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LFB KR-1x2 "Twin-Boar" Liquid Fuel Engine

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LFB KR-1x2 "Twin-Boar" Liquid Fuel Engine
Part image
Liquid fuel engine by
Radial size Large
Cost (total) 17 000.00 Fund
(dry) 14 062.40 Fund
Mass (total) 42.50 t
(dry) 10.50 t
Drag 0.2
Max. Temp. 2000 K
Impact Tolerance 20 m/s
Research Heavier rocketry.png Heavier Rocketry
Unlock cost 65000 Fund
Since version 0.23.5
Part configuration Size2LFB
Testing environments
On the surface ✓ Yes
In the ocean ✓ Yes
On the launchpad ✓ Yes
In the atmosphere ✓ Yes
Sub orbital × No
In an orbit × No
On an escape × No
Docked × No
Test by staging ✓ Yes
Manually testable ✓ Yes
Liquid fuel engine
Maximum thrust (1 atm) 1 866.67 kN
(vacuum) 2 000.00 kN
Isp (1 atm) 280 s
(vacuum) 300 s
Fuel con­sumption 135.78 units of fuel/s

Thrust vectoring 1.5 °
Liquid fuel tank
Liquid fuel 2 880 units of fuel
Oxidizer 3 520 units of fuel

The LFB KR-1x2 "Twin-Boar" Liquid Fuel Engine is a liquid fuel tank and a liquid fuel engine. Usually only solid rocket boosters using solid fuel contain both, because solid fuel can't be transferred. Unlike solid rocket boosters this liquid fuel booster can run longer by pumping additional liquid fuel and oxidizer to the part. It is also throttleable, both by the main throttle and a thrust limiter tweakable. Minimum thrust required for booster to lift its own weight is 17.5%.

The LFB KR-1x2 might be a reference to the Advanced Boosters, a future Space Launch System Block 2 component.

This booster contains two engines at the bottom which are added radially, so the base of the booster is wider than a usual large tank. It also does not allow any parts to be attached below it. It contains the same amount of fuel as the Rockomax Jumbo-64 Fuel Tank (2880). The thrust is higher than the Rockomax "Mainsail" Liquid Engine and is thus the most powerful large-sized engine. However, its Isp is slightly (5-10 s) lower than that of the Mainsail at all altitudes.

The LFB KR-1x2 is the only part that is simultaneously a liquid fuel tank and engine.

Product description

This liquid fuel booster system is a very purposeful piece of engineering. Instead of relying on single engines or solid rocket boosters, the KR-1x2 employs two modified KR-1 engines, fed by a built-in fuel system, as the source of its immense lifting power. All that self-contained goodness comes at the cost of not having a mounting point for its underside, and not being quite as efficient as dedicated engines. It also comes at quite a literal cost as well.

Kerbodyne 0.24


  • Changed cost (5900 -> 16400), reduced Isp from 320-360 s to 290-340 s, changed description.
  • Initial release