Reaction engine

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A reaction engine is an engine that uses nothing but its onboard propellant to generate thrust. Unlike traditional air breathing jet engines, rocket engines are able to function where no oxygen is present. If there is also a combustion it is called a rocket engine.

Physics

All reaction engine work with the same principle: They propel mass out of nozzles and accelerate because of Newton's third law of motion. The difference to jet engines is that it doesn't need a surrounding atmosphere. Also it doesn't need any surface which allows them to be used everywhere.

There are four different types available in the game which all use this basic principle. Apart from RCS thrusters their controls are the same. Except for the ion engine all engines are rocket engines as they burn up fuel instead of simply accelerating it. The RCS from the EVA suit is most likely a reaction engine which expels nitrogen gas without combusting it.

Solid fuel rocket engines

→ Main article: Solid rocket booster

The most ancient type is a solid fuel rocket which is as simple as igniting a solid, self-oxidizing compound or mixture within the casing of the rocket and allowing the escaping gases to be released through a nozzle at the rear.

Advantages

  • Have a very high thrust to weight ratio.
  • Engine and fuel tank are combined in one part, lowering part count, simplifying design and improving stability, which is especially important in the early stages of a rocket launch from the surface of a planet where large amounts of more or less heavy parts and high-powered rockets cause stress both to the vessel itself and the player's computer.

Disadvantages

  • Monolithic design, must be built in one piece.
  • Cannot be throttled or switched off after ignition.
  • Once spent, they are unable to use fuel from another source of the craft.
Available solid fuel rocket engines
Solid Fuel Density is 7.5 kg/unit Mass
(t)
Fuel
(Units of fuel)
Thrust
(kN)
TWR Isp (s) Burn
(s)
Full Empty
Image Part Radial size Cost
(Funds)
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
atm vac atm vac atm vac atm vac
RT-5 White.png
RT-5 "Flea" Solid Fuel Booster Small, Radial mounted 200
(116)
1.50 0.45 2 000 7 50 140 162.91 192.0 11.07 13.05 36.92 43.51 140 165 8.8
RT-10 White.png
RT-10 "Hammer" Solid Fuel Booster Small, Radial mounted 400
(175)
3.56 0.75 2 000 7 50 375 197.90 227.0 5.66 6.50 26.91 30.86 170 195 23.7
BACC SFB.png
BACC "Thumper" Solid Fuel Booster Small, Radial mounted 850
(358)
7.65 1.50 2 200 7 50 820 250.00 300.0 3.33 4.00 17.00 20.39 175 210 42.2
SRB.png
S1 SRB-KD25k "Kickback" Solid Fuel Booster Small, Radial mounted 2 700
(1 140)
24.00 4.50 2 200 7 50 2 600 593.86 670.0 2.52 2.85 13.46 15.18 195 220 62.8
Sepratron.png
Sepratron I Radial mounted 75
(70.2)
0.1 0.0 2 000 7 50 8 13.79 18.0 19.40 25.32 112.51 146.84 118 154 5.0
FM1 "Mite" Solid Fuel Booster Tiny, Radial mounted 75
(51.0)
0.375 0.075 2 200 7 50 40 11.012 12.5 2.93 3.33 14.68 16.66 185 210 49.44
F3S0 "Shrimp" Solid Fuel Booster Tiny, Radial mounted 150
(96.0)
0.875 0.155 2 200 7 50 90 26.512 30.0 3.22 3.65 17.1 19.35 190 215 47.44
[[S2-17 "Thoroughbred" Solid Fuel Booster|]] Large, Radial mounted 9 000
(4 200.0)
70.00 10.00 2 200 10 50 8 000 1 515.217 1 700.0 2.16 2.43 15.15 17.0 205 230 79.6
[[S2-33 "Clydesdale" Solid Fuel Booster|]] Large, Radial mounted 18 500
(8 660.0)
144.00 21.00 2 200 10 50 16 400 2 948.936 3 300.0 2.05 2.29 14.04 15.71 210 235 85.9

Liquid fuel rocket engines

Liquid fuel engines are powered by a liquid propellant which is comprised of combustible liquid fuel and oxidizer. In the real world typical liquid fuels are often liquid hydrogen or kerosene, and typical oxidizers are liquid oxygen or nitrous-oxide. All engines use Bell nozzles except the only aerospike engine.

The LV-N Atomic Rocket Motor is treated by the game as a liquid fuel rocket actually would be in its own category and not a rocket engine.

