From 313a1a723ad3f815623d50227db50393b94b8e3e Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Thu, 26 Mar 2026 15:18:22 -0500
Subject: [PATCH] feat: thermal radiation + specific heat

---
 .../assets/config/parts/chassis.part.toml     |  3 +-
 .../assets/config/parts/hearty.part.toml      | 10 +++--
 .../assets/config/parts/housing.part.toml     |  4 +-
 crates/unified/src/config/part.rs             |  2 +
 crates/unified/src/ecs.rs                     |  5 +++
 crates/unified/src/server/heat/conduction.rs  |  5 +++
 crates/unified/src/server/heat/mod.rs         |  2 +
 crates/unified/src/server/heat/radiation.rs   | 44 +++++++++++++++++++
 crates/unified/src/server/mod.rs              |  2 +
 crates/unified/src/server/part.rs             |  7 ++-
 10 files changed, 77 insertions(+), 7 deletions(-)
 create mode 100644 crates/unified/src/server/heat/conduction.rs
 create mode 100644 crates/unified/src/server/heat/radiation.rs

diff --git a/crates/unified/assets/config/parts/chassis.part.toml b/crates/unified/assets/config/parts/chassis.part.toml
index ee79df9895f780a769efc40d27ba9634921f31e8..5e01790f758b0268b8aabf2909cbc7392b5af408 100644
--- a/crates/unified/assets/config/parts/chassis.part.toml
+++ b/crates/unified/assets/config/parts/chassis.part.toml
@@ -2,6 +2,7 @@
 name = "Chassis"
 sprite_connected = "textures/chassis.png"
 sprite_disconnected = "textures/chassis.png"
+emissivity = 1.0
 
 [physics]
 width = 50
@@ -27,4 +28,4 @@ snap = { translation = [ 0.0, -25.0, 0.0 ], rotation = 0.0 }
 [[joint]]
 id = "Left"
 target = { translation = [ -50.0, 0.0, 0.0 ], rotation = -270.0 }
-snap = { translation = [ -25.0, 0.0, 0.0 ], rotation = 0.0 }
\ No newline at end of file
+snap = { translation = [ -25.0, 0.0, 0.0 ], rotation = 0.0 }
diff --git a/crates/unified/assets/config/parts/hearty.part.toml b/crates/unified/assets/config/parts/hearty.part.toml
index 51c34700c03110a3ce9032c1708b7f7bf119c761..8b99f5a49452d5975d5d1dbec8601a8f5b9eb83b 100644
--- a/crates/unified/assets/config/parts/hearty.part.toml
+++ b/crates/unified/assets/config/parts/hearty.part.toml
@@ -2,6 +2,8 @@
 name = "Hearty"
 sprite_connected = "textures/hearty.png"
 sprite_disconnected = "textures/hearty.png"
+emissivity = 0.1
+specific_heat = 100.0
 
 [physics]
 width = 50
@@ -13,28 +15,28 @@ id = "bottom left"
 apply_force_at_local = [ -25.0, -25.0 ]
 thrust_vector = [ 0.0, 2500.0 ]
 exhaust_temperature = 1000.0
-heat_constant = 0.1
+heat_constant = 10.0
 
 [[thruster]]
 id = "bottom right"
 apply_force_at_local = [ 25.0, -25.0 ]
 thrust_vector = [ 0.0, 2500.0 ]
 exhaust_temperature = 1000.0
-heat_constant = 0.1
+heat_constant = 10.0
 
 [[thruster]]
 id = "top left"
 apply_force_at_local = [ -25.0, 25.0 ]
 thrust_vector = [ 0.0, -2500.0 ]
 exhaust_temperature = 1000.0
-heat_constant = 0.1
+heat_constant = 10.0
 
 [[thruster]]
 id = "top right"
 apply_force_at_local = [ 25.0, 25.0 ]
 thrust_vector = [ 0.0, -2500.0 ]
 exhaust_temperature = 1000.0
-heat_constant = 0.1
+heat_constant = 10.0
 
