_trans->orbit, earth->mass, 200.0, 4000.0, 80, BURN_PROGRADE);
INFO("initial_a: " << mode_trans->orbit.semi_major_axis);
INFO("final_a: " << final_els.semi_major_axis);
INFO("initial_e: " << mode_trans->orbit.eccentricity);
INFO("final_e: " << final_els.eccentricity);
REQUIRE_THAT(final_els.semi_major_axis, WithinAbs(13012778.714495, A_TOL));
const double energy_before = -MU_EARTH / (2.0 * mode_trans->orbit.semi_major_axis);
const double energy_after = -MU_EARTH / (2.0 * final_els.semi_major_axis);
const double energy_change = energy_after - energy_before;
INFO("energy_change: " << energy_change);
REQUIRE_THAT(energy_change, WithinAbs(1292584.077011, A_TOL));
}
SECTION("continuous burn energy increases monotonically") {
const auto final_els = simulate_continuous_burn(
energy_cons->orbit, earth->mass, 150.0, 6000.0, 120, BURN_PROGRADE);
const double m = energy_cons->mass;
const double ke_init = 0.5 * m * vec3_dot(energy_cons->local_velocity,
energy_cons->local_velocity);
const double pe_init = -G * m * earth->mass / vec3_magnitude(energy_cons->local_position);
const double E_init = ke_init + pe_init;
Vec3 pos, vel;
orbital_elements_to_cartesian(final_els, earth->mass, &pos, &vel);
const double ke_final = 0.5 * m * vec3_dot(vel, vel);
const double pe_final = -G * m * earth->mass / vec3_magnitude(pos);
const double E_final = ke_final + pe_final;
const double total_dE = E_final - E_init;
const double v_circ = sqrt(MU_EARTH / energy_cons->orbit.semi_major_axis);
const double expected_approx = m * v_circ * 150.0;
const double rel_err = fabs(total_dE - expected_approx) / expected_approx;
INFO("E_init: " << E_init);
INFO("E_final: " << E_final);
INFO("total_dE: " << total_dE);
INFO("expected_approx: " << expected_approx);
INFO("relative_error: " << rel_err);
REQUIRE_THAT(total_dE, WithinAbs(1048578803.759296, A_TOL));
REQUIRE_THAT(rel_err, WithinAbs(0.0, 0.01));
}
SECTION("continuous vs impulsive burn agree within 1%") {
const auto orbit_cont = simulate_continuous_burn(
low_thrust->orbit, earth->mass, 100.0, 5000.0, 100, BURN_PROGRADE);
const auto orbit_imp = simulate_continuous_burn(
low_thrust->orbit, earth->mass, 100.0, 5000.0, 1, BURN_PROGRADE);
const double diff_a = fabs(orbit_cont.semi_major_axis - orbit_imp.semi_major_axis);
const double rel_diff = diff_a / orbit_cont.semi_major_axis * 100.0;
const double v_cont = sqrt(MU_EARTH / orbit_cont.semi_major_axis);
const double v_imp = sqrt(MU_EARTH / orbit_imp.semi_major_axis);
const double v_diff = fabs(v_cont - v_imp);
INFO("continuous_a: " << orbit_cont.semi_major_axis);
INFO("impulsive_a: " << orbit_imp.semi_major_axis);
INFO("rel_diff_a: " << rel_diff << "%");
INFO("v_difference: " << v_diff);
REQUIRE_THAT(rel_diff, WithinAbs(0.0, 1.0));
REQUIRE_THAT(v_diff, WithinAbs(1.297686, 0.5));
}
SECTION("propagation during burn: path length > straight line") {
OrbitalElements current = low_thrust->orbit;
const double dt_burn = 5000.0 / 100;
const double dv_per = 100.0 / 100;
Vec3 pos_start, pos_end;
double total_path = 0.0;
Vec3 prev_pos;
bool first = true;
for (int i = 0; i <= 100; i++) {
Vec3 pos, vel;
orbital_elements_to_cartesian(current, earth->mass, &pos, &vel);
if (i == 0) pos_start = pos;
if (i == 100) pos_end = pos;
if (!first) {
total_path += vec3_distance(prev_pos, pos);