Advantages

  • Fuel and oxidizer can be moved between liquid fuel tanks, which means that spacecraft with liquid fuel engines and fuel tanks are easier and more resource-efficient to refuel than vessels with solid fuel engines, which required the entire engine bay to be replaced, while liquid fuel and oxidizer can quickly be moved between two docked vessels.
  • Modular design: fuel and other components can be stored elsewhere in the craft.
  • Throttle can be adjusted depending on thrust requirements.
  • Can be switched off and re-ignited at will.
  • Many nozzles can be gimballed for thrust vectoring.
  • Efficiency largely dependent on design, with large variations. For early stages, high-output engines with low fuel-efficiency can be used to reach a low Kerbin orbit, while extremely efficient but low-power engines should be used for travelling between planets and moons to save fuel and extend the range of the craft.

Disadvantages

  • Lower power to weight ratio compared to solid rocket engines.
  • Complex design with fuel tanks and other additional components.
  • More points of possible failure such as if the parts tear apart from stress.
Available liquid fuel rocket engines
Thrust
(kN)
T/W
ratio
Max. Fuel
Consumption
(Units of fuel/s)
Isp (s) TVC
Image Part Radial size Cost
(Funds)
Mass
(t)
Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
atm vac atm vac atm vac Gimbal
(°)
LV-1R Shroud.png
LV-1R "Spider" Liquid Fuel Engine Radial mounted 120 0.02 2 000 7 50 1.79 2.0 9.14 10.20 0.141 260 290 10.0
24-77 Orange.png
24-77 "Twitch" Liquid Fuel Engine Radial mounted 230 0.08 2 000 7 50 15.17 16.0 19.34 20.39 1.125 275 290 8.0
Mk-55 Radial mount engine.png
Mk-55 "Thud" Liquid Fuel Engine Radial mounted 820 0.90 2 000 7 50 108.20 120.0 12.26 13.60 8.024 275 305 8.0
O-10.png
O-10 "Puff" MonoPropellant Fuel Engine[Note 1] Radial mounted 150 0.09 2 000 7 50 9.60 20.0 10.88 22.66 2.039 120 250 6.0
LV-1 Shroud.png
LV-1 "Ant" Liquid Fuel Engine Tiny, Radial mounted 110 0.02 2 000 7 50 0.51 2.0 2.59 10.20 0.129 80 315
48-7S Shroud.png
48-7S "Spark" Liquid Fuel Engine Tiny 240 0.13 2 000 7 50 16.56 20.0 12.99 15.69 1.275 265 320 3.0
LV-909 Shroud.png
LV-909 "Terrier" Liquid Fuel Engine Small 390 0.50 2 000 7 50 14.78 60.0 3.01 12.24 3.547 85 345 4.0
LV-T30 Liquid Fuel Engine recent.png
LV-T30 "Reliant" Liquid Fuel Engine Small 1 100 1.25 2 000 7 50 205.16 240.0 16.74 19.58 15.789 265 310
LV-T45 LFE.png
LV-T45 "Swivel" Liquid Fuel Engine Small 1 200 1.50 2 000 7 50 167.97 215.0 11.42 14.62 13.703 250 320 3.0
KS-25 LFE.png
S3 KS-25 "Vector" Liquid Fuel Engine Small, Radial mounted 18 000 4.00 2 000 22 50 936.51 1 000.0 23.87 25.49 64.745 295 315 10.5
ToroidalAerospikeLiquidFuelEngine.png
T-1 Toroidal Aerospike "Dart" Liquid Fuel Engine Small, Radial mounted 3 850 1.00 2 000 20 50 153.53 180.0 15.66 18.35 10.797 290 340
LV-N Atomic.png
LV-N "Nerv" Atomic Rocket Motor[Note 2] Small 10 000 3.00 2 500 12 50 13.88 60.0 0.47 2.04 1.530 185 800
RE-L10.png
RE-L10 "Poodle" Liquid Fuel Engine Large 1 300 1.75 2 000 7 50 64.29 250.0 3.75 14.57 14.568 90 350 4.5
Skipper.png
RE-I5 "Skipper" Liquid Fuel Engine Large 5 300 3.00 2 000 8 50 568.75 650.0 19.33 22.09 41.426 280 320 2.0
Rockomax Mainsail transparent.png
RE-M3 "Mainsail" Liquid Engine Large 13 000 6.00 2 000 7 50 1 379.03 1 500.0 23.44 25.49 98.683 285 310 2.0
LFB KR-1x2.png
LFB KR-1x2 "Twin-Boar" Liquid Fuel Engine[Note 3] Large, Radial mounted 17 000
(14 062.4)
42.50
(10.50)
2 000 20 50 1 866.67 2 000.0 4.48
(18.13)
4.80
(19.42)
135.964 280 300 1.5
Big1.png
Kerbodyne KR-2L+ "Rhino" Liquid Fuel Engine Extra large 25 000 9.00 2 000 7 50 1 205.88 2 000.0 13.66 22.66 119.968 205 340 4.0
Quad.png
S3 KS-25x4 "Mammoth" Liquid Fuel Engine Extra large 39 000 15.00 2 000 20 50 3 746.03 4 000.0 25.47 27.19 258.978 295 315 2.0
Rapier Engine 01.png
CR-7 R.A.P.I.E.R. Engine[Note 4] Small 6 000 2.00 2 000 20 50 162.30 180.0 8.27 9.18 12.036 275 305 3.0
  1. Consumes monopropellant. (the density of monopropellant is less: 4kg/unit)
  2. Consumes liquid fuel only.
  3. The LFB KR-1x2 is a liquid fuel booster -- a combination of a "normal" engine and a fuel tank.
  4. The R.A.P.I.E.R. Engine is a combination of liquid fuel and jet engine. Only the liquid fuel engine properties are shown.
Available liquid fuel tanks
Liquid fuel and oxidizer density are both 5 kg/unit Mass
(t)
Liquid
Fuel

