Mk-55 "Thud" Liquid Fuel Engine

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Mk-55 "Thud" Liquid Fuel Engine
Part image
Liquid fuel engine by
Rockomax Conglomerate

Radial size Radial mounted
Cost (total) 820.00 Funds
Mass (total) 0.90 t
Drag 0.2
Max. Temp. 2000 K
Volume  ?
Impact Tolerance 7 m/s
Research Advanced rocketry.png Advanced Rocketry
Unlock cost 3 500 Funds
Since version 0.16
Part configuration liquidEngineMk55.cfg
Liquid fuel engine
Maximum thrust (1 atm) 108.20 kN
(vacuum) 120.00 kN
Isp (1 atm) 275 s
(vacuum) 305 s
Fuel consumption 8.02 Units of fuel/s

Thrust vectoring 8 °
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 Mk-55 "Thud" Liquid Fuel Engine is a radially mounted liquid fuel rocket engine.

Product description

After an intensive search for an engineer crazy enough to plan and build a revolutionary new engine type, researchers turned to renowned engineer Eumon Kerman, one of the top minds in the industry. He failed miserably at the job, and this is what we ended up with. Hey, at least it works well with other large (Rockomax) engines when you want more control. Sorry, no combo deals.

Rockomax Conglomerate


The Thud is a liquid fuel engine with thrust vector control that allows efficient control of the rocket during descent and landing. The Thud is fairly low-thrust. This is offset by its comparatively low weight, however. The engine has a thrust-to-weight ratio comparable to the LV-T45 "Swivel" Liquid Fuel Engine.

The low thrust and radial mounting makes a single Thud unsuitable as a main engine on most lower stages, but it can be used to augment other engines. A common use of this engine is in lander designs, as it eliminates the need to have a vulnerable engine in an easily-damaged position. The Isp of this engine is adequate, being 275 s at 1 atm and 305 s in vacuum, not far behind the LV-T30 "Reliant" Liquid Fuel Engine and LV-T45; however, it is still greatly inferior to dedicated vacuum engines, such as the LV-909 "Terrier" Liquid Fuel Engine and the RE-L10 "Poodle" Liquid Fuel Engine.

Additionally, landing legs can be mounted directly on these engines. This is an advantage shared with other radial engines: the LV-1R "Spider" Liquid Fuel Engine, the 24-77 "Twitch" Liquid Fuel Engine and the O-10 "Puff" MonoPropellant Fuel Engine.

Like the Twitch, this engine has a respectable gimbal range of 8 degrees.

Contrary to the product description, it can indeed use fuel from rocket fuel tanks that use non-Rockomax engines as well as ones from that company.


  • The Thud bears a slight resemblance to the Space Shuttle's Orbital Maneuvering System (OMS) thrusters. However, besides obvious coloration differences, the Thud uses liquid fuel and oxidizer, unlike the real life OMS thrusters which burned hypergolic bipropellant fuel.


Appearance before 1.0.5
  • Remodeled and retextured
  • Description changed
  • Cost reduced from 850 to 800, Isp increased from 290 vacuum / 320 atmosphere to 360 vacuum / 320 atmosphere, gimbal range increased from 3° to 5°.
  • Description changed
  • Mass reduced from from 1.5 to 0.9, gimbal range increased to 3°, Isp curve changed from 330 vacuum/280 atmosphere to 320 vacuum/290 atmosphere, heat production increased from 300 to 350.
  • Renamed 'Mark 55 Radial mount engine' to 'Rockomax Mark 55 Radial Mount Liquid Engine' (Currently Mk-55 "Thud" Liquid Fuel Engine)
  • Thrust increased from 80 kN to 120 kN.
  • Manufacturer changed from Jebediah Kerman's Junkyard and Spaceship Parts Co. to Rockomax Conglomerate.
  • Initial Release