Difference between revisions of "Reaction engine"

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[[Image:LV-T30 Liquid Fuel Engine.jpg|right|thumb|[[LV-T30 Liquid Fuel Engine before {{Version 0.18}}]]]]
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[[File:LV-T30 Liquid Fuel Engine recent.png|right|thumb|200px|[[LV-T30 Liquid Fuel Engine]]]]
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A '''reaction engine''' is an [[engine]] that works via “equal and opposite reaction” as in [[w:Newton%27s_laws_of_motion#Newton.27s_third_law|Newton's third law of motion]]. Specifically, they generate thrust by expelling reaction mass in the opposite direction as their acceleration. In [[Kerbal Space Program]], the reaction mass propelled outward is always a form of [[fuel]], though not always one modeled on chemical reactions.
  
−
A '''reaction engine''' is an [[engine]] that uses nothing but its onboard propellant to generate thrust. Unlike traditional air breathing [[jet engine]]s, rocket engines are able to function where no [[oxygen]] is present. If there is also a combustion it is called a '''rocket engine'''.
+
== Types ==
 +
Different sources classify kinds of reaction engine a bit differently, but all contradistinguish those which must collect outside material from those using only onboard material as reaction mass.  
  
−
== Physics ==
+
Staying relevant to KSP, we separate out [[intake air|air]]-breathing '''jet engines''' which can only operate inside an [[oxygen]]-rich [[atmosphere]] from those able to operate in space. All{{check version||1.12.3}} use the same [[resources]] and are controlled the same way.
−
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.
+
All{{check version||1.12.3}} KSP's other reaction engines can operate using only resources stored or generated onboard and are collectively called '''rocket engines'''. There are many types of rocket engines. They differ by the kind of fuel they use and the controls used to operate them in-game.  
  
−
== Solid fuel rocket engines ==
+
Listed below are general descriptions of jet engines and several broad types of rocket engines along with their advantages and disadvantages.
−
{{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 ===
+
=== Jet engines ===
 +
----
 +
{{main article|Jet engine}}
 +
{| class="wikitable floatright"
 +
|-
 +
! Advantages !! Disadvantages
 +
|-
 +
| Excellent fuel efficiency || Efficiency changes with altitude
 +
|-
 +
| Excellent thrust-to-weight ratio || Thrust output changes with speed
 +
|-
 +
| Some engines provide thrust vectoring || Does not respond rapidly to throttle changes due to turbo lag
 +
|-
 +
| || Can only be used with an oxygenated atmosphere
 +
|-
 +
| || Engines available only in 0.625m, 1.25m, and 2.5m
 +
|}
  
−
* Have a very high thrust to weight ratio.
+
Jet engines use the same fuel as rocket engines, but unlike them jets draw oxygen from the atmosphere using [[air intake]]s rather than carrying the weight of oxidizer onboard. This is represented in-game by a much lower rate of fuel consumption. The classical rocket equation doesn't hold valid for them. In flight they face the trade-off between the lower atmosphere where [[intake air]] is easily available at lower speeds but air resistance is greater, and the upper atmosphere where there's less air resistance but higher speeds are required to collect sufficient intake air.
−
* 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 ===
+
{{FlipBox
 +
|title=Available jet engines
 +
|content={{Stats Table Jet Engines}}
 +
}}
 +
{{FlipBox
 +
|title=Available jet fuel tanks
 +
|content={{Stats Table Fuselage}}
 +
}}
  
−
* Monolithic design, must be built in one piece.
+
=== Solid fuel rocket engines ===
−
* Cannot be throttled or switched off after ignition.
+
----
−
* Once spent, they are unable to use fuel from another source of the craft.
+
{{Main article|Solid rocket booster}}
 +
 
 +
{| class="wikitable floatright"
 +
|-
 +
! Advantages !! Disadvantages
 +
|-
 +
| High [[thrust-to-weight ratio]], especially in atmosphere || Cannot be throttled or switched off after ignition
 +
|-
 +
| Engine and fuel tank are a single unit || Cannot refuel or transfer fuel stored elsewhere on the craft
 +
|-
 +
| Cheap || Low efficiency compared to other types of engines
 +
|-
 +
| || No thrust vectoring
 +
|}
 +
 
 +
The most basic type of rocket engine is the [[solid fuel]] rocket. Solid fuel is simply a self-oxidizing compound or mixture within a casing with a nozzle at the end to direct the exhaust gases produced. It offers no real control beyond choosing when to ignite it, though [[tweakables]] enable altering the thrust limit and total fuel.
  
