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/mass-driver-core/src/station.rs

@@ -1,3 +1,8 @@
+use orbital_mechanics::bodies;
+use orbital_mechanics::bodies::CelestialBody;
+use orbital_mechanics::lagrange;
+use orbital_mechanics::orbits;
+use nalgebra::Vector3;
 use serde::{Deserialize, Serialize};
 
 /// How a station is placed in the solar system.
@@ -12,29 +17,13 @@ pub enum StationPlacement {
         w: f64,       // Argument of perihelion (degrees)
         m0: f64,      // Mean anomaly at epoch (degrees)
     },
-    /// Station in orbit around a planet
-    PlanetaryOrbit {
-        parent_body_id: usize,
-        altitude_km: f64,
-        inclination: f64,
-    },
     /// Station at a Lagrange point
     LagrangePoint {
-        primary_body_id: usize,   // e.g., Sun
+        planet_id: usize,
-        secondary_body_id: usize, // e.g., Earth
+        point: u8, // 1-5
-        point: LagrangePointId,
     },
 }
 
-#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
-pub enum LagrangePointId {
-    L1,
-    L2,
-    L3,
-    L4,
-    L5,
-}
-
 /// A mass driver relay station.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Station {
@@ -42,3 +31,116 @@ pub struct Station {
     pub name: String,
     pub placement: StationPlacement,
 }
+
+/// Simulation configuration for mass driver network.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SimConfig {
+    pub stations: Vec<Station>,
+    pub launch_velocity_kms: f64, // km/s
+}
+
+/// Compute position of a station at a given Julian Date.
+pub fn station_position(
+    station: &Station,
+    all_bodies: &[CelestialBody],
+    jd: f64,
+) -> Vector3<f64> {
+    match &station.placement {
+        StationPlacement::SolarOrbit { a, e, i, omega, w, m0 } => {
+            // Treat station as a body with fixed elements
+            let body = CelestialBody {
+                name: "station",
+                id: 999,
+                mu: 0.0,
+                radius_km: 0.0,
+                elements: orbital_mechanics::bodies::KeplerianElements {
+                    a: *a,
+                    e: *e,
+                    i: *i,
+                    l: *m0 + *w + *omega, // mean longitude = M + w + Omega
+                    w_bar: *w + *omega,    // longitude of perihelion
+                    omega: *omega,
+                },
+                rates: orbital_mechanics::bodies::KeplerianRates {
+                    a: 0.0, e: 0.0, i: 0.0,
+                    // Mean longitude rate from Kepler's third law: n = sqrt(mu/a^3) in deg/century
+                    l: (orbital_mechanics::constants::MU_SUN
+                        / (*a * orbital_mechanics::constants::AU_KM).powi(3))
+                        .sqrt()
+                        * orbital_mechanics::constants::SECONDS_PER_DAY
+                        * orbital_mechanics::constants::DAYS_PER_CENTURY
+                        * (180.0 / std::f64::consts::PI),
+                    w_bar: 0.0,
+                    omega: 0.0,
+                },
+                color: [255, 255, 255],
+            };
+            // Use a temporary slice with just Sun + this station
+            let temp = vec![all_bodies[0].clone(), body];
+            orbits::position_at_epoch(&temp, 1, jd)
+        }
+        StationPlacement::LagrangePoint { planet_id, point } => {
+            lagrange::lagrange_point_position(all_bodies, *planet_id, *point, jd)
+        }
+    }
+}
+
+/// Compute positions of all stations. Returns flat [x,y,z, x,y,z, ...] in AU.
+pub fn all_station_positions(
+    stations: &[Station],
+    all_bodies: &[CelestialBody],
+    jd: f64,
+) -> Vec<f64> {
+    let mut result = Vec::with_capacity(stations.len() * 3);
+    for station in stations {
+        let pos = station_position(station, all_bodies, jd);
+        result.push(pos.x);
+        result.push(pos.y);
+        result.push(pos.z);
+    }
+    result
+}
+
+/// Generate a default set of stations for a given target count.
+/// Places stations at key Lagrange points of the major planets.
+pub fn generate_default_stations(target_count: usize) -> Vec<Station> {
+    let mut stations = Vec::new();
+    let mut id = 0;
+
+    // Priority order: inner planets first, then outer
+    let planet_priority = [
+        (bodies::id::EARTH, "Earth"),
+        (bodies::id::MARS, "Mars"),
+        (bodies::id::VENUS, "Venus"),
+        (bodies::id::JUPITER, "Jupiter"),
+        (bodies::id::MERCURY, "Mercury"),
+        (bodies::id::SATURN, "Saturn"),
+        (bodies::id::NEPTUNE, "Neptune"),
+        (bodies::id::URANUS, "Uranus"),
+        (bodies::id::PLUTO, "Pluto"),
+        (bodies::id::CERES, "Ceres"),
+    ];
+
+    // Lagrange points to place at each planet (in priority order)
+    let lp_priority: &[u8] = &[1, 2, 4, 5, 3];
+
+    for &lp in lp_priority {
+        for &(planet_id, planet_name) in &planet_priority {
+            if stations.len() >= target_count {
+                return stations;
+            }
+            stations.push(Station {
+                id,
+                name: format!("{} L{}", planet_name, lp),
+                placement: StationPlacement::LagrangePoint {
+                    planet_id,
+                    point: lp,
+                },
+            });
+            id += 1;
+        }
+    }
+
+    stations.truncate(target_count);
+    stations
+}

