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Small Inline Reaction Wheel

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Small Inline Reaction Wheel
Part image
Stability Augmentation System by
Found lying by the side of the road
Radial size Tiny
Cost (total) 600.00 Fund
Mass (total) 0.05 t
Drag 0.2
Max. Temp. 2000 K
Impact Tolerance 9 m/s
Research Flight control.png Flight Control
Unlock cost 3200 Fund
Since version 0.7.3
Part configuration inlineReactionWheel
Pitch torque 5.0 kN·m
Yaw torque 5.0 kN·m
Roll torque 5.0 kN·m
Electricity required for torque
SAS level × None

The Small Inline Reaction Wheel (previously named Inline Reaction Wheel) is a toggleable reaction wheel that provides torque to a craft. Extra torque means that the player's spaceship will rotate faster when ordered to, resulting in a more nimble feel to the craft. The Inline Reaction Wheel is the 'Tiny' size reaction wheel. The small inline reaction wheel also seems to resemble HAL 9000 from the 1968 movie 2001: A Space Odyssey.


The placement does matter for reaction wheels. Generally speaking they can cause some problems if placed far from the center of mass. Imagine you are grabbing that point and rotating it. That is what the reaction wheels will try to do. You'll get offcenter rotation anywhere other then near the COM.

comment by C7, in his blog entry “Updated Information on SAS in 0.21.1

However, this is not actually correct with rigid spacecraft. A reaction wheel should provide the same torque regardless of placement. However, off-center reaction wheels will cause very long vehicles, especially with docking ports, to bend, which can cause instability.

Product description

The inline reaction wheel system uses a series of spinning discs that are going "Very Fast", to generate the torque necessary to control a spacecraft without wasting any propellant. Please do not attempt to service this device while it is running.


  • No longer has any SAS functionality - only provides torque
  • Renamed “Inline Reaction Wheel” into “Small Inline Reaction Wheel”
  • Resized model and radial size from small to tiny
  • Mass decreased from 0.12 to 0.05
  • Torque decreased from 8 to 5
  • Required electricity decreased from 24.0/min to 15.0/min
  • Mass decreased from 0.3 to 0.12
  • Torque decreased from 20 to 8
  • Increased torque (3 → 20)
  • Mass decreased from 0.5 to 0.3
  • Renamed from “S.A.S Module” into “Inline Reaction Wheel”
  • Mass increased from 0.07 to 0.5
  • Costs electric charge
  • New model and texture
  • (Undocumented) Mass reduced from 0.8 to 0.07, cost reduced from 2300 to 600
  • (Undocumented) Torque increased from 10 to 20, Ki/Kp/Kd changed from 1.0 / 3.0 / 5.0 to 0.0 / 5.0 / 3.5
  • (undocumented) SAS now use angular momentum instead of angular velocity - takes into account inertia momentum of the ship [1]
  • (undocumented) Tweaked Kd, Ki and Kp parameters
  • Exposed Kd, Ki and Kp parameters for tuning the SAS module
  • SAS toggle with T key
  • Initial Release