 
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}}
 
}}
  
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== Liquid fuel rocket engines ==
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=== 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 [[w:Bell nozzle|Bell nozzles]] except the only [[w:Aerospike engine|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.
+
{| class="wikitable floatright"
−
* Modular design: fuel and other components can be stored elsewhere in the craft.
+
|-
−
* Throttle can be adjusted depending on thrust requirements.
+
! Advantages !! Disadvantages
−
* Can be switched off and re-ignited at will.
+
|-
−
* Many nozzles can be gimballed for thrust vectoring.
+
| Work both in vacuum and in atmosphere || Less efficient in atmosphere than jet engines, and less efficient in space than ion engines
−
* 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.
+
|-
 +
| Can be throttled to allow fine tuning of thrust || Lower [[thrust-to-weight ratio]] compared to solid rocket engines
 +
|-
 +
| Fuel and oxidizer can be moved between tanks or vessels || Separation of engine and fuel leads to increased part count |
 +
|-
 +
| Available in a wide range of shapes, sizes, and power levels || |
 +
|-
 +
| Frequently [[gimbals|gimballed]] to allow flight control || |
 +
|-  
 +
| Immediate throttle response || |
 +
|}
  
−
=== Disadvantages ===
+
Most liquid fuel engines utilize a mixture of [[liquid fuel]] and liquid [[oxidizer]] in a 9:11 ratio — generally called “rocket fuel”. The exceptions{{check version||1.0.4}} are the [[O-10 MonoPropellant Engine]] which uses [[monopropellant]] and the [[LV-N "Nerv" Atomic Rocket Motor]] which only consumes liquid fuel (heating it in the core of a nuclear reactor rather than combusting it with oxidizer). The [[IX-6315 "Dawn" Electric Propulsion System]] uses [[xenon gas]] and [[electric charge]] to power it. This engine has a very low thrust, but is very efficient, with an [[Isp]] of over 1000 seconds. In the real world, typical liquid fuels are liquid hydrogen and a highly-refined kerosene blend called RP-1, and typical oxidizers are liquid oxygen and nitrous oxide.
  
−
* Lower power to weight ratio compared to solid rocket engines.
+
All liquid fuel rocket engines can be staged and respond to [[throttle]] controls. All engines use [[w:Bell nozzle|Bell nozzles]] except the [[Toroidal Aerospike Rocket]].
−
* Complex design with fuel tanks and other additional components.
 
−
* More points of possible failure such as if the parts tear apart from stress.
 
  
 
{{FlipBox
 
{{FlipBox
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}}
 
}}
  
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== Ion engines ==
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=== RCS thrusters ===
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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.
+
 
 +
{| class="wikitable floatright"
 +
|-
 +
! Advantages !! Disadvantages
 +
|-
 +
| [[Monopropellant]] is automatically routed || No throttle; either switched on or off
 +
|-
 +
| Offers rotation and translation maneuverability || Low thrust and low thrust-to-weight ratio
 +
|-
 +
| Offers additional thrust for SAS when reaction wheels cannot provide enough torque || Low fuel efficiency
 +
|}
  
−
=== Advantages ===
+
RCS thrusters make up the [[Reaction Control System]] designed primarily for translation maneuvers, especially useful during [[docking]]. They cannot be [[throttle]]d and are controlled with a separate set of keys from the pitch-yaw-roll keys. They use only [[monopropellant]] fuel, except for the [[Vernor Engine]] which uses rocket fuel.  Monopropellant flows automatically from tanks mounted anywhere on a vessel to thrusters mounted anywhere on a vessel, so there is no need to set up fuel lines or mount thrusters directly on tanks if it is inconvenient or unsightly.
−
* 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.
+
In addition to separate thruster parts, the [[Mk1-3 Command Pod]] has its own built-in RCS thrusters, with the same power and I<sub>sp</sub> profile as the RC-105 RCS Thruster Block.
−
* 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.
 
