S3 KS-25x4 "Mammoth" Liquid Fuel Engine

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S3 KS-25x4 "Mammoth" Liquid Fuel Engine
Part image
Liquid fuel engine by

Radial size Extra large
Cost (total) 39 000.00 Funds
Mass (total) 15.00 t
Drag 0.2
Max. Temp. 2000 K
Volume  ?
Impact Tolerance 20 m/s
Research Tech tree very heavy rocketry.png Very Heavy Rocketry
Unlock cost 115 000 Funds
Since version 0.23.5
Part configuration part.cfg
Liquid fuel engine
Maximum thrust (1 atm) 3 746.03 kN
(vacuum) 4 000.00 kN
Isp (1 atm) 295 s
(vacuum) 315 s
Fuel consumption 258.98 Units of fuel/s

Thrust vectoring 2 °
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-25x4 "Mammoth" Liquid Fuel Engine is a size 3 liquid fuel engine. It is the most powerful (and most expensive) engine available in the game.

Product description

Kerbodyne engineers got fed up with having to contend with overly complicated staging arrays for lifting heavy payloads, and decided instead to just build a truly enormous engine of the highest efficiency. Strapping together four of Kerbodyne's KS-25 rocket motors in a single assembly, they created the largest rocket engine in production anywhere, and each KS-25 has the highest chamber pressure--the reason for four small nozzles and combustion chambers, not one big one (those kept going boom). It's certainly got the power to match its size, and although it excels in its main role as a first-stage engine, the lack of structural hardpoints on its underside makes it quite less suitable for other purposes. Its price tag also seems to match its size, in fact.



The Mammoth has the highest specific impulse at sea level of any liquid fuel engine, tied with that of its counterpart, the S3 KS-25 "Vector" Liquid Fuel Engine. This makes it an effective engine for first stages and SSTO vehicles. As noted in the product description, it is the highest-thrust single engine in the game.

There are no attachment nodes for placing additional stages beneath the engine cluster. This means that the Mammoth will almost always be found at the bottom of a vessel's first stage.

According to the part description. the engine is assembled from four S3 KS-25 "Vector" Liquid Fuel Engines. The Mammoth's Isp and thrust match this description. However, the Mammoth is one ton lighter and 46% cheaper, but has a much lower gimbal range, than four Vector engines.

After the CR-7 R.A.P.I.E.R. Engine, this is the second liquid fueled engine to use multiple nozzles. (Although the multi-nozzle RE-L10 "Poodle" Liquid Fuel Engine was introduced earlier, its two-nozzle model was not introduced until version 1.6.)


KS-25 is a reference to RS-25, the official designation of the Space Shuttle Main Engines. The part, which uses four KS-25 engines, is inspired by the main engine component of the Space Launch System, which similarly uses four RS-25 engines. The part was introduced along with several other SLS-inspired parts.


  • Cost increased from 5900 to 32400 (and made meaningful)
  • Initial release