SIMPLEX Propulsion

Adjusts engine atmospheric performance, fuel ratios and ISRU capabilities to give a more unique playthrough.

License: CC-BY-NC-SA

Game Version: 1.6.1

Downloads: 702

Author: theJesuit

Mod Website: Forum Thread

Followers: 4

Outdated Mod

This mod is not known to work with the latest version of Kerbal Space Program. Proceed with caution.

Information Changelog Stats

theJesuit is pleased to present:

SIMPLEX Propulsion


This is a standalone mod, or can be used with SIMPLEX TechTree, SIMPLEX Resources, SIMPLEX Living, or any combination.

This mod affects the performace of engines in atmosphere only. Vacuum performace remains unchanged. It's primary purpose is to require 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 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 the user's discretion.

Fuel Ratios and ISRU

Engines now utilise a 3:1 mix of Oxidizer:LiquidFuel.

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

The Small ISRU will now only make Oxidizer.

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

Version 1.0.20190318 for Kerbal Space Program 1.6.1

Released on 2019-03-17

Initial Release 1.0.20190318

Compatible with * Stock Tech Tree or SIMPLEX TechTree 1.8 and beyond * Stock Ore or SIMPLEX Resources 1.3 and beyond * SIMPLEX Living 1.1 and beyond


  • Contains the nerf reducing atmospheric performance of all engines at sea level to 70%. The curve line is made steeper for all engines as well. This performance nerf is also native to the SIMPLEX TechTree if you have used this is the past.


  • Contains a ratio change to rocket fuels, and ISRU changes
  • Inspired by SAFIRE by forum user @riocrokite (not currently compatible)
  • Stock based tanks modules have ratios adjusted
  • Tanks for Near Future Construction with B9PartSwitch have been adjusted
  • SmallISRU only bakes Oxidiser (with no heat)
  • ISRU will create all fuels - but with no heat
  • ISRU compatible with Stock Ore, or SIMPLEXResources


  • Additional sub tech tree nodes containing part upgrades to increase the atmospheric performance.
  • Two 'Blocks' per engine increasing performance to 80% stock and 90%
  • Upgrade nodes cost 3/5 of main node.
  • Where manufacturers release several engines in one tech tree node, the block upgrade applies to all that manufacturer's engines. Separate manufactures have separate block upgrades.
  • only engines designed for kerbin lifting are affected as vacuum performance for engines is always the same as stock.

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