Heat and radiators
A radiator is a fin that sheds a ship's waste heat into space. It is the only way a ship in vacuum can get rid of heat for good.
38 numbers, 6 with an outside source
- A0 numbers at grade A
- B2 numbers at grade B
- C1 numbers at grade C
- D3 numbers at grade D
- E32 numbers at grade E
Functionality
1 topic
Waste heat
- Waste heat comes from your drive and your reactor plant, and it fills your coolant loop.
- A drive at full burn makes 1 heat a second.
- Intact radiators shed 12 heat every 20 s, and damaged ones less.
- Pumps carry 8 every 20 s into your water tank until it is warm.
- Your loop holds 32. Past that the tank boils, so water goes out as steam.
- With the tank dry the loop climbs to 64, and there the drive must go cold.
- Each gun has its own heat sink, and a gun with a full sink waits until it cools.
- The crew can swap in one of 3 spare sinks, in 10 s.
Values
38 numbers: 2 B, 1 C, 3 D, 32 E
Each value is read from the game code. Sort by any column heading, or filter by grade or by a word.
| Quantity | Value | Grade | Source | Why this value |
|---|---|---|---|---|
| Length of one fight round | 20 seconds | EAuthored | No source recorded | The game chose a fixed fight round so the menu fight and the engine fight count heat on one clock; no source sets a round length. |
| Heat the drive adds at full burn, per second (1 heat = 1 second of full drive waste) | 1 heat a second | EAuthored | No source recorded | The game defines the unit so that one heat is one second of the drive's full waste, which makes the drive add one heat each second at full burn. |
| Share of the drive's full heat that whole fins shed | 0.6 heat a second per heat of drive | DAnalogy | Atomic Rockets, heatrad, Mo/Li Heat Pipe (Radiator Types) | The page tables a molybdenum and lithium heat pipe radiator at about 469 kilowatts and 150 kilograms per square meter; the game chose a fin share that keeps the fins buildable from such panels. |
| Heat a whole set of fins sheds in one round (the index's 12) | 12 heat a round | EAuthored | No source recorded | The fin share each second times the seconds in a round, so it is arithmetic on two choices of the game and no source applies. |
| Share the tank pumps move into the water tank (1 minus the fin share) | 0.4 heat a second per heat of drive | EAuthored | No source recorded | One minus the fin share: the yard sizes the tank pumps for the burn the fins cannot carry, so it follows from a choice of the game. |
| Heat the coolant loop holds before the tank boils | 32 heat | EAuthored | No source recorded | Chosen by the game as the coolant loop size, the same for every hull; the notes mark it as authored and no source gives a loop size. |
| Heat the loop climbs to when the tank is dry; the drive goes cold here | 64 heat | EAuthored | No source recorded | The game chose a ceiling at a fixed multiple of the loop size, the point where the drive must go cold with no water left to boil. |
| Heat the active sweep adds each second | 0.25 heat a second | EAuthored | No source recorded | Chosen by the game as the heat an active sweep adds each second; the notes mark it as authored. |
| Temperature rise the tank water may take before it boils | 80 kelvin | DAnalogy | Atomic Rockets, heatrad, Combat Heat Sinks (the Attack Vector: Tactical water heat sink passage) | The page gives about 85 kelvin from room temperature to boiling for a water heat sink; the game takes a nearby span, and the notes record no reason for the exact figure. |
| Specific heat of water used for the tank | 4,180 J per kg per kelvin | BSecondary | Atomic Rockets, heatrad, Combat Heat Sinks (the Attack Vector: Tactical water heat sink passage) | The page gives the thermal capacity of water as 4.186 joules per gram per kelvin. |
| Energy to warm one kg of tank water to boiling and then boil it off | 2,594,400 J per kg | CDerived | Atomic Rockets, heatrad, Combat Heat Sinks (the Attack Vector: Tactical water heat sink passage) | Warming water at 4.186 joules per gram per kelvin plus vaporizing it at 2256 joules per gram, both on the page; the game adds the two for the tank span. |
| Share of the drive's jet power kept as heat (the unit's size) | 0.0001 share | EAuthored | Atomic Rockets, enginelist2, Nuclear Salt Water (NSWR) | Chosen by the game as the setting's one impossible number; the page quotes 99.8 percent thermal efficiency for a salt-water rocket with open-cycle cooling, far above what any fins could shed. |
| Spare heat sinks each gun carries | 3 sinks | EAuthored | No source recorded | The game chose a spare sink count as a second magazine of disposable heat sinks; coldweld asked for ammunition and disposable heat sinks. |
| Time to swap a cold sink in | 10 seconds | EAuthored | No source recorded | Chosen by the game as the time for a crew to swap a cold sink in; no source covers a crew swapping sinks. |
| Standing orders for spending a spare sink | kill zone, freely, never orders | EAuthored | No source recorded | Three standing orders for spending a spare sink, chosen by the game for play; no source applies. |
| Heat one firing puts in a gun's sink, by size | Micro 4, Light 6, Compact 9, Standard 13, Heavy 18, Superheavy 24 heat a firing | EAuthored | Atomic Rockets, spacewarship, the coilgun in the example design | A table the game chose in its first waste-heat pass, rising with gun size; the mirror gives heat for one design's coilgun shot but no table by size. |
| Seconds between firings, by size (the sink's shed rate is read from it) | Micro 5, Light 6, Compact 8, Standard 12, Heavy 16, Superheavy 22 seconds | EAuthored | No source recorded | A table of seconds between firings chosen by the game for play; the gun pages of the mirror give no cycle time for a mount. The sources are silent on this figure. |