 [[joint]]
 id = "Top"
diff --git a/crates/unified/assets/config/parts/housing.part.toml b/crates/unified/assets/config/parts/housing.part.toml
index 20961b2b084d5d22de62577044168713a701d510..5ea25e5aad3dd808223bab504e3d69a3067176c9 100644
--- a/crates/unified/assets/config/parts/housing.part.toml
+++ b/crates/unified/assets/config/parts/housing.part.toml
@@ -2,6 +2,8 @@
 name = "Housing"
 sprite_connected = "textures/thruster_on.png"
 sprite_disconnected = "textures/thruster_off.png"
+emissivity = 0.2
+specific_heat = 100.0
 
 [physics]
 width = 50
@@ -13,7 +15,7 @@ id = "main"
 apply_force_at_local = [ 0, 0 ]
 thrust_vector = [ 0.0, -20000.0 ]
 exhaust_temperature = 1000.0
-heat_constant = 0.1
+heat_constant = 10.0
 
 [[joint]]
 id = "Top"
diff --git a/crates/unified/src/config/part.rs b/crates/unified/src/config/part.rs
index cdd3bdc784721f52ee540fe6e6e75a0419f0598f..c7344cb7d61ac404f72a31001b8121eda21fb142 100644
--- a/crates/unified/src/config/part.rs
+++ b/crates/unified/src/config/part.rs
@@ -21,6 +21,8 @@ pub struct PartPartConfig {
     pub name: String,
     pub sprite_connected: String,
     pub sprite_disconnected: String,
+    pub emissivity: f32,
+    pub specific_heat: f32,
 }
 #[derive(Deserialize, TypePath, Serialize, Clone, Debug, PartialEq)]
 pub struct PartPhysicsConfig {
diff --git a/crates/unified/src/ecs.rs b/crates/unified/src/ecs.rs
index fa1aa69f9a3c900a1d9e0d1378d1048788b0500e..a34849011ea98c38e600ccb9ec8b0322f98ccf1f 100644
--- a/crates/unified/src/ecs.rs
+++ b/crates/unified/src/ecs.rs
@@ -124,3 +124,8 @@ pub struct Cooler {
     pub cool_temperature: f32,
     pub heat_cooling_constant: f32,
 }
+#[derive(Component, Serialize, Deserialize, Debug)]
+pub struct Radiator {
+    pub emissivity: f32,
+    pub surface_area: f32,
+}
diff --git a/crates/unified/src/server/heat/conduction.rs b/crates/unified/src/server/heat/conduction.rs
new file mode 100644
index 0000000000000000000000000000000000000000..a6c45e1e23bbf44af0deef8569ba85c52dc458fd
--- /dev/null
+++ b/crates/unified/src/server/heat/conduction.rs
@@ -0,0 +1,5 @@
+use bevy::app::App;
+
+pub fn heat_conduction_plugin(app: &mut App) {
+
+}
diff --git a/crates/unified/src/server/heat/mod.rs b/crates/unified/src/server/heat/mod.rs
index c2212ad8ead3e69a34f46a4bb89c03292bd4e59a..02720900f92bfba340dbb77f3f765f921f20fb5b 100644
--- a/crates/unified/src/server/heat/mod.rs
+++ b/crates/unified/src/server/heat/mod.rs
@@ -1 +1,3 @@
 pub mod cooling;
+pub mod radiation;
+pub mod conduction;
diff --git a/crates/unified/src/server/heat/radiation.rs b/crates/unified/src/server/heat/radiation.rs
new file mode 100644
index 0000000000000000000000000000000000000000..0fa30700def1877adcaa7d46cfbaeb236f20729d
--- /dev/null
+++ b/crates/unified/src/server/heat/radiation.rs
@@ -0,0 +1,44 @@
+use crate::{attachment::PartInShip, ecs::{Part, Player, Radiator, Temperature}, prelude::*};
+
+const STEFAN_BOLTZMANN: f32 = 5.670374419E-8;
+const T_ENV: f32 = 4.0; // units: Kelvin
+
+pub fn heat_radiation_plugin(app: &mut App) {
+    app.add_systems(Update, part_radiation);
+}
+
+fn part_radiation(
+    time: Res<Time>,
+    parts: Query<(&mut Temperature, &Radiator, &Part)>
+) {
+    for (mut temperature, radiator, part) in parts {
+        // time for the implicit euler method
+        // e = emissivity, o = stefan-boltzmann constant, m = mass,
+        // c = specific heat, A = surface area
+        // k = (eoA)/(mc)
+        // dT/dt = -k(T^4 - T_env^4)
+        // T_env = 200.0 K
