RE-M3 "Mainsail" Liquid Fuel Engine

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RE-M3 "Mainsail" Liquid Fuel Engine
Part image
Liquid fuel engine by
Rockomax Conglomerate

Radial size Medium, Large
Cost (total) 13 000.00 Funds
Mass (total) 6.00 t
Drag 0.2
Max. Temp. 2000 K
Volume  ?
Impact Tolerance 7 m/s
Research Heavier rocketry.png Heavier Rocketry
Unlock cost 38 000 Funds
Since version 0.16
Part configuration liquidEngineMainsail.cfg
Liquid fuel engine
Maximum thrust (1 atm) 1 379.03 kN
(vacuum) 1 500.00 kN
Isp (1 atm) 285 s
(vacuum) 310 s
Fuel consumption 98.68 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 RE-M3 "Mainsail" Liquid Fuel Engine is one of the heaviest and most powerful large-diameter engines among the stock parts. It is usually used to provide thrust for larger rockets and lower stages. It is typically fueled by large diameter liquid fuel tanks like the Rockomax X200-32 Fuel Tank. Prior to version 0.23.5 it was the largest engine, as well as the one with the highest thrust. Those titles, however, are now held by the S3 KS-25x4 Engine Cluster.


The Mainsail is a common choice for lifting large stacks of liquid fuel tanks into orbit and beyond, or propelling large heavy lift vehicles. As of 1.11.1, this is one of four size 2 engines in the base game. The thrust vectoring also gives it good pitch and yaw control, greatly easing first stage stability, though care must be taken to not allow S.A.S. to tear the ship apart. The thrust-to-weight ratio of this engine is excellent. The specific impulse is also fairly good, though it can still consume large amounts of fuel.

The high thrust of this engine combined with thrust vectoring can destroy poorly built rockets in the middle of ascents. Throttling down or limiting the gimbaling is often recommended. Prior to version 0.22 the Mainsail would tend to quickly explode from overheating when run on maximum throttle and placed under a Rockomax Jumbo-64 Fuel Tank. Though this has been resolved, other parts may encounter the same bug. Placing a small strut or fuel tank between the engine and the Jumbo-64 will mitigate this.

Product description

A monster of an engine for heavy lifting purposes, the Mainsail's power rivals that of entire small nations.
Appearance as of 1.3


  • New texture and variants
  • Renamed from RE-M3 "Mainsail" Liquid Engine to RE-M3 "Mainsail" Liquid Fuel Engine
  • Cost increased (850 → 5650), specific impulse increased (280-330 → 320-360)
  • heatProduction reduced from 500 to 400, as a work around to heat transfer bugs with the Jumbo-64
  • Renamed from LV-T30 Liquid Fuel Engine to Rockomax "Mainsail" Liquid Engine, thrust increased (1200 → 1500), mass decreased (7 → 6), new description
  • Initial release


The 1.9 reskin made Mainsail resembles Vulcain, albeit overpowered. In the stock included Ariane 5, the Mainsail's thrust is lowered to 73.5%