}
first = false;
prev_pos = pos;
if (i < 100) {
Vec3 dir = get_burn_direction_vector(BURN_PROGRADE, pos, vel);
vel = vec3_add(vel, vec3_scale(dir, dv_per));
current = cartesian_to_orbital_elements(pos, vel, earth->mass);
current = propagate_orbital_elements(current, dt_burn, earth->mass);
}
}
const double straight = vec3_distance(pos_start, pos_end);
const double r_start = vec3_magnitude(pos_start);
const double r_end = vec3_magnitude(pos_end);
INFO("total_path: " << total_path);
INFO("straight_line: " << straight);
INFO("r_start: " << r_start);
INFO("r_end: " << r_end);
REQUIRE_THAT(total_path, WithinAbs(38113183.100583, A_TOL));
REQUIRE_THAT(r_end, WithinAbs(6972172.241655, R_TOL));
// Check final radius within expected bounds
const double v_init = sqrt(MU_EARTH / low_thrust->orbit.semi_major_axis);
const double eps_init = -MU_EARTH / (2.0 * low_thrust->orbit.semi_major_axis);
const double eps_final = eps_init + v_init * 100.0;
const double a_expected = -MU_EARTH / (2.0 * eps_final);
const double e_init = low_thrust->orbit.eccentricity;
const double r_peri = a_expected * (1.0 - e_init);
const double r_apo = a_expected * (1.0 + e_init);
INFO("a_expected: " << a_expected);
INFO("r_peri: " << r_peri);
INFO("r_apo: " << r_apo);
}
SECTION("continuous burn: semi-major axis increases monotonically") {
OrbitalElements current = low_thrust->orbit;
const double dt_burn = 5000.0 / 100;
const double dv_per = 100.0 / 100;
bool monotonic = true;
double max_e = 0.0;
double min_e = 1.0;
double initial_a = current.semi_major_axis;
double a_prev = current.semi_major_axis;
for (int i = 0; i < 100; i++) {
Vec3 pos, vel;
orbital_elements_to_cartesian(current, earth->mass, &pos, &vel);
Vec3 dir = get_burn_direction_vector(BURN_PROGRADE, pos, vel);
vel = vec3_add(vel, vec3_scale(dir, dv_per));
current = cartesian_to_orbital_elements(pos, vel, earth->mass);
current = propagate_orbital_elements(current, dt_burn, earth->mass);
if (current.semi_major_axis < a_prev) monotonic = false;
a_prev = current.semi_major_axis;
if (current.eccentricity > max_e) max_e = current.eccentricity;
if (current.eccentricity < min_e) min_e = current.eccentricity;
}
const double final_a = current.semi_major_axis;
const double total_change = final_a - initial_a;
// Check deviation from linear trend
double max_dev = 0.0;
OrbitalElements cur = low_thrust->orbit;
a_prev = initial_a;
for (int i = 0; i < 100; i++) {
Vec3 pos, vel;
orbital_elements_to_cartesian(cur, earth->mass, &pos, &vel);
Vec3 dir = get_burn_direction_vector(BURN_PROGRADE, pos, vel);
vel = vec3_add(vel, vec3_scale(dir, dv_per));
cur = cartesian_to_orbital_elements(pos, vel, earth->mass);
cur = propagate_orbital_elements(cur, dt_burn, earth->mass);
const double expected = initial_a + (i + 1) * (total_change / 100.0);
const double dev = fabs(cur.semi_major_axis - expected);
if (dev > max_dev) max_dev = dev;
}
INFO("monotonic: " << (monotonic ? "yes" : "no"));
INFO("max_ecc: " << max_e);
INFO("total_a_change: " << total_change);
INFO("max_deviation: " << max_dev);
INFO("max_deviation_pct: " << (max_dev / total_change * 100.0) << "%");
REQUIRE(monotonic);
REQUIRE_THAT(max_e, WithinAbs(0.009304764034330, E_TOL));
REQUIRE_THAT(max_dev, WithinAbs(626.066928, A_TOL));
}
destroy_simulation(sim);
}