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Converters, also called ISRUs (In Situ Resource Utilization), are special parts able to make fuel from raw-material. Specifically, they consume ore stored in an ore tank to make liquid fuel, oxidizer or monopropellant, requiring empty space available in an appropriate type of fuel tank. Conversion also consumes a large amount of electric charge and requires active radiator cooling to run continuously at a reasonable rate.

Producing fuel aboard a craft with a converter can allow it to have effectively unlimited delta-v, by refuelling repeatedly, so greatly extending mission range and flexibility. Conversion will generally follow, or run concurrently with, resource harvesting, with drills extracting ore from a celestial body or asteroid. On planets or moons, this will generally have been proceeded by use of resource scanners to find a location with a sufficiently high ore concentration. Although craft can also be launched pre-loaded with ore.

The conversion ratio of ore to fuel is fixed, but there is a large difference between the two converter types, and also in the base conversion rates. Conversion rate and electricity use are also very variable, being greatly effected by "thermal efficiency" (determined by the current core temperature) and by the presence and level of an engineer aboard the craft.

Converters available

Image Part Radial size Cost
Max. Temp.
Convert-O-Tron 125.png
Convert-O-Tron 125 Small 1 000 1.25 2 000 7 50 30
ISRU Converter.png
Convert-O-Tron 250 Large 8 000 4.25 2 000 7 50 30


Conversion is initiated by selecting one Italic textor moreItalic text of the options from a converter's action menu (via right clicking on the part), or bounding to an action group:

  • Start/Stop ISRU [Lf+Ox] - converts to liquid fuel and oxidizer in ratio of the need of the liquid fuel engines.
  • Start/Stop ISRU [Monoprop] - converts to monopropellant.
  • Start/Stop ISRU [LqdFuel] - converts to liquid fuel.
  • Start/Stop ISRU [Ox] - converts to oxidizer.

There must be available ore on the craft, in an ore tank that is not locked, and also space available in a fuel tank of the fuel type being produced. "Lf+Of" mode requires space for both fuel types.

Once activated, the core temperature of a converter will rise from ambient, warming up towards 100% optimal thermal efficiency at 1000K. Radiator core cooling, if available, will then begin transferring surplus heat from the core to maintain this temperature, as much as is permitted. If cooling is insufficient (always the case for the 125) the core temperature will continue to rise, eventually settling into thermodynamic balance, as heat production falls off again with decreasing thermal efficiency and passive heat dissipation to other parts and surroundings runs faster at higher temperatures. If there is no active cooling at all, the core will eventually reach the part's shut down temperature, and turn off all conversion modes, requiring manual restart.

Note that for unmanned probes (or if no engineer is on board) converter speed maxes out at 5% of nominal efficiency once you are at optimum temperature. So as an example: a Convert-O-Tron 250 set to produce Liquid Fuel will produce about .05 fuel/sec and use about 2 electric charge/sec

If electric charge on the craft is depleted the converter will stop, but then continue automatically when charge becomes available again. (Note: converters may even take priority over probe cores in a situation of inadequate electrical supply, potentially creating a deadlock where the converter can not be disabled due to limited craft control when unmanned command pods are unpowered, if there are no Kerbonauts available.)

As with drills, converters are able to run in the background, while their craft is not loaded, after switching to distant craft (or back to the KSC). Upon resuming control of the craft it will appear as if the converter had continued running, with the appropriate amount of ore consumed and fuel created. However, no charge is consumed, or cooling required (which may be exploitable).




  • ISRU added.