| Firings a rail gun's sink takes before the gun must wait | 10 firings | DAnalogy | Atomic Rockets, spacewarship, the coilgun in the example design | One example coilgun design on the page carries coolant for ten shots, one missile wave; the game takes ten as the firings a gun's sink holds. |
| Cycles a rail gun's own fins take to shed one firing's heat | 10 cycles | EAuthored | No source recorded | Tuned by the game against bot duels; the notes record a lower trial value that left the bots winning two fights in forty. No source gives a shed rate. |
| Firings a coilgun's smaller sink takes | 6 firings | EAuthored | No source recorded | Chosen by the game so a coil has a smaller sink than the other guns, because coils are limited by coil heating and recharge; no source gives a size. |
| Cycles a coilgun's sink takes to shed one firing's heat | 14 cycles | EAuthored | No source recorded | Chosen by the game so a coil's sink sheds more slowly than the other guns; no source gives a coil cooling time. |
| Seconds of fire a cartridge gun's barrel takes | 10 seconds | EAuthored | Atomic Rockets, sidearmintro, the paragraph on guns heating in vacuum | Chosen by the game as the seconds of fire a cartridge gun's barrel takes; real autocannon fire in short bursts, but the mirror gives no figure. The sources are silent on this figure. |
| Seconds a cartridge gun's barrel needs to cool one second of fire | 3 seconds | EAuthored | Atomic Rockets, sidearmintro, the paragraph on guns heating in vacuum | Chosen by the game as the cooling time per second of fire for a cartridge barrel; the page says only that a gun in vacuum takes much longer to cool. The sources are silent on this figure. |
| Heat one evasive burn puts on the hull in a fight | 10 heat | EAuthored | No source recorded | Chosen by the game as the heat cost of a hard dodge; neither the code nor the notes give a source or a measurement for the 10. |
| Aim lost while the hull is overheated | 20 points of hit chance | EAuthored | No source recorded | Chosen by the game as the harshest of its condition penalties (overheat 20, life support 15, radiation 12, fatigue 10); no source gives an aim loss for a hot gun crew. |
| Fin condition when whole, a percentage | 100 percent | EAuthored | No source recorded | The scale the game uses for fin condition, 100 whole and 0 gone; it is a unit of the game and not a measurement. |
| Fin condition when every panel is gone; the fins then shed no heat | 0 percent | EAuthored | No source recorded | The floor of the same scale; a ship keeps fighting with shredded fins, so the game does not end the fight at zero. |
| Fin condition at or below which the fins count as crippled | 40 percent | EAuthored | No source recorded | Chosen by the game as the line where the enemy aims elsewhere and the gauge warns; the same 40 as every vital system uses. |
| Heat pipe panels on a hull's fins | 8 panels | EAuthored | No source recorded | Chosen by the game as eight panels on two fins in one plane, so a hole kills only the pipes it crosses; the mirror gives no panel count for a warship. |
| Heat a molybdenum and lithium heat pipe radiator sheds, per square meter | 469,000 watts per m^2 | BSecondary | Atomic Rockets, heatrad, Mo/Li Heat Pipe (Radiator Types) | The page names the molybdenum and lithium heat pipe as the radiator with the largest capacity, 469 kilowatts of heat per square meter, and the game uses that figure as stated. |
| Gun caliber by mount size (sets how wide a hole is against a fin panel) | Micro 0.02, Light 0.04, Compact 0.07, Standard 0.11, Heavy 0.16, Superheavy 0.22 meters | EAuthored | No source recorded | The six gun sizes of the game catalog, 20 to 220 millimeters; the same table as the ammunition module, written twice in the code, so a change must reach both. |
| Panels a drone strike on the fins cuts at the root | 3 panels | EAuthored | No source recorded | Chosen by the game so a drone that picks out the fins takes a large part of the cooling; no source gives a drone strike. |
| Share of its usual hull damage a shot at the fins still does | 0.2 share | EAuthored | No source recorded | Chosen by the game so a shot at the fins barely dents the hull; no source applies. |
| Chance an ordinary hull hit also reaches a fin | 0.25 share | EAuthored | Atomic Rockets, heatrad, Combat Radiators (the Achilles Heel passage) | Chosen by the game so a long fight can cost both sides cooling unasked; the mirror says only that fins are hard to armor, and gives no chance. The sources are silent on this figure. |
| Chance an enemy aims at the fins in one volley | 20 percent | EAuthored | Atomic Rockets, heatrad, Combat Radiators (the Achilles Heel passage) | Chosen by the game as the odds a hostile aims at the fins, never once they are crippled; the mirror says fins are the likely first target but gives no chance. The sources are silent on this figure. |
| The same chance against a well-plated target | 45 percent | EAuthored | No source recorded | Chosen by the game higher than the plain chance, because a shot at the fins ignores armor and a well-plated target is the one to cook. |
| Heat one active cooling dump vents | 18 heat | EAuthored | Atomic Rockets, spacewarshipart, Heat Radiators and the multi-mode reactor passage | Chosen by the game as a dump that beats intact fins; the mirror describes open-cycle cooling that dumps coolant overboard, and gives no rate for a ship of this size. The sources are silent on this figure. |
| Active cooling dumps a ship carries | 3 dumps | EAuthored | No source recorded | Chosen by the game; unlimited dumps made wrecked fins cost nothing, and three dumps bite only the long fights. |
Real-world basis
8 points
- A ship in vacuum has no air or water around it to carry heat away.