  
 
{{FlipBox
 
{{FlipBox
−
|title=Available ion engines
+
|title=Available RCS engines
−
|content={{Stats Table Xenon Engines}}
+
|content={{Stats Table RCS Thrusters}}
 +
}}
 +
{{FlipBox
 +
|title=Available monopropellant tanks
 +
|content={{Stats Table RCS Fuel}}
 
}}
 
}}
  
−
== RCS thrusters ==
+
=== Ion engines ===
−
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.
+
 
 +
{| class="wikitable floatright"
 +
|-
 +
! Advantages !! Disadvantages
 +
|-
 +
| Extremely high efficiency || Extremely low thrust; inefficient for orbital transfers
 +
|-
 +
| Cool blue glow || Uncool excessive electric consumption
 +
|-
 +
| || No engine gimbal
 +
|-
 +
| || Xenon containers have lower mass ratio than rocket fuel tanks
 +
|}
  
−
=== Advantages ===
+
An ion engine uses [[electric charge]] to ionize atoms of [[xenon gas]] and accelerate them in an electrostatic or electromagnetic field to propel them as exhaust. Remarkably little xenon gas is needed, and probes equipped with just a few tanks are considered able to operate forever, or until something inevitably goes wrong. However, ion engines are very demanding on electrical generation and storage and very slow to accelerate.
−
* 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 ===
+
In real-life, they are often not considered true “rocket” engines. But given that they require no outside material or mass to operate, for ease and simplicity they are included with rocket engines on this wiki.
−
* 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.
 
  
 +
{{Wikipedia|Hall effect thruster}}
 +
{{FlipBox
 +
|title=Available ion engines
 +
|content={{Stats Table Xenon Engines}}
 +
}}
 
{{FlipBox
 
{{FlipBox
−
|title=Available RCS engines
+
|title=Available xenon tanks
−
|content={{Stats Table RCS Thrusters}}
+
|content={{Stats Table Xenon Tanks}}
 
}}
 
}}
  
 
== See also ==
 
== See also ==
 
* {{Wikipedia|Reaction engine}}
 
* {{Wikipedia|Reaction engine}}
 +
* {{Wikipedia|Jet engine}}
 
* {{Wikipedia|Rocket engine}}
 
* {{Wikipedia|Rocket engine}}
  
 
[[Category:Engines]]
 
[[Category:Engines]]

Latest revision as of 10:46, 30 November 2022

LV-T30 Liquid Fuel Engine

A reaction engine is an engine that works via “equal and opposite reaction” as in Newton's third law of motion. Specifically, they generate thrust by expelling reaction mass in the opposite direction as their acceleration. In Kerbal Space Program, the reaction mass propelled outward is always a form of fuel, though not always one modeled on chemical reactions.

Types

Different sources classify kinds of reaction engine a bit differently, but all contradistinguish those which must collect outside material from those using only onboard material as reaction mass.

Staying relevant to KSP, we separate out air-breathing jet engines which can only operate inside an oxygen-rich atmosphere from those able to operate in space. All use the same resources and are controlled the same way.

All KSP's other reaction engines can operate using only resources stored or generated onboard and are collectively called rocket engines. There are many types of rocket engines. They differ by the kind of fuel they use and the controls used to operate them in-game.

Listed below are general descriptions of jet engines and several broad types of rocket engines along with their advantages and disadvantages.

Jet engines

→ Main article: Jet engine
Advantages Disadvantages
Excellent fuel efficiency Efficiency changes with altitude
Excellent thrust-to-weight ratio Thrust output changes with speed
Some engines provide thrust vectoring Does not respond rapidly to throttle changes due to turbo lag
Can only be used with an oxygenated atmosphere
Engines available only in 0.625m, 1.25m, and 2.5m

Jet engines use the same fuel as rocket engines, but unlike them jets draw oxygen from the atmosphere using air intakes rather than carrying the weight of oxidizer onboard. This is represented in-game by a much lower rate of fuel consumption. The classical rocket equation doesn't hold valid for them. In flight they face the trade-off between the lower atmosphere where intake air is easily available at lower speeds but air resistance is greater, and the upper atmosphere where there's less air resistance but higher speeds are required to collect sufficient intake air.

