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gotmachine/KSP_RessourceFlowMode_breakdown.md

Last active June 26, 2025 14:27
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KSP RessourceFlowMode breakdown
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KSP_RessourceFlowMode_breakdown.md

Flow modes

There are 4 ways a resource request from a specific part is handled. The ResourceFlowMode enum has more values, but there is no difference between some of them.

NO_FLOW

  • Only the resources on the part the request originate from can be reached
  • The resource can only be used if flowState is true

ALL_VESSEL / ALL_VESSEL_BALANCE

  • The request will reach all parts on the vessel, excepted those for which the resource flowState is false
  • The request is split evenly between all reached parts able to fullfill the request (not empty if pulling or not full if pushing)

STAGE_PRIORITY_FLOW / STAGE_PRIORITY_FLOW_BALANCE

  • The request will reach all parts on the vessel, excepted those for which the resource flowState is false
  • At a given time, the request will only reach parts of the same priority, starting with those having the highest priority
  • It will move on to parts of a lower priority only once all parts of higher priority are empty (if pulling) or full (if pushing)
  • The request is split evenly between all currently reached parts able to fullfill the request (not empty if pulling or not full if pushing)

Note on priorities :

  • The game automatically assign the same priority to all parts belonging to a same stage.
  • A stage here refer to a set of parts separated by a staged decoupler. If the decoupler isn't staged, it is ignored.
  • The crossfeed setting of the decoupler is ignored.
  • The assigned priority depends on the order of the stage in staging list. First stages get the highest priorities.
  • Priorities can be overridden by the user on a per-part (but not per-resource) basis using the "priority offset" button in the PAW.

STACK_PRIORITY_SEARCH / STAGE_STACK_FLOW / STAGE_STACK_FLOW_BALANCE

  • The request can only reach parts connected to the requesting part and not separated by a "no crossfeed" rule.
  • Crossfeed between parts is disabled by being connected to a part that either :
    • Disable crossfeed by itself, like decouplers, some structural parts, wings...
    • Has an attach node (can be a stack or surface node) for which crossfeed is disabled. As far as I can tell, this isn't used anywhere.
  • Amongst all parts that can be reached, this use the same rules as for STAGE_PRIORITY_FLOW

Usage

The default ResourceFlowMode for a resource is primarily set at the resource definition level. However, a resource request can be done with any flow mode. For example, it is possible to define an alternative resourceFlowMode in the PROPELLANT node of a ModuleEngine or a ModuleRCS, or an alternative FlowModein theINPUT/OUTPUT_RESOURCEof aBaseConverter`.

A note on fuel ducts

The only thing a fuel duct is doing is creating an additional one-way connection between the parts it is attached to. The intended usage is in conjunction with the STACK_PRIORITY_SEARCH mode. If you place a fuel duct so that it cross two stages separated by a decoupler, this effectively bypass the "no crossfeed" rule as far as the STACK_PRIORITY_SEARCH rules are concerned, but only in one way. One stage will draw from the other (assuming priorities are set adequatly), but the other won't be able to.

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