crates/mass-driver-wasm/src/api.rs

@@ -1,3 +1,4 @@
+use mass_driver_core::station;
 use orbital_mechanics::bodies;
 use orbital_mechanics::orbits;
 use wasm_bindgen::prelude::*;
@@ -66,3 +67,34 @@ pub fn get_orbit_points(body_id: usize, jd: f64, samples: usize) -> Vec<f64> {
     }
     orbits::orbit_points(&all, body_id, jd, samples)
 }
+
+/// Generate default stations and return their configuration as JSON.
+#[wasm_bindgen]
+pub fn generate_stations(count: usize) -> String {
+    let stations = station::generate_default_stations(count);
+    serde_json::to_string(&stations).unwrap()
+}
+
+/// Get station positions at a given Julian Date.
+/// Takes a JSON config string (from generate_stations) and returns
+/// Float64Array of [x0, y0, z0, x1, y1, z1, ...] in AU.
+#[wasm_bindgen]
+pub fn get_station_positions(stations_json: &str, jd: f64) -> Vec<f64> {
+    let stations: Vec<station::Station> = match serde_json::from_str(stations_json) {
+        Ok(s) => s,
+        Err(_) => return vec![],
+    };
+    let all_bodies = bodies::all_bodies();
+    station::all_station_positions(&stations, &all_bodies, jd)
+}
+
+/// Get station names from a config JSON string.
+#[wasm_bindgen]
+pub fn get_station_names(stations_json: &str) -> String {
+    let stations: Vec<station::Station> = match serde_json::from_str(stations_json) {
+        Ok(s) => s,
+        Err(_) => return "[]".to_string(),
+    };
+    let names: Vec<&str> = stations.iter().map(|s| s.name.as_str()).collect();
+    serde_json::to_string(&names).unwrap()
+}

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;

frontend/src/lib/render/canvas2d/SolarSystem2D.ts

@@ -17,6 +17,9 @@ export class SolarSystem2DRenderer {
 	private positions: Float64Array = new Float64Array(0);
 	private velocities: Float64Array = new Float64Array(0);
 	private orbitPoints: Map<number, Float64Array> = new Map();
+	private stationPositions: Float64Array = new Float64Array(0);
+	private stationNames: string[] = [];
+	private showStations: boolean = true;
 	private isDragging = false;
 	private lastMouse = { x: 0, y: 0 };
 	private animFrameId: number = 0;
@@ -77,6 +80,12 @@ export class SolarSystem2DRenderer {
 		this.orbitPoints.set(bodyId, points);
 	}
 
