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SIMPLEX Propulsion

A mod that causes the atmospheric performance of all engines, and offers more natural fuel ratios.

DOWNLOAD at Spacedock


  • Module Manager (not included).


  • Download from Spacedock (or install from CKAN)
  • Ensure that Module Manager .dll is present in the Gamedata folder (not provided)
  • Extract to Gamedata so that the folder layout looks like Gamedata/AngleCanMods/SIMPLEXPropulsion
  • There will be three .cfg files.
    - SIMPLEXPropulsionEngines.cfg contains the engine changes.
    - SIMPLEXPropulsionFuel.cfg contains the fuel ratios and ISRU changes.
    - SIMPLEXPropulsionUpgrades.cfg contains the Partupgrades and TechTree changes.
  • The Fuel or Upgrade files could be deleted if you don't want to use them.  Don't delete the Engines file.


Like all SIMPLEX mods, this can be installed by as a standalone mod.

Installed as a standalone mod

  • The PartUpgrades will creates nodes with the Stock Tech Tree, and as such the Community Tech Tree as well.
  • It changes the ISRU rates/ratios for converting Ore to LiquidFuel, Oxidizer, but in keeping with the stock processes (please read more below).

Installed with SIMPLEX TechTree

  • The PartUpgrades will creates nodes appropriately.

Installed with SIMPLEX Resources

  • The ISRU will create Oxidizer from NaturalOre, and LiquidFuel from HydrateOre, and MonoPropellant requiring both.

Installed with SIMPLEX Living

  • The ISRU processes (with or without SIMPLEX Resources) will be handled by Kerbalism.



The performance of engines in atmosphere only. Vacuum performance remains unchanged. It's purpose is an attempt at forcing the creation of three stage rockets to take off from Kerbin, but retaining the STOCK feel of KSP once in vacuum.

The performance at sea level on Kerbin is 70% of stock values. Vacuum performance is unaffected and so the performance improvement as you ascend is far greater rate than stock as it normalises.


Engine Block Upgrades

Engines that are designed to be used to launch rockets from Kerbin (Swivel, Reliant, Skipper etc.) have Part Upgrades to improve their atmospheric performance to 80% or 90% stock.

Vacuum engines (such as Terrier or Poodle), do not have upgrades.

These upgrades are available using the Stock Tech Tree,the Community TechTree addon or SIMPLEX TechTree.

The cfg file that contains these can be removed at user's discretion.


Fuel Ratios and ISRU

Engines now utilise a 3:1 mix of Oxidizer:LiquidFuel (stock is 1.1:0.9).  This is more in line with a balance between Oxidizer:RP-1 (2.56:1) and Oxidizer:Methane (3.2:1).

ISRU rates have been adjusted for Stock Ore, or SIMPLEX Resources.

The Small ISRU will now only make Oxidizer.

The reason Oxidizer is easier to produce is that in real life, hydrogen to produce fuel is scarcer.  Suggested ISRU methods recommend taking hydrogen to produce the furl on site.  Oxidizer seems to be able to be produced anywhere.  See the bottom of this post for a link for a more in depth discussion by riocrokitee.

The cfg file that contains these can be removed at user's discretion.



@Jimbodiah for the inspiration with the config he made for SSRSS.  Check it out here: https://forum.kerbalspaceprogram.com/index.php?/topic/169534-12x-13x-simple-rss-patch/

@riocrokite for inspiration from SAFIRE and the persuasive work he did with ratios.  Check out his mod and explanations here: https://forum.kerbalspaceprogram.com/index.php?/topic/181591-16x-safire-stockalike-adjustments-to-fuels-isru-ratios-and-engines-21-01-2019/.



Edited by theJesuit
Completing the OP
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Hi all,

So we hit 52 downloads over night (gosh CKAN helps :). Thanks for giving it a go.

I would be keen to know whether people are playing with other Simplex Mods or opt to not use the upgradesign or fuel ratio change.

I've noticed an issue potentially with only simplex mods AND kerbalism and not having an ability to mine NaturalOre (to bake oxidiser).  I'll look at this over the next few days.  All other combinations look good though.

So as I said, thanks for trying it out and feedback would be appreciated.  I'm happy for a PM.


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  • 3 months later...

Hi everyone,

There will be an update at some point.   I'm going to add an engine!

Theis will be a aluminium/ox throttleable (sp?) Rocket engine.  The idea being that it is to SolidFuel what LF/ox is to MonoPropellant. 

The idea being that it will be a low ISP med thrust vacuum only engine.  Suitable for lifting off the Mün.  With ISRU and SimplexResouces the fuel and Oxidizer will come from NaturalOre only.

The concept comes form a NASA study into a rocket fuel using  only Moon  abundantin eras in the regolith.  Hydrogen in a few small spots in polar craters doesn't qualify as abundant IMHO.

No ETA yet.


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