(Units of fuel)
Oxidizer
(Units of fuel)
Image Part Radial size Cost
(Funds)
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
R-4 FT.png
R-4 'Dumpling' External Tank Radial mounted 50
(39.90)
0.1238 0.0138 2 000 5 50 9.9 12.1
R-11 FT.png
R-11 'Baguette' External Tank Radial mounted 50
(25.21)
0.3038 0.0338 2 000 5 50 24.3 29.7
R-12 FT.png
R-12 'Doughnut' External Tank Small 147
(119.46)
0.3375 0.0375 2 000 6 50 27 33
Oscar-B FT.png
Oscar-B Fuel Tank Tiny 70
(51.64)
0.225 0.025 2 000 6 50 18 22
FL-T100 Dark.png
FL-T100 Fuel Tank Small 150
(104.1)
0.5625 0.0625 2 000 6 50 45 55
FL-T200 Dark.png
FL-T200 Fuel Tank Small 275
(183.2)
1.125 0.125 2 000 6 50 90 110
FL-T400 Dark.png
FL-T400 Fuel Tank Small 500
(316.4)
2.25 0.25 2 000 6 50 180 220
FL-T800 Dark.png
FL-T800 Fuel Tank Small 800
(432.8)
4.5 0.5 2 000 6 50 360 440
X200-8 White.png
Rockomax X200-8 Fuel Tank Large 800
(432.8)
4.5 0.5 2 000 6 50 360 440
X200-16 White.png
Rockomax X200-16 Fuel Tank Large 1 550
(815.6)
9 1 2 000 6 50 720 880
X200-32 White.png
Rockomax X200-32 Fuel Tank Large 3 000
(1 531.2)
18 2 2 000 6 50 1 440 1 760
Jumbo-64 White.png
Rockomax Jumbo-64 Fuel Tank Large 5 750
(2 812.4)
36 4 2 000 6 50 2 880 3 520
Kerbodyne S3-3600 Tank.png
Kerbodyne S3-3600 Tank Extra large 3 250
(1 597.6)
20.25 2.25 2 000 6 50 1 620 1 980
Kerbodyne S3-7200 Tank.png
Kerbodyne S3-7200 Tank Extra large 6 500
(3 195.2)
40.5 4.5 2 000 6 50 3 240 3 960
Kerbodyne S3-14400 Tank.png
Kerbodyne S3-14400 Tank Extra large 13 000
(6 390.4)
81 9 2 000 6 50 6 480 7 920
Mk2 LF+O Fuselage Short.png
Mk2 Rocket Fuel Fuselage Short Mk2 750
(566.4)
2.29 0.29 2 500 50 50 180 220
Mk2 LF+O Fuselage.png
Mk2 Rocket Fuel Fuselage Mk2 1 450
(1 082.8)
4.57 0.57 2 500 50 50 360 440
Mk3 Rocket Fuel Fuselage Short.png
Mk3 Rocket Fuel Fuselage Short Mk3 2 500
(1 352.5)
14.29 1.79 2 700 50 50 1 125 1 375
Mk3 Rocket Fuel Fuselage.png
Mk3 Rocket Fuel Fuselage Mk3 5 000
(2 705)
28.57 3.57 2 700 50 50 2 250 2 750
Mk3 Rocket Fuel Fuselage Long.png
Mk3 Rocket Fuel Fuselage Long Mk3 10 000
(5 410)
57.14 7.14 2 700 50 50 4 500 5 500
C7 Brand Adapter - 2.5m to 1.25m.png
C7 Brand Adapter - 2.5m to 1.25m Small, Large 800
(433.0)
4.57 0.57 2 300 20 50 360 440
C7 Brand Adapter Slanted - 2.5m to 1.25m.png
C7 Brand Adapter Slanted - 2.5m to 1.25m Small, Large 800
(433.0)
4.57 0.57 2 300 20 50 360 440
Mk2 to 1.25m Adapter.png
Mk2 to 1.25m Adapter Small, Mk2 550
(366.4)
2.29 0.29 2 500 50 50 180 220
Mk2 to 1.25m Adapter Long.png
Mk2 to 1.25m Adapter Long Small, Mk2 1 050
(682.8)
4.57 0.57 2 500 50 50 360 440
Mk2 Bicoupler.png
Mk2 Bicoupler Small, Mk2 x 2 860
(676.4)
2.29 0.29 2 500 50 50 180 220
2.5m to Mk2 Adapter.png
2.5m to Mk2 Adapter Large, Mk2 800
(432.8)
4.57 0.57 2 500 50 50 360 440
Mk3 to Mk2 Adapter.png
Mk3 to Mk2 Adapter Mk2, Mk3 2 200
(1 282.0)
11.43 1.43 2 600 50 50 900 1 100
Mk3 to 2.5m Adapter.png
Mk3 to 2.5m Adapter Large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
Mk3 to 2.5m Adapter Slanted.png
Mk3 to 2.5m Adapter Slanted Large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
Mk3 to 3.75m Adapter.png
Mk3 to 3.75m Adapter Extra large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
ADTP-2-3 Gray.png
Kerbodyne ADTP-2-3 Large, Extra large 1 623
(246.0)
16.88 1.88 2 000 6 50 1 350 1 650

