Reaction engine

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A rocket engine is an engine that uses nothing but its onboard propellant to generate thrust. Unlike traditional air breathing engines used by atmospheric crafts rocket engines are able to function in a vacuum where no oxygen is present.

History

Rocket engines were present in KSP in all public releases of the game.

Approaches to rocket engines

Rocket engines come in two commonly used forms. The first and 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. There are currently two booster rocket sizes included.

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.

Solid fuel rocket engines

→ Main article: Solid rocket booster

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 ammounts 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)
0.0725 0.0125 2 000 7 50 8 13.79 18.0 19.40 25.32 112.51 146.84 118 154 5.0
Mite.png
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
Shrimp.png
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
Thorougbred.png
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
Clydesdale.png
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

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
SkipperV2.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
MainsailV2.png
RE-M3 "Mainsail" Liquid Fuel 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.