- So heat leaves a ship only as light, from a hot surface called a radiator.
- A radiator sheds more heat the hotter it runs, and the gain grows with the fourth power of its temperature.
- Every engine and generator wastes heat, and a machine that turns heat into power adds more waste of its own.
- A fin is large and thin, so one hit can cripple it, and that makes radiators the weak point of a warship.
- A warship can carry a heat sink instead: a cold block, such as ice, that melts as it takes heat in.
- A sink holds only a few minutes of heat, so it buys time for a fight and does not end the need for fins.
- Boiling water carries away a great deal of heat for its mass, so a ship can burn its water as a last resort.
Game and reality differences
6 points
- The game keeps heat in one unit, a point equal to one second of the hull's full drive waste. Real radiators are rated in watts per square meter. The reason is one model for both fights.
- The game's fins are a flat 0.6 of drive heat for every hull, not a computed area. Damage to the fins cuts it.
- The coolant loop is the tank, and the tank is the ship's own propellant water. Burning water as propellant leaves tank warmth unchanged, since warmth is stored as a share.
- Fins act before the pumps, so a quiet plant keeps a cold tank for a fight. A first draft pumped first and the tank was full when needed.
- A gun's sink sheds into the ship through its own small fins, not into the loop. The mirror describes a sink that is pumped out or boiled off, so the game's shed rate is a simplification.
- The menu fight's heat on the hull was replaced by a sink per gun on 2026-10-02, at coldweld's choice.
Source absences
7 points
- Atomic Rockets does not provide values for the following:
- Heat loop size. 32 points is authored.
- Heat loop ceiling. 64 points is authored.
- Share of drive power a ship keeps as heat. The share is authored, and it is the setting's one impossible number.
- Fin share of the drive's heat. 60% is authored. A code comment cites heat-pipe panels at 10 to 34% of hull mass, unverified.
- Firings a heat sink takes. The page's coilgun carries coolant for 10 shots. Sink shed rates are authored.
- Spare sink swap by a crew. 10 seconds and 3 spare sinks are authored.
- Atomic Rockets figure not used:
- A megawatt boils a ton of water in under seven minutes (Combat Heat Sinks). At 2,594,400 J per kg, one megawatt takes about 43 minutes.
Sources
6 documents
- Atomic Rockets, heatrad, Radiator Details (Stefan-Boltzmann law): Radiated power equals area times emissivity times the Stefan-Boltzmann constant times temperature to the fourth power, with space taken as zero kelvin. A hotter radiator needs far less area and mass. (all uses)
- Atomic Rockets, heatrad, Combat Radiators (the Achilles Heel passage): Drives, power plants and most weapons make huge waste heat, and radiators are hard or impossible to armor, so they are likely the first thing an enemy shoots. ""Achilles Heel" of combat spacecraft are the heat radiators" (all uses)
- Atomic Rockets, heatrad, Sikon, Combat Heat Sinks: A warship can pump heat into a cold block of phase change material, such as ice, which absorbs heat by melting. It stores only a few minutes of heat, so it puts a time limit on a fight. (all uses)
- Atomic Rockets, spacewarship, the coilgun in the example design: A coilgun makes waste heat too fast for a radiator to take it directly, so each shot's heat goes first into a heat sink (there, boiling coolant). The page gives 413 MJ of heat a shot and coolant for 10 shots. "It must be transferred to a heat sink first" (all uses)
- Atomic Rockets, thermodynamics, the heat radiator Achilles heel passage and the thermocouple answer: Heat cannot be destroyed, only moved, and making power from heat adds waste heat. Radiators are therefore the fragile price of any power plant. (all uses)
- Atomic Rockets, spacewarshipart, Heat Radiators and the multi-mode reactor passage: Burst power is cooled by open-cycle cooling that dumps coolant overboard, while decay heat goes to radiators. The page says open-cycle wastes coolant at an alarming rate. (all uses)