Add mass driver station system with Lagrange point placement

- Lagrange point computation (L1-L5) for any Sun-planet pair in Rust
- Station generation: auto-place at Lagrange points by priority (inner → outer planets)
- Station panel UI: count slider (5-50), launch velocity slider (5-100 km/s) with info tooltip
- Blue diamond markers on 2D canvas with labels when zoomed in
- Active station list in sidebar (Earth L1, Mars L2, Jupiter L4, etc.)
- WASM API: generate_stations(), get_station_positions(), get_station_names()
- Station positions update every frame (co-rotating with planets at Lagrange points)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/orbital-mechanics/src/lagrange.rs

@@ -0,0 +1,105 @@
+use crate::bodies::CelestialBody;
+use crate::constants::*;
+use crate::orbits::position_at_epoch;
+use nalgebra::Vector3;
+
+/// Approximate position of a Lagrange point for a Sun-planet system.
+///
+/// L1: Between Sun and planet (closer to planet)
+/// L2: Beyond planet (away from Sun)
+/// L3: Opposite side of Sun from planet
+/// L4: 60° ahead of planet in its orbit
+/// L5: 60° behind of planet in its orbit
+///
+/// Returns position in AU, ecliptic coordinates.
+pub fn lagrange_point_position(
+    bodies: &[CelestialBody],
+    planet_id: usize,
+    point: u8, // 1-5
+    jd: f64,
+) -> Vector3<f64> {
+    let planet_pos = position_at_epoch(bodies, planet_id, jd);
+    let sun_pos = Vector3::zeros();
+
+    let r = planet_pos.norm(); // Distance from Sun
+    if r < 1e-10 {
+        return sun_pos;
+    }
+
+    let planet = &bodies[planet_id];
+    // Mass ratio: mu = m_planet / (m_sun + m_planet)
+    let mu = planet.mu / (MU_SUN + planet.mu);
+
+    // Hill sphere radius approximation
+    let r_hill = r * (mu / 3.0).powf(1.0 / 3.0);
+
+    // Unit vector from Sun to planet
+    let u = planet_pos / r;
+    // Perpendicular in ecliptic plane (rotate 90° CCW)
+    let u_perp = Vector3::new(-u.y, u.x, 0.0);
+
+    match point {
+        1 => {
+            // L1: between Sun and planet, distance r_hill inside planet orbit
+            planet_pos - u * r_hill
+        }
+        2 => {
+            // L2: beyond planet, distance r_hill outside planet orbit
+            planet_pos + u * r_hill
+        }
+        3 => {
+            // L3: opposite side of Sun, approximately at planet's orbital radius
+            -planet_pos * (1.0 + 5.0 * mu / 12.0)
+        }
+        4 => {
+            // L4: 60° ahead of planet (leading)
+            let angle = std::f64::consts::FRAC_PI_3; // 60°
+            let cos_a = angle.cos();
+            let sin_a = angle.sin();
+            (u * cos_a + u_perp * sin_a) * r
+        }
+        5 => {
+            // L5: 60° behind planet (trailing)
+            let angle = std::f64::consts::FRAC_PI_3;
+            let cos_a = angle.cos();
+            let sin_a = angle.sin();
+            (u * cos_a - u_perp * sin_a) * r
+        }
+        _ => sun_pos,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::bodies::all_bodies;
+
+    #[test]
+    fn test_l1_between_sun_and_planet() {
+        let bodies = all_bodies();
+        let earth_pos = position_at_epoch(&bodies, bodies::id::EARTH, J2000_JD);
+        let l1 = lagrange_point_position(&bodies, bodies::id::EARTH, 1, J2000_JD);
+
+        // L1 should be between Sun (0,0,0) and Earth
+        let l1_dist = l1.norm();
+        let earth_dist = earth_pos.norm();
+        assert!(l1_dist < earth_dist, "L1 should be closer to Sun than Earth");
+        assert!(l1_dist > 0.9, "L1 should be close to 1 AU");
+    }
+
+    #[test]
+    fn test_l4_l5_equilateral() {
+        let bodies = all_bodies();
+        let earth_pos = position_at_epoch(&bodies, bodies::id::EARTH, J2000_JD);
+        let l4 = lagrange_point_position(&bodies, bodies::id::EARTH, 4, J2000_JD);
+        let l5 = lagrange_point_position(&bodies, bodies::id::EARTH, 5, J2000_JD);
+
+        let earth_r = earth_pos.norm();
+        let l4_r = l4.norm();
+        let l5_r = l5.norm();
+
+        // L4 and L5 should be at roughly the same distance as the planet
+        assert!((l4_r - earth_r).abs() < 0.01);
+        assert!((l5_r - earth_r).abs() < 0.01);
+    }
+}

crates/orbital-mechanics/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod bodies;
 pub mod constants;
 pub mod kepler;
+pub mod lagrange;
 pub mod orbits;
 
 pub use nalgebra::Vector3;