+	updateStations(positions: Float64Array, names: string[], visible: boolean) {
+		this.stationPositions = positions;
+		this.stationNames = names;
+		this.showStations = visible;
+	}
+
 	render() {
 		const { canvas, ctx } = this;
 		const dpr = window.devicePixelRatio || 1;
@@ -115,6 +124,15 @@ export class SolarSystem2DRenderer {
 			}
 		}
 
+		// Draw stations
+		if (this.showStations && this.stationPositions.length > 0) {
+			for (let i = 0; i < this.stationNames.length; i++) {
+				const x = this.stationPositions[i * 3];
+				const y = this.stationPositions[i * 3 + 1];
+				this.drawStation(x, y, this.stationNames[i]);
+			}
+		}
+
 		// Scale indicator
 		this.drawScaleBar(rect.width, rect.height);
 	}
@@ -269,6 +287,32 @@ export class SolarSystem2DRenderer {
 		ctx.fillText(info.name, sx + size + 4, sy + 3);
 	}
 
+	private drawStation(xAU: number, yAU: number, name: string) {
+		const ctx = this.ctx;
+		const [sx, sy] = this.auToScreen(xAU, yAU);
+
+		// Diamond shape
+		const s = 3;
+		ctx.fillStyle = 'rgba(74, 158, 255, 0.6)';
+		ctx.strokeStyle = 'rgba(74, 158, 255, 0.8)';
+		ctx.lineWidth = 1;
+		ctx.beginPath();
+		ctx.moveTo(sx, sy - s);
+		ctx.lineTo(sx + s, sy);
+		ctx.lineTo(sx, sy + s);
+		ctx.lineTo(sx - s, sy);
+		ctx.closePath();
+		ctx.fill();
+		ctx.stroke();
+
+		// Label (only show when zoomed in enough)
+		if (this.getScale() > 50) {
+			ctx.fillStyle = 'rgba(74, 158, 255, 0.5)';
+			ctx.font = '8px monospace';
+			ctx.fillText(name, sx + s + 3, sy + 3);
+		}
+	}
+
 	private drawScaleBar(w: number, h: number) {
 		const ctx = this.ctx;
 		const scale = this.getScale();

frontend/src/lib/stores/stations.svelte.ts

@@ -0,0 +1,10 @@
+class StationsState {
+	stationCount = $state(20);
+	launchVelocityKms = $state(30); // km/s — sci-fi default
+	stationsJson = $state('[]');
+	stationNames = $state<string[]>([]);
+	stationPositions = $state<Float64Array>(new Float64Array(0));
+	visible = $state(true);
+}
+
+export const stations = new StationsState();

frontend/src/lib/wasm/bridge.ts

@@ -39,3 +39,21 @@ export function getOrbitPoints(bodyId: number, jd: number, samples: number = 180
 	if (!wasm) return new Float64Array(0);
 	return wasm.get_orbit_points(bodyId, jd, samples);
 }
+
+export function generateStations(count: number): string {
+	const wasm = getWasm();
+	if (!wasm) return '[]';
+	return wasm.generate_stations(count);
+}
+
+export function getStationPositions(stationsJson: string, jd: number): Float64Array {
+	const wasm = getWasm();
+	if (!wasm) return new Float64Array(0);
+	return wasm.get_station_positions(stationsJson, jd);
+}
+
+export function getStationNames(stationsJson: string): string[] {
+	const wasm = getWasm();
+	if (!wasm) return [];
+	return JSON.parse(wasm.get_station_names(stationsJson));
+}