Available jet engines
Image Part Radial size Cost
(Funds)		 Mass
(t)		 Max. Temp.
(K)		 Tolerance
(m/s)		 Tolerance
(g) 		Thrust
(kN) 		TWR Fuel
(Units of fuel/s) 		Intake
(Air unit/s) 		Isp (s) TVC
(°) 		Reverse
J90JunoBasicJetEngine.png
 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
J33WheesleyBasicJetEngine.png
 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
J404PantherAfterburningTurbofan.png
 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 /
0.663 		7.705 /
7.954 		9 000 /
4 000 		10.0 No
JX4WhiplashTurboRamjetEngine.png
 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.
Available jet fuel tanks
Liquid Fuel Density is 5 kg/unit Mass
(t) 		Liquid
Fuel
(Units of fuel)
Image Part Radial size Cost
(Funds)		 Full Empty Max. Temp.
(K)		 Tolerance
(m/s)		 Tolerance
(g)
Engine Nacelle.png
 Engine Nacelle[Note 1] Small 600
(480) 		0.925 0.15 2 000 10 50 150
Engine Pre-cooler.png
 Engine Pre-cooler[Note 1] Small 1 650
(1 618) 		0.375 0.15 2 000 10 50 40
Mk1 Fuselage-Intake.png
 Mk1 Diverterless Supersonic Intake[Note 1] Small 720
(560) 		1.18 0.17 2 000 10 50 200
Mk0LiquidFuelFuselage.png
 Mk0 Liquid Fuel Fuselage Tiny 200
(160) 		0.275 0.025 2 000 10 50 50
Mk1 Liquid Fuel Fuselage.png
 Mk1 Liquid Fuel Fuselage Small 550
(230) 		2.25 0.25 2 000 10 50 400
Mk2 Liquid Fuselage Short.png
 Mk2 Liquid Fuel Fuselage Short Mk2 750
(430) 		2.29 0.29 2 500 50 50 400
Mk2 FT.png
 Mk2 Liquid Fuel Fuselage Mk2 1 450
(810) 		4.57 0.57 2 500 50 50 800
Mk3 Liquid Fuel Fuselage Short.png
 Mk3 Liquid Fuel Fuselage Short Mk3 4 300
(2 300) 		14.29 1.79 2 700 50 50 2 500
Mk3 Liquid Fuel Fuselage.png
 Mk3 Liquid Fuel Fuselage Mk3 8 600
(4 600) 		28.57 3.57 2 700 50 50 5 000
Mk3 Liquid Fuel Fuselage Long.png
 Mk3 Liquid Fuel Fuselage Long Mk3 17 200
(9 200) 		57.14 7.14 2 700 50 50 10 000
NCS Adapter.png
 NCS Adapter Small, Tiny 320
(256) 		0.5 0.1 2 400 10 50 80
FAT455AirplaneWing.png
 FAT-455 Aeroplane Main Wing[Note 2] X 2 800
(2 320) 		3.78 0.78 1 200 15 50 600
BigSWingStrake.png
 Big-S Wing Strake[Note 2] X 1 000
(920) 		0.6 0.1 2 400 15 50 100
BigSDeltaWing.png
 Big-S Delta Wing[Note 2] X 3 000
(2 760) 		2.0 0.5 2 400 15 50 300
  1. ↑ 1.0 1.1 1.2 The Engine Nacelle, Engine Pre-cooler, and Mk1 Diverterless Supersonic Intake are a combination of air intake and liquid fuel tank. Only the tank properties are shown. They are located in the "Aerodynamic" category in the game.
  2. ↑ 2.0 2.1 2.2 The FAT-455 Aeroplane Main Wing, Big-S Wing Strake, and Big-S Delta Wing are a combination of lifting surface and liquid fuel tank. Only the tank properties are shown. They are located in the "Aerodynamic" category in the game.

Solid fuel rocket engines

→ Main article: Solid rocket booster
Advantages Disadvantages
High thrust-to-weight ratio, especially in atmosphere Cannot be throttled or switched off after ignition
Engine and fuel tank are a single unit Cannot refuel or transfer fuel stored elsewhere on the craft
Cheap Low efficiency compared to other types of engines
No thrust vectoring

The most basic type of rocket engine is the solid fuel rocket. Solid fuel is simply a self-oxidizing compound or mixture within a casing with a nozzle at the end to direct the exhaust gases produced. It offers no real control beyond choosing when to ignite it, though tweakables enable altering the thrust limit and total fuel.

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 Disadvantages
Work both in vacuum and in atmosphere Less efficient in atmosphere than jet engines, and less efficient in space than ion engines
Can be throttled to allow fine tuning of thrust Lower thrust-to-weight ratio compared to solid rocket engines
Fuel and oxidizer can be moved between tanks or vessels
Available in a wide range of shapes, sizes, and power levels
Frequently gimballed to allow flight control
Immediate throttle response

Most liquid fuel engines utilize a mixture of liquid fuel and liquid oxidizer in a 9:11 ratio — generally called “rocket fuel”. The exceptions[outdated] are the O-10 MonoPropellant Engine which uses monopropellant and the LV-N "Nerv" Atomic Rocket Motor which only consumes liquid fuel (heating it in the core of a nuclear reactor rather than combusting it with oxidizer). The IX-6315 "Dawn" Electric Propulsion System uses xenon gas and electric charge to power it. This engine has a very low thrust, but is very efficient, with an Isp of over 1000 seconds. In the real world, typical liquid fuels are liquid hydrogen and a highly-refined kerosene blend called RP-1, and typical oxidizers are liquid oxygen and nitrous oxide.

