S3 KS-25 "Vector" Liquid Fuel Engine

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S3 KS-25 "Vector" Liquid Fuel Engine
Part image
Liquid fuel engine by

Radial size Small, Radial mounted
Cost (total) 18 000.00 Funds
Mass (total) 4.00 t
Drag 0.2
Max. Temp. 2000 K
Volume  ?
Impact Tolerance 22 m/s
Research Tech tree very heavy rocketry.png Very Heavy Rocketry
Unlock cost 115 000 Funds
Since version 1.0.5
Part configuration part.cfg
Liquid fuel engine
Maximum thrust (1 atm) 936.51 kN
(vacuum) 1 000.00 kN
Isp (1 atm) 295 s
(vacuum) 315 s
Fuel consumption 64.74 Units of fuel/s

Thrust vectoring 10.5 °
Testing Environments
On the surface Yes
In the ocean Yes
On the launchpad Yes
In the atmosphere Yes
Sub orbital Yes
In an orbit Yes
On an escape Yes
Docked No
Test by staging Yes
Manually testable Yes

The S3 KS-25 "Vector" liquid fuel engine is an exceptionally powerful liquid fuel engine with a single nozzle.

Product description

Kerbodyne's flagship engine, the KS-25 excels as a first stage engine through its high thrust-to-weight ratio and exceptional sea level efficiency. Kerbodyne engineers achieved this by running the engine in a staged combustion cycle and at extremely high chamber pressures. Special new alloys had to be invented to suppress the engine's tendency to become a bomb. The single version is designed with very durable components and high reusability, as well as higher gimbal range, but because of that is also heavier than its expendable counterpart used in first stage clusters.



The Vector is the heaviest and most powerful 1.25m engine by far, with a mass and thrust between that of the 2.5m "Skipper" and "Mainsail" engines. It also has a relatively high thrust to weight ratio. The engine, along with its four-nozzle counterpart, the S3 KS-25x4 "Mammoth" Liquid Fuel Engine, has moderate efficiency in vacuum and the highest specific impulse at sea level for any liquid fuel engine, making it an effective engine for first stages and SSTO vehicles.

Unusually, the engine is both node- and surface-attachable. The defining feature of the engine is an extremely large gimbal range of 10.5°. These advantages are somewhat offset by its comparatively high tech requirements and cost.

It is recommended that the gimbal be reduced or locked outright on lighter craft with SAS enabled, or the gimbal can easily tear the craft apart.


  • The name KS-25 and 10.5° gimbal are references to the Space Shuttle Main Engines which are also named RS-25 and have a 10.5° gimbal range. The SSME namesake is likewise shown in that the part files are named variants of "SSME".
  • The Vector's manufacturer, Kerbodyne, is also a reference to the SSME's manufacturer, Rocketdyne.


  • Initial release