frontend/src/routes/(simulator)/components/Canvas2DView.svelte

@@ -2,7 +2,8 @@
 	import { onMount, onDestroy } from 'svelte';
 	import { SolarSystem2DRenderer } from '$lib/render/canvas2d/SolarSystem2D';
 	import { simulation } from '$lib/stores/simulation.svelte';
-	import { getBodyPositions, getBodyVelocities, getBodyInfos, getOrbitPoints } from '$lib/wasm/bridge';
+	import { stations } from '$lib/stores/stations.svelte';
+	import { getBodyPositions, getBodyVelocities, getBodyInfos, getOrbitPoints, getStationPositions } from '$lib/wasm/bridge';
 
 	let canvas: HTMLCanvasElement;
 	let renderer: SolarSystem2DRenderer;
@@ -41,7 +42,12 @@
 				const velocities = getBodyVelocities(simulation.currentJD);
 				renderer.updateBodies(simulation.bodyInfos, simulation.bodyPositions, velocities);
 
-				// Compute orbits on first frame and refresh every 600 frames (~10s)
+				// Update station positions
+				if (stations.stationsJson !== '[]') {
+					stations.stationPositions = getStationPositions(stations.stationsJson, simulation.currentJD);
+					renderer.updateStations(stations.stationPositions, stations.stationNames, stations.visible);
+				}
+
 				if (!orbitsComputed || frameCount % 600 === 0) {
 					computeOrbits();
 				}

frontend/src/routes/(simulator)/components/StationPanel.svelte

@@ -0,0 +1,99 @@
+<script lang="ts">
+	import { stations } from '$lib/stores/stations.svelte';
+	import { generateStations, getStationNames } from '$lib/wasm/bridge';
+	import { simulation } from '$lib/stores/simulation.svelte';
+
+	function updateStations() {
+		if (!simulation.wasmReady) return;
+		stations.stationsJson = generateStations(stations.stationCount);
+		stations.stationNames = getStationNames(stations.stationsJson);
+	}
+
+	// Initialize on first load
+	$effect(() => {
+		if (simulation.wasmReady) {
+			updateStations();
+		}
+	});
+
+	// Regenerate when count changes
+	$effect(() => {
+		const _ = stations.stationCount;
+		if (simulation.wasmReady) {
+			updateStations();
+		}
+	});
+</script>
+
+<div class="flex flex-col gap-3 p-3 bg-[var(--bg-panel)] rounded-lg border border-white/5">
+	<div class="flex items-center justify-between">
+		<h3 class="text-xs font-semibold uppercase tracking-wider text-[var(--text-secondary)]">
+			Relay Stations
+		</h3>
+		<label class="flex items-center gap-1.5 text-xs text-[var(--text-secondary)] cursor-pointer">
+			<input
+				type="checkbox"
+				bind:checked={stations.visible}
+				class="rounded border-white/20 bg-transparent"
+			/>
+			Show
+		</label>
+	</div>
+
+	<!-- Station count slider -->
+	<div>
+		<div class="flex justify-between text-xs mb-1">
+			<span class="text-[var(--text-secondary)]">Count</span>
+			<span class="text-[var(--text-primary)] font-mono">{stations.stationCount}</span>
+		</div>
+		<input
+			type="range"
+			min="5"
+			max="50"
+			step="1"
+			bind:value={stations.stationCount}
+			class="w-full h-1 rounded-full appearance-none bg-white/10 [&::-webkit-slider-thumb]:appearance-none [&::-webkit-slider-thumb]:w-3 [&::-webkit-slider-thumb]:h-3 [&::-webkit-slider-thumb]:rounded-full [&::-webkit-slider-thumb]:bg-[var(--accent-blue)] [&::-webkit-slider-thumb]:cursor-pointer"
+		/>
+	</div>
+
+	<!-- Launch velocity slider -->
+	<div>
+		<div class="flex justify-between text-xs mb-1">
+			<span class="text-[var(--text-secondary)] flex items-center gap-1">
+				Launch Velocity
+				<span
+					class="inline-flex items-center justify-center w-3.5 h-3.5 rounded-full border border-white/20 text-[8px] text-[var(--text-secondary)] cursor-help"
+					title="Current railgun tech: ~2-3 km/s&#10;Sci-fi mass drivers: 10-50 km/s&#10;Theoretical limit: ~0.01c (3,000 km/s)&#10;&#10;Higher velocity means fewer relay stations needed but more energy per launch."
+				>i</span>
+			</span>
+			<span class="text-[var(--text-primary)] font-mono">{stations.launchVelocityKms} km/s</span>
+		</div>
+		<input
+			type="range"
+			min="5"
+			max="100"
+			step="1"
+			bind:value={stations.launchVelocityKms}
+			class="w-full h-1 rounded-full appearance-none bg-white/10 [&::-webkit-slider-thumb]:appearance-none [&::-webkit-slider-thumb]:w-3 [&::-webkit-slider-thumb]:h-3 [&::-webkit-slider-thumb]:rounded-full [&::-webkit-slider-thumb]:bg-[var(--accent-orange)] [&::-webkit-slider-thumb]:cursor-pointer"
+		/>
+		<div class="flex justify-between text-[8px] text-[var(--text-secondary)] mt-0.5">
+			<span>5</span>
+			<span>50</span>
+			<span>100</span>
+		</div>
+	</div>
+
+	<!-- Station list (condensed) -->
+	{#if stations.stationNames.length > 0}
+		<div class="mt-1">
+			<div class="text-[10px] text-[var(--text-secondary)] mb-1">Active stations:</div>
+			<div class="flex flex-wrap gap-1 max-h-24 overflow-y-auto">
+				{#each stations.stationNames as name}
+					<span class="px-1.5 py-0.5 text-[9px] bg-white/5 rounded text-[var(--text-secondary)]">
+						{name}
+					</span>
+				{/each}
+			</div>
+		</div>
+	{/if}
+</div>