+        // T_n+1 = T_n + dt*f(T_n+1)
+        // T_n+1 = T_n - k*dt*((T_n+1)^4 - T_env^4)
+        // g(T_n+1) = T_n+1 + k*dt*(T_n+1)^4 - T_n - k*dt*(T_env)^4
+        // g'(T_n+1) = 1 + 4*k*dt*(T_n+1)^3
+        // newton's method:
+        // x_n+1 = x_n - g(x_n)/g'(x_n)
+        // where x_n is the previous guess for T_n+1
+        let initial_temp = temperature.0;
+        // temporary specific heat (c) of 1000.0
+        let k = (radiator.emissivity * STEFAN_BOLTZMANN * radiator.surface_area)
+            / (part.strong_config.physics.mass * part.strong_config.part.specific_heat);
+        let dt = time.delta_secs();
+
+        // initial guess
+        let mut next_temp = initial_temp;
+        for _ in 0..3 {
+            let g = next_temp + k*dt*next_temp.powi(4) - initial_temp - k*dt*T_ENV;
+            let g_prime = 1.0 + 4.0*k*dt*(next_temp).powi(3);
+
+            next_temp = next_temp - g/g_prime;
+        }
+        temperature.0 = next_temp;
+    }
+}
diff --git a/crates/unified/src/server/mod.rs b/crates/unified/src/server/mod.rs
index a2167557ec5d638e4a7390f0326175b5b4e39642..7191b951a250940ae05eb45a92df9f3f8f575c21 100644
--- a/crates/unified/src/server/mod.rs
+++ b/crates/unified/src/server/mod.rs
@@ -9,6 +9,7 @@ mod system_sets;
 use crate::server::earth_parts::spawn_parts_plugin;
 use crate::server::gravity::newtonian_gravity_plugin;
 use crate::server::heat::cooling::heat_cooling_plugin;
+use crate::server::heat::radiation::heat_radiation_plugin;
 use crate::server::part::part_management_plugin;
 use crate::server::planets::planets_plugin;
 use crate::server::player::player_management_plugin;
@@ -51,6 +52,7 @@ impl Plugin for ServerPlugin {
         .add_plugins(part_management_plugin)
         .add_plugins(server_thrust_plugin)
         .add_plugins(heat_cooling_plugin)
+        .add_plugins(heat_radiation_plugin)
         .configure_sets(Update, WorldUpdateSet.before(PlayerInputSet));
         //.configure_sets(Update, PlayerInputSet.before(PhysicsSet::SyncBackend));
     }
diff --git a/crates/unified/src/server/part.rs b/crates/unified/src/server/part.rs
index 0a6bd5c1b408d697ecc0a044eadd60e59204f1e2..7ccf9752b87514ce64269ea948391e14cce2cbb4 100644
--- a/crates/unified/src/server/part.rs
+++ b/crates/unified/src/server/part.rs
@@ -1,6 +1,6 @@
 use crate::attachment::{Joint, JointId, JointOf, Joints, Peer, SnapOf, SnapOfJoint};
 use crate::config::part::{CoolingConfig, CraftingConfig, JointConfig, PartConfig};
-use crate::ecs::{CanCraft, Cooler, Part, PartHandle, Temperature};
+use crate::ecs::{CanCraft, Cooler, Part, PartHandle, Radiator, Temperature};
 use crate::prelude::*;
 use bevy_replicon::prelude::Replicated;
 use crate::ecs::thruster::{PartThrusters, Thruster, ThrusterBundle, ThrusterId, ThrusterOfPart};
@@ -128,6 +128,10 @@ fn calculate_bundle(config: &PartConfig, handle: &Handle<PartConfig>) -> impl Bu
     let collider = Collider::rectangle(config.physics.width, config.physics.height);
     let mass = Mass(config.physics.mass);
     let temperature = Temperature(298.0); // note that this is 25 degrees C
+    let radiator = Radiator {
+        emissivity: config.part.emissivity,
+        surface_area: config.physics.width * config.physics.height,
+    };
 
     (
         part,
@@ -135,6 +139,7 @@ fn calculate_bundle(config: &PartConfig, handle: &Handle<PartConfig>) -> impl Bu
         collider,
         mass,
         temperature,
+        radiator,
     )
 }
 fn crafting_bundle(entity: &mut EntityCommands, config: &CraftingConfig) {