Ion engines

A ion engine uses ionized atoms, xenon gas, and accelerate them in an electro-magnetic field and technically works different than the other rocket engines. This type of engine is very efficient but has a very low thrust making it only suitable for probes already in space.

Advantages

  • A very high specific impulse.
  • The xenon gas can be moved between tanks, which means that spacecraft with ion engines and tanks are easier and more resource-efficient to refuel than vessels with solid fuel engines, which required the entire engine bay to be replaced, while xenon gas can quickly be moved between two docked vessels.
  • The fuel doesn't need to be moved as xenon gas is used evenly.
  • Modular design: fuel and other components can be stored elsewhere in the craft.
  • Throttle can be adjusted depending on thrust requirements.
  • Can be switched off and re-ignited at will.

Disadvantages

  • Very low thrust so it is impossible to lift off from the launch pad with ion engines only.
  • No thrust vectoring is available.
Available ion engines
Thrust
(kN)
TWR Isp (s) Max. Consumption
Image Part Radial size Cost
(Funds)
Mass
(t)
Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
atm vac atm vac atm vac Electricity
(⚡/s)
Xenon
(Xenon unit/s)
PB-ION.png
IX-6315 "Dawn" Electric Propulsion System Tiny 8 000 0.25 2 000 7 50 0.048 2.0 0.019 0.816 100 4 200 8.741 0.486

RCS thrusters

The RCS thrusters are allowing an craft to change the attitude, because their thrust is low allowing tiny changes in velocity. Usually it isn't used as a main engine because the specific impulse is lower than any other liquid fuel engine.

Advantages

  • The monopropellant can be moved between tanks, which means that spacecraft with RCS thrusters and tanks are easier and more resource-efficient to refuel than vessels with solid fuel engines, which required the entire engine bay to be replaced, while monopropellant can quickly be moved between two docked vessels.
  • The fuel doesn't need to be moved as monopropellant is used evenly.
  • Modular design: fuel and other components can be stored elsewhere in the craft.
  • Can be switched off and re-ignited at will.

Disadvantages

  • Very low thrust so it is impossible to lift off from the launch pad with RCS thrusters only.
  • No thrust vectoring is available.
  • The user can only switch engines on or off, while the SAS can run them on different thrust levels in between.
  • The specific impulse is, especially in atmosphere, low and comparable with solid rocket engines.
Available RCS engines
Image Part Radial size Cost
(Funds)
Mass
(t)
Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
Thrust
(kN)
Fuel
(Units of fuel/s)
Isp (s) (atm) Isp (s) (vac)
RV-105.png
RV-105 RCS Thruster Block Radial mounted 45 0.04 1 500 15 50 1.0 0.11 100 240
Linear RCS.png
Place-Anywhere 7 Linear RCS Port Radial mounted 25 0.02 2 600 15 50 2.0 0.21 100 240
Vernor.png
Vernor Engine[Note 1] Radial mounted 150 0.08 2 000 15 50 12.0 0.94 140 260
  1. The Vernor Engine uses a liquid fuel/oxidizer mixture.

See also