Plugin that balance reaction wheels to make RCS mandatory, also add SAS & rotation persistence (timewarp don't stop rotation)

License: Public domain

Game Version: 1.8.1

Downloads: 3,751

Author: Gotmachine

Mod Website: Forum Thread

Followers: 30

Outdated Mod

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


This plugin revisit the stock balance between the overpowered reaction wheels and RCS thrusters which are useless outside of docking situations. It does not propose a more realistic simulation of reaction wheels but is a collection of tweaks aimed at limiting their functions and balancing the gameplay.

Reaction wheels are turned into stabilizers, preventing your vessel to spin out of control and keeping it pointed at the direction you choose in the SAS autopilot. But they have a very low (and somewhat realistic) torque power when the pilot or the SAS request a pitch, roll or yaw rotation.

This mean that like in real life, most crafts always need a few RCS thrusters (and propellant) to have orientation authority, but you still get most of the playability benefits of overpowered reaction wheels.

As a side benefit, the plugin also fix the "timewarps rotation stop" stock behaviour, and introduce a few related features like keeping the vessel oriented toward the SAS selection in timewarps and when switching vessels / reloading the game.


Reaction wheels nerf

  • Reaction wheels have two different torque power, the stock one and a heavily nerfed, somewhat realistic one.
  • Nerfed torque provided on pilot or SAS rotation requests.
  • Stock torque when SAS "Stability mode" is turned on.
  • Stock torque when the vessel has reached the SAS selection (prograde, normal, target, etc).
  • Torque output is affected by the vessel angular velocity : the faster the vessel rotate, the weaker reaction wheels are.
  • Pods and cockpits built-in reaction wheels can't be controlled (they don't respond to pilot/SAS input) but still provide SAS stabilization.
  • Reaction wheels in probes cores and independent parts can be controlled.
  • Hiding of irrelevant reaction wheels right-click menu options and action groups.

Rotation persistence trough timewarp and reloading

  • Timewarping will not stop the vessel from rotating.
  • Rotation is restored after timewarping, switching vessels or reloading.
  • Rotation is not continuously calculated for unloaded (on rails) vessels, for minimal performance impact.

SAS autopilot persistence trough timewarp and reloading

  • The vessel will keep its orientation toward the SAS selection when timewarping, switching vessels or reloading.
  • The SAS selection is remembered and restored when switching vessels or reloading.


  • Features can be enabled, disabled or tweaked in the ingame "Difficulty Settings" menu.

Instructions & notes

Download & source

I highly recommend that you grab it from CKAN !

But you can also get the latest release and source from github


This requires the ModuleManager plugin to work. You can download it here



  • RCS Build Aid (Forum post) - Editor plugin to help you place your RCS thrusters efficiently.
  • RLA StockAlike (Pictures) - A light part packs featuring (among other things) some super useful small RCS thrusters, monopropellant tanks and engines.


This is my first plugin and I'm far from a skilled programmer, so the code for this may be ugly. As far as I know, it does the job and doesn't break the game. However, keep in mind that I don't really know what I'm doing. If anybody has the time to review and comment my code, I'm open to suggestions and pull requests :)


@MarkusA380 for figuring out how to make vessels rotate, you saved me a lot of time !

The whole KSP community for its awesomeness !


This masterful work of art is released under the unlicense.

So public domain, feel free to do anything, especially updating this plugin if I'm not around.

Known bugs and glitches

  • Getting out of timewarps with the SAS direction hold activated input a large roll "kick", most visible at high timewarp levels. I tried a lot of things to find out why this happen or fix it, and failed.
  • When switching to an unloaded vessel with its SAS in "target", "antitarget" or "maneuver" mode, the orientation change is applied a few frames after the vessel is unpacked, leading to the rotation event being visible to the player. Won't fix as this is minor, purely cosmetic and fixing would require large modifications.

Realism notes

The way reaction wheels work with this plugin isn't realistic. This said, in lowering their torque output to realistic values for maneuvering, this plugin make the playstyle a lot closer to the reality without cutting too much on playability. In real life, reaction wheels and control moment gyroscopes (CMR) can provide only very small amounts of torque. For example, each CMR on the ISS is rougly 1.2 meter wide, weight about 280 kg (source) and provide only 0.258 kNm of torque (source). Now compare that to the 5 kNm provided by the 0.625m, 50 kg small reaction wheel in KSP.

Loading changelog...

Stats for MandatoryRCS

Downloads over time

Downloads per version

New followers per day

Top Referrers


Export Raw Stats

Export Downloads

Export Followers

Export Referrals

Raw stats are from the beginning of time until now. Each follower and download entry represents one hour of data. Uneventful hours are omitted.