diff --git a/src/world.rs b/src/world.rs
index a895f26..a24cf75 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -6,6 +6,7 @@ use bevy_xpbd_3d::prelude::*;
 use bevy_xpbd_3d::plugins::sync::SyncConfig;
 use std::f32::consts::PI;
 
+const ASTEROID_UPDATE_INTERVAL: f32 = 1.0; // seconds
 const ASTEROID_SIZE: f32 = 100.0;
 const STARS_MAX_MAGNITUDE: f32 = 5.5;
 
@@ -30,11 +31,16 @@ pub struct WorldPlugin;
 impl Plugin for WorldPlugin {
     fn build(&self, app: &mut App) {
         app.add_systems(Startup, setup);
+        app.add_systems(Startup, generate_asteroids);
         app.add_systems(Update, handle_cheats);
+        app.add_systems(Update, spawn_despawn_asteroids);
         app.add_plugins(PhysicsPlugins::default());
         app.add_plugins(MaterialPlugin::<RingMaterial>::default());
         //app.add_plugins(PhysicsDebugPlugin::default());
         app.insert_resource(Gravity(DVec3::splat(0.0)));
+        app.insert_resource(AsteroidUpdateTimer(
+                Timer::from_seconds(ASTEROID_UPDATE_INTERVAL, TimerMode::Repeating)));
+        app.insert_resource(AsteroidDatabase(Vec::new()));
 
         // Disable bevy_xpbd's position->transform sync because we have a
         // custom syncing function.
@@ -46,6 +52,18 @@ impl Plugin for WorldPlugin {
     }
 }
 
+#[derive(Resource)] struct AsteroidUpdateTimer(Timer);
+#[derive(Resource)] struct AsteroidDatabase(Vec<AsteroidData>);
+
+struct AsteroidData {
+    is_spawned: bool,
+    class: u8,
+    size: f32,
+    x: f64,
+    y: f64,
+    z: f64,
+}
+
 #[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
 pub struct RingMaterial {
     alpha_mode: AlphaMode,
@@ -74,48 +92,6 @@ pub fn setup(
     mut materials_custom: ResMut<Assets<RingMaterial>>,
     asset_server: Res<AssetServer>,
 ) {
-    // Generate a bunch of asteriods
-    let maxdist = 4;
-    let pi = PI as f64;
-    let player_x: f64 = -300000.0;
-    let player_y: f64 = 0.0;
-    let player_z: f64 = -500000.0;
-    for i in -maxdist..maxdist {
-        for j in -maxdist..maxdist {
-            for k in -maxdist..maxdist {
-                let offset: f64 = 500.0;
-                let dist: f64 = 8e3;
-                let wobble: f64 = dist/2.0;
-                let (i, j, k) = (i as f64, j as f64, k as f64);
-                let asset = match ((i+j+k) as i32) % 2 {
-                    0 => ASSET_ASTEROID1,
-                    _ => ASSET_ASTEROID2,
-                };
-                commands.spawn((
-                    actor::Actor::default(),
-                    RigidBody::Dynamic,
-                    AngularVelocity(DVec3::new(0.1, 0.1, 0.03)),
-                    LinearVelocity(DVec3::new(0.0, 0.0, 0.35)),
-                    Collider::sphere(1.0),
-                    SceneBundle {
-                        transform: Transform {
-                            scale: Vec3::splat(ASTEROID_SIZE),
-                            ..default()
-                        },
-                        scene: asset_server.load(asset),
-                        ..default()
-                    },
-                    Rotation::from(Quat::from_rotation_y(-PI / 3.)),
-                    Position::from_xyz(
-                        player_x + offset + dist * i + wobble * (j+k/pi).sin() * (k+j/pi).cos(),
-                        player_y + offset + dist * j + wobble * (k+i/pi).sin() * (i+k/pi).cos(),
-                        player_z + offset + dist * k + wobble * (i+j/pi).sin() * (j+i/pi).cos(),
-                    ),
-                ));
-            }
-        }
-    }
-
     // Generate starmap
     let sphere_handle = meshes.add(Sphere::new(1.0));
     let mut starcount = 0;
@@ -181,6 +157,74 @@ pub fn setup(
     ));
 }
 
+fn generate_asteroids(
+    mut db: ResMut<AsteroidDatabase>,
+) {
+    let maxdist = 4;
+    let pi = PI as f64;
+    let player_x: f64 = -300000.0;
+    let player_y: f64 = 0.0;
+    let player_z: f64 = -500000.0;
+    for i in -maxdist..maxdist {
+        for j in -maxdist..maxdist {
+            for k in -maxdist..maxdist {
+                let offset: f64 = 500.0;
+                let dist: f64 = 8e3;
+                let wobble: f64 = dist/2.0;
+                let (i, j, k) = (i as f64, j as f64, k as f64);
+                db.0.push(AsteroidData {
+                    is_spawned: false,
+                    x: player_x + offset + dist * i + wobble * (j+k/pi).sin() * (k+j/pi).cos(),
+                    y: player_y + offset + dist * j + wobble * (k+i/pi).sin() * (i+k/pi).cos(),
+                    z: player_z + offset + dist * k + wobble * (i+j/pi).sin() * (j+i/pi).cos(),
+                    size: ASTEROID_SIZE,
+                    class: (((i+j+k) as i32) % 2) as u8,
+                });
+            }
+        }
+    }
+}
+
+fn spawn_despawn_asteroids(
+    time: Res<Time>,
+    mut timer: ResMut<AsteroidUpdateTimer>,
+    mut db: ResMut<AsteroidDatabase>,
+    mut commands: Commands,
+    asset_server: Res<AssetServer>,
+) {
+    if !timer.0.tick(time.delta()).just_finished() {
+        return;
+    }
+
+    for asteroid in &mut db.0 {
+        if asteroid.is_spawned {
+            continue;
+        }
+        asteroid.is_spawned = true;
+        let asset = match asteroid.class {
+            0 => ASSET_ASTEROID1,
+            _ => ASSET_ASTEROID2,
+        };
+        commands.spawn((
+            actor::Actor::default(),
+            RigidBody::Dynamic,
+            AngularVelocity(DVec3::new(0.1, 0.1, 0.03)),
+            LinearVelocity(DVec3::new(0.0, 0.0, 0.35)),
+            Collider::sphere(1.0),
+            SceneBundle {
+                transform: Transform {
+                    scale: Vec3::splat(asteroid.size),
+                    ..default()
+                },
+                scene: asset_server.load(asset),
+                ..default()
+            },
+            Rotation::from(Quat::from_rotation_y(-PI / 3.)),
+            Position::from_xyz(asteroid.x, asteroid.y, asteroid.z),
+        ));
+    }
+}
+
 fn handle_cheats(
     key_input: Res<ButtonInput<KeyCode>>,
     mut q_player: Query<(&Transform, &mut Position, &mut LinearVelocity), With<actor::PlayerCamera>>,