All liquid fuel rocket engines can be staged and respond to throttle controls. All engines use Bell nozzles except the Toroidal Aerospike Rocket.

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.
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 X 50
(39.90) 		0.1238 0.0138 2 000 5 50 9.9 12.1
R-11 FT.png
 R-11 'Baguette' External Tank X 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

RCS thrusters

Advantages Disadvantages
Monopropellant is automatically routed No throttle; either switched on or off
Offers rotation and translation maneuverability Low thrust and low thrust-to-weight ratio
Offers additional thrust for SAS when reaction wheels cannot provide enough torque Low fuel efficiency

RCS thrusters make up the Reaction Control System designed primarily for translation maneuvers, especially useful during docking. They cannot be throttled and are controlled with a separate set of keys from the pitch-yaw-roll keys. They use only monopropellant fuel, except for the Vernor Engine which uses rocket fuel. Monopropellant flows automatically from tanks mounted anywhere on a vessel to thrusters mounted anywhere on a vessel, so there is no need to set up fuel lines or mount thrusters directly on tanks if it is inconvenient or unsightly.

In addition to separate thruster parts, the Mk1-3 Command Pod has its own built-in RCS thrusters, with the same power and Isp profile as the RC-105 RCS Thruster Block.

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-1X.png
 RV-1X Variable Thruster Block Radial mounted 30 0.005 1 500 12 50 0.1 0.01 100 240
PlaceAnywhere1.png
 Place Anywhere 1 Linear RCS Port Radial mounted 15 0.001 1 500 12 50 0.2 0.02 100 240
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.
Available monopropellant tanks
RCS Fuel Density is 4 kg/unit Mass
(t) 		Monopropellant
(Units of fuel)
Image Part Radial size Cost
(Funds)		 Full Empty Max. Temp.
(K)		 Tolerance
(m/s)		 Tolerance
(g)
FL-R10.png
 FL-R20 RCS Fuel Tank Tiny 200
(176) 		0.10 0.02 2 000 12 50 20
FL-R25 FT.png
 FL-R120 RCS Fuel Tank Small 330
(186) 		0.56 0.08 2 000 12 50 120
FL-R1 Yellow.png
 FL-R750 RCS Fuel Tank Large 1 800
(900) 		3.4 0.4 2 000 12 50 750
Mk2 Monopropellant Tank.png
 Mk2 Monopropellant Tank Mk2 750
(270) 		1.89 0.29 2 500 50 50 400
Mk3 Monopropellant Tank.png
 Mk3 Monopropellant Tank Mk3 5 040
(2 520) 		9.8 1.4 2 700 50 50 2 100
Stratus-v roundified monopropellant tank.png
 Stratus-V Roundified Monopropellant Tank X 200
(176) 		0.10 0.02 2 000 12 50 20
Stratus-V Cylindrified.png
 Stratus-V Cylindrified Monopropellant Tank X 250
(190) 		0.23 0.03 2 000 12 50 50

Ion engines

Advantages Disadvantages
Extremely high efficiency Extremely low thrust; inefficient for orbital transfers
Cool blue glow Uncool excessive electric consumption
No engine gimbal
Xenon containers have lower mass ratio than rocket fuel tanks

An ion engine uses electric charge to ionize atoms of xenon gas and accelerate them in an electrostatic or electromagnetic field to propel them as exhaust. Remarkably little xenon gas is needed, and probes equipped with just a few tanks are considered able to operate forever, or until something inevitably goes wrong. However, ion engines are very demanding on electrical generation and storage and very slow to accelerate.

In real-life, they are often not considered true “rocket” engines. But given that they require no outside material or mass to operate, for ease and simplicity they are included with rocket engines on this wiki.

Hall effect thruster on Wikipedia

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
Available xenon tanks
Xenon density is 0.1 kg/unit Mass
(t) 		Xenon
(Xenon unit)
Image Part Radial size Cost
(Funds)		 Full Empty Max. Temp.
(K)		 Tolerance
(m/s)		 Tolerance
(g)
PB-X50R.png
 PB-X50R Xenon Container Radial mounted 2 220
(600) 		0.054 0.014 2 000 12 50 405
Pb-x150 xenon container.png
 PB-X150 Xenon Container Tiny 3 680
(800) 		0.100 0.024 2 000 6 50 720
PB-X750 Xenon Container.png
 PB-X750 Xenon Container Small 24 300
(1 500) 		0.76 0.19 2 000 6 50 5 700

See also

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