# RTG and Stirling

Two small generators whose output is a function of **state** rather than a flat number: the
**Radioisotope Generator** fades with the half-life of its pellet, and the **Stirling Generator**
makes power from the temperature difference between a hot machine and a cold face — cooling the
machine as it does.

## Radioisotope Generator (RTG)

### How it works

Drop an **Isotope Pellet** in. The RTG consumes it, notes the moment, and from then on produces
`rtgNePerTick × 2^(−elapsed ⁄ half-life)`: **30 NE/t** fresh, 15 NE/t after 20 in-game days,
7.5 after 40, and so on. The GUI shows the current output as a percentage of fresh, the day the
pellet is on and the days left until it is spent.

Once output falls below `rtgCutoffPermille` of the fresh rate (5 % — about 4.3 half-lives, or
roughly 86 in-game days at the defaults) the pellet is **spent** and a **Spent Isotope Pellet**
appears in the output slot. If the output slot is full the RTG waits, dark, until it is emptied.
Insert the next pellet and the cycle restarts.

- Sealed and fuel-free once loaded: **no heat, no running pollution, no failure ladder**, and decay
  runs the same in every dimension — it is the generator for an airless moon base.
- Overdrive presets and Speed modules scale the output.
- Energy leaves every face; pellets are accepted on every face; spent pellets can be pulled from
  any face you set to *output* in the Side Config tab.
- Never load-shed by NeroTech's throttling.

### Recipes

| Item | Recipe |
| --- | --- |
| **Radioisotope Generator** | Iron Ingot, Nero Coil, Iron Ingot / Circuit Board, Machine Frame, Nero Coil / Iron Ingot, empty, Iron Ingot |
| **Isotope Pellet** | 1 Uranium Pellet + 4 Glowstone Dust (shapeless) |

Spent Isotope Pellets are never crafted — they come out of the generator.

### Disposing of spent pellets

A Spent Isotope Pellet is safe in a chest, but **destroying one as a dropped item pollutes**: when
the item entity is destroyed — burnt in fire, thrown in lava, dropped on a cactus, caught in an
explosion — it records a burst of `rtgSpentPelletPollution` (200) per pellet into NeroTech's
regional pollution at that spot, the same kind of burst a NeroTech fusion containment breach vents.
A stack of 64 is 64 bursts. The burst triggers on **destruction** only: water does not destroy
item entities in vanilla (a pellet dropped in the sea just floats), a pellet that despawns after
five minutes vents nothing, and falling out of the world removes the item without vanilla's
destruction hook, so that vents nothing either. The pollution is regional and never attributed to
a player.

### Config keys

| Key | Default | Range | What it does |
| --- | --- | --- | --- |
| `rtgNePerTick` | 30 | 1–10000 | Output from a fresh pellet (NE/t) |
| `rtgHalfLifeDays` | 20 | 1–365 | In-game days per halving of output |
| `rtgCutoffPermille` | 50 | 1–999 | Output (permille of fresh) below which a pellet is spent |
| `rtgSpentPelletPollution` | 200 | 0–100000 | Pollution burst per Spent Isotope Pellet destroyed as a dropped item |

## Stirling Generator

### How it works

Every tick the Stirling Generator looks at its six neighbours, finds the **hottest NeroTech-family
machine** (any NeroTech machine or NeroPower reactor) and reads how far above its ambient
temperature it is — the **gradient**. It then draws a share of that gradient as heat,
`gradient × stirlingDrawPermille ⁄ 1000` (10 %) per tick, capped at `stirlingMaxDrawPerOp` (8), and
never pulls a machine below its ambient level. Every unit of heat drawn becomes
`stirlingNePerHeatUnit` NE (15).

A **cold face** matters. If any neighbour is water, ice, packed ice, blue ice, a snow block,
powder snow or a NeroTech **Radiator**, output gets a **+50 %** bonus. Without a cold face the
usable gradient is **halved** — the engine has nowhere to reject its heat. The GUI shows the
gradient, the heat drawn last tick and whether a cold sink is attached.

**Planet efficiency.** With `planetEfficiencyEnabled` on (the default) the cold-face bonus grows
with how cold the local ambient is — NeroTech's planet ambient for that spot, which follows the
Nerospace planet (or NeroTech's `thermalAmbientByDimension` table) plus the biome:
`bonus × (1000 + clamp(−ambient × 5, 0, 1000)) ⁄ 1000`. On a cold planet at ambient −80 the +50 %
bonus becomes **+70 %** (40 % larger); at ambient 0 or warmer — the Overworld's default — it stays
+50 %; the scaling tops out at double the bonus (ambient −200 or colder). The ambient is re-read
every 200 ticks. With the key off the bonus is flat everywhere.

Because it removes heat from its neighbour, a Stirling Generator is also a **passive coolant with
a dividend**: parked against a running [Fission Reactor](Fission-Reactor.md) it lowers the
reactor's heat and pays you for it. It has no slots, no fuel, no heat of its own and no failure
ladder; presets and Speed modules scale the output.

### Recipes

| Item | Recipe |
| --- | --- |
| **Stirling Generator** | Iron Ingot, Piston, Iron Ingot / Nero Coil, Machine Frame, Piston / empty, Copper Block, empty |

### Config keys

| Key | Default | Range | What it does |
| --- | --- | --- | --- |
| `stirlingNePerHeatUnit` | 15 | 1–1000 | NE produced per unit of heat drawn |
| `stirlingMaxDrawPerOp` | 8 | 1–1000 | Hard cap on heat drawn per tick |
| `stirlingDrawPermille` | 100 | 1–1000 | Share of the gradient drawn per tick |
| `stirlingColdFaceBonusPermille` | 500 | 0–1000 | Output bonus with a cold face |
| `planetEfficiencyEnabled` | true | — | Scale the cold-face bonus with the local ambient (see above) |