frontend/src/routes/+page.svelte

@@ -6,6 +6,7 @@
 	import Viewport from './(simulator)/components/Viewport.svelte';
 	import TimeControls from './(simulator)/components/TimeControls.svelte';
 	import ViewToggle from './(simulator)/components/ViewToggle.svelte';
+	import StationPanel from './(simulator)/components/StationPanel.svelte';
 
 	let wasmError = $state('');
 
@@ -14,7 +15,6 @@
 			await initWasm();
 			simulation.bodyInfos = getBodyInfos();
 			simulation.wasmReady = true;
-			// Start in Jan 2025 for a recognizable view
 			simulation.setDate(2025, 1, 1);
 			simulation.isPlaying = true;
 		} catch (e) {
@@ -37,23 +37,30 @@
 	</header>
 
 	<!-- Main content -->
-	<main class="flex-1 relative overflow-hidden">
+	<main class="flex-1 flex overflow-hidden">
 		{#if wasmError}
-			<div class="absolute inset-0 flex items-center justify-center">
+			<div class="flex-1 flex items-center justify-center">
 				<div class="bg-red-900/50 border border-red-500/30 rounded-lg p-6 max-w-md">
 					<h2 class="text-red-400 font-bold mb-2">Failed to load simulation engine</h2>
 					<p class="text-sm text-red-300/80">{wasmError}</p>
 				</div>
 			</div>
 		{:else if !simulation.wasmReady}
-			<div class="absolute inset-0 flex items-center justify-center">
+			<div class="flex-1 flex items-center justify-center">
 				<div class="text-center">
 					<div class="w-8 h-8 border-2 border-[var(--accent-blue)] border-t-transparent rounded-full animate-spin mx-auto mb-3"></div>
 					<p class="text-sm text-[var(--text-secondary)]">Initializing simulation engine...</p>
 				</div>
 			</div>
 		{:else}
-			<Viewport />
+			<!-- Viewport -->
+			<div class="flex-1 relative">
+				<Viewport />
+			</div>
+			<!-- Right sidebar -->
+			<aside class="w-64 shrink-0 p-2 bg-[var(--bg-secondary)] border-l border-white/5 overflow-y-auto">
+				<StationPanel />
+			</aside>
 		{/if}
 	</main>