spacecraft orientation determination (#21)

* spacecraft orientation determination

* add dramatic attitude changes test data

* add example and update readme

README.md

@@ -23,6 +23,7 @@
     - [x] Impulse Maneuvers
     - [x] Phase Maneuvers
     - [x] Plane Change Maneuvers
+- [x] Orientation Determination
 
 #### Astronomical
 
@@ -80,6 +81,8 @@ exe.root_module.addImport("astroz", astroz_mod);
 
 - #### [Orbit Phase Change](examples/orbit_phase_change.zig)
 
+- #### [Orbit Orientation Determination](examples/simple_spacecraft_orientation.zig)
+
 - #### [Parse Vita49](examples/parse_vita49.zig)
 
 - #### [Parse Vita49 with Callback](examples/parse_vita49_callback.zig)

examples/simple_spacecraft_orientation.zig

@@ -0,0 +1,65 @@
+const std = @import("std");
+const astroz = @import("astroz");
+const constants = astroz.constants;
+const TLE = astroz.tle.TLE;
+const spacecraft = astroz.spacecraft;
+const Spacecraft = spacecraft.Spacecraft;
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+    const allocator = gpa.allocator();
+
+    const raw_tle =
+        \\1 55909U 23035B   24187.51050877  .00023579  00000+0  16099-2 0  9998
+        \\2 55909  43.9978 311.8012 0011446 278.6226  81.3336 15.05761711 71371
+    ;
+    var test_tle = try TLE.parse(raw_tle, allocator);
+    defer test_tle.deinit();
+    var sc = Spacecraft.init("dummy_sc", test_tle, 300.000, spacecraft.SatelliteSize.Cube, constants.earth, allocator);
+    defer sc.deinit();
+
+    sc.angular_velocity = .{ 0.0, 0.0, 0.0 };
+
+    const dt = 120.0; // 2 mins time step
+    const simulation_time = 3 * 24 * 60 * 60.0; // 3 days in seconds
+    const orbital_period = 90 * 60.0; // 90 minutes orbital period
+    var t: f64 = 0;
+
+    while (t < simulation_time) : (t += dt) {
+        // Simulate a dramatic torque effect
+        const torque_x = 0.001 * @sin(2 * std.math.pi * t / (orbital_period * 2));
+        const torque_y = 0.0005 * @cos(2 * std.math.pi * t / (orbital_period * 3));
+        const torque_z = 0.0002 * @sin(2 * std.math.pi * t / orbital_period);
+
+        // Update angular velocity based on torque (simplified)
+        sc.angular_velocity[0] += torque_x * dt;
+        sc.angular_velocity[1] += torque_y * dt;
+        sc.angular_velocity[2] += torque_z * dt;
+
+        // Update attitude
+        sc.updateAttitude();
+        sc.propagateAttitude(dt);
+
+        // Simulate simple circular orbit
+        const orbit_radius = 7000.0;
+        const x = orbit_radius * @cos(2 * std.math.pi * t / orbital_period);
+        const y = orbit_radius * @sin(2 * std.math.pi * t / orbital_period);
+        const z = 0.0;
+
+        std.log.debug("Showing orbiting info: {d},{d},{d},{d},{d},{d},{d},{d},{d},{d},{d}\n", .{
+            t,
+            sc.quaternion[0],
+            sc.quaternion[1],
+            sc.quaternion[2],
+            sc.quaternion[3],
+            sc.angular_velocity[0],
+            sc.angular_velocity[1],
+            sc.angular_velocity[2],
+            x,
+            y,
+            z,
+        });
+    }
+}
+