Jet engine

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A jet engine from KSP 0.18

A jet engine is an air-breathing engine which uses onboard liquid fuel and combusts it with the oxygen drawn from the atmosphere. Due to the lower air pressure at higher altitudes its thrust output varies accordingly.

Technically, any rocket engine is also a jet engine as it forms a high-speed jet of reaction mass. But for KSP players, the term is limited to engines dependent on intake air.


Unlike rocket engines, a jet draws oxygen from the atmosphere rather than taking it from an on-board tank. This is represented in-game by a much lower rate of fuel consumption. Depending on the aircraft, jet engines can produce thrust at altitudes greater than 20 km. Jet engines do not perform in the same manner as rocket engines. Since Jet engines rely on a turbine to compress fuel and atmosphere together in order to produce thrust, it takes time to change speed. Also if the throttle or air flow are too low the engine will stall. By contrast, rocket engines give instant response to control input.

The flame out effect on a Basic Jet Engine

As of version 0.18 jet engines require intake air to run, provided by air intakes. Jet engines don't consume oxidizer, so the use of liquid fuel tanks is very wasteful because they come with an full oxidizer tank adding additional mass. When the intake air level isn't checked periodically a jet engine tends to flame out and suddenly doesn't generate any thrust. As this may happen unevenly it can cause severe spinning and potential loss of the craft.

One large difference from the jet engines compared to conventional rocket engines is, that the thrust also depends on the velocity relative to the atmosphere around. Starting with the (nominal) stationary value, thrust starts rising with additional speed, although the effect is only of minor impact at the J-33 "Wheesley". However, as more thrust most often leads to more velocity ( leading to more thrust ...) this behaviour should be considered at the more advanced engines, as it can easily lead to a rapid unscheduled disassembly. At a certain speed (the design speed of the engine) peak thrust is reached, from where on it decreases with additional velocity. At the maximum speed of the engine, it stops putting out thrust, resulting in a shutdown.

the velocity and atmosphere curves of the jet engines
Part Velocity curve(s) Atmosphere curve(s)

J-20 "Juno"

20.0 kN

J-20 Juno Basic Jet Engine velocity curve-temp.png
J-20 Juno Basic Jet Engine atmosphere curve-temp.png

J-33 "Wheesley"

120.0 kN

J-33 Wheesley Turbofan Engine velocity curve-temp.png
J-33 Wheesley Turbofan Engine atmosphere curve-temp.png

J-404 "Panther"

Dry Mode:
85.0 kN
Wet Mode:
130.0 kN

J-404 Panther Afterburning Turbofan velocity curves-temp.png
J-404 Panther Afterburning Turbofan atmosphere curves-temp.png

J-X4 "Whiplash"

130.0 kN

J-X4 Whiplash Turbo Ramjet Engine velocity curve-temp.png
J-X4 Whiplash Turbo Ramjet Engine atmosphere curve-temp.png
J-90 Goliath Turbofan Engine.png

J-90 "Goliath"

360.0 kN

J-90 Goliath Turbofan Engine velocity curve-temp.png
J-90 Goliath Turbofan Engine atmosphere curve-temp.png
Rapier Engine 01.png

CR-7 R.A.P.I.E.R.

105.0 kN

CR-7 R.A.P.I.E.R. Engine velocity curve-temp.png
CR-7 R.A.P.I.E.R. Engine atmosphere curve-temp.png

Isp of all jet engines is unaffected by speed and height, which is different from pre 1.0 behaviour as well as from rocket engines. Thus, the fuel consumption varies according to thrust output.


  • Provides excellent fuel efficiency within an atmosphere
  • All current jet engines provide thrust vectoring for greater maneuverability
  • Excellent power to weight ratio


  • Cannot be used outside of an atmosphere that contains oxygen. In current version, it means they only function on Kerbin and Laythe.
  • Thrust output changes depending on speed
  • Engine requires time to spool up to maximum thrust potential

Available jet engines

Image Part Radial size Cost
Max. Temp.
TWR Fuel
(Units of fuel/s)
(Air unit/s)
Isp (s) TVC
J-20 "Juno" Basic Jet Engine Tiny 450 0.25 2 000 7 50 20.0 Mach 0
20.6 Mach 1.3
8.16 Mach 0
8.40 Mach 1.3
0.064 1.402 6 400 No
J-33 "Wheesley" Turbofan Engine Small 1 400 1.5 2 000 7 50 120.0 Mach 0 8.16 Mach 0 0.233 29.601 10 500 Yes
J-404 "Panther" Afterburning Turbofan Small 2 000 1.2 2 000 7 50 85.00 Mach 0
107.89 Mach 1.75 /
130.00 Mach 0
219.48 Mach 2.5
7.22 Mach 0
9.17 Mach 1.75 /
11.05 Mach 0
18.65 Mach 2.5
0.193 /
7.705 /
9 000 /
4 000
10.0 No
J-X4 "Whiplash" Turbo Ramjet Engine Small 2 250 1.8 2 000 7 50 130.00 Mach 0
386.66 Mach 3.0
7.36 Mach 0
21.90 Mach 3.0
0.663 5.303 4 000 1.0 No
J-90 Goliath Turbofan Engine.png
J-90 "Goliath" Turbofan Engine Radial mounted 2 600 4.5 2 000 7 50 360.0 Mach 0 8.16 Mach 0 0.583 132.273 12 600 Yes
Rapier Engine 01.png
CR-7 R.A.P.I.E.R. Engine[Note 1] Small 6 000 2.0 2 000 20 50 105.00 Mach 0
465.64 Mach 3.75
5.35 Mach 0
23.74 Mach 3.75
0.669 4.015 3 200 3.0 No
  1. The R.A.P.I.E.R. Engine is a combination of liquid fuel and jet engine. Only the jet engine properties are shown.

See also