Reaction engine

LV-T30 Liquid Fuel Engine

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 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 ()	Thrust (kN)		TWR				Isp (s)		Burn (s)
												Full		Empty
Image	Part	Radial size	Cost ()	Full	Empty	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)		atm	vac	atm	vac	atm	vac	atm	vac
	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 "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 "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
	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 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
	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 it's 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 (/s)	Isp (s)		TVC
Image	Part	Radial size	Cost ()	Mass (t)	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)	atm	vac	atm	vac		atm	vac	Gimbal (°)
	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 "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 "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 "Puff" MonoPropellant Fuel Engine	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 "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 "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 "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 "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 "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
	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
	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 "Nerv" Atomic Rocket Motor	Small	10 000	3.00	2 500	12	50	13.88	60.0	0.47	2.04	1.530	185	800	—
	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
	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
	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 "Twin-Boar" Liquid Fuel Engine	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
	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
	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
	CR-7 R.A.P.I.E.R. Engine	Small	6 000	2.00	2 000	20	50	162.30	180.0	8.27	9.18	12.036	275	305	3.0

Available liquid fuel tanks

Liquid fuel and oxidizer density are both 5 kg/unit				Mass (t)					Liquid Fuel ()	Oxidizer ()
Image	Part	Radial size	Cost ()	Full	Empty	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)
	R-4 'Dumpling' External Tank	X	50 (39.90)	0.1238	0.0138	2 000	5	50	9.9	12.1
	R-11 'Baguette' External Tank	X	50 (25.21)	0.3038	0.0338	2 000	5	50	24.3	29.7
	R-12 'Doughnut' External Tank	Small	147 (119.46)	0.3375	0.0375	2 000	6	50	27	33
	Oscar-B Fuel Tank	Tiny	70 (51.64)	0.225	0.025	2 000	6	50	18	22
	FL-T100 Fuel Tank	Small	150 (104.1)	0.5625	0.0625	2 000	6	50	45	55
	FL-T200 Fuel Tank	Small	275 (183.2)	1.125	0.125	2 000	6	50	90	110
	FL-T400 Fuel Tank	Small	500 (316.4)	2.25	0.25	2 000	6	50	180	220
	FL-T800 Fuel Tank	Small	800 (432.8)	4.5	0.5	2 000	6	50	360	440
	Rockomax X200-8 Fuel Tank	Large	800 (432.8)	4.5	0.5	2 000	6	50	360	440
	Rockomax X200-16 Fuel Tank	Large	1 550 (815.6)	9	1	2 000	6	50	720	880
	Rockomax X200-32 Fuel Tank	Large	3 000 (1 531.2)	18	2	2 000	6	50	1 440	1 760
	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	Extra large	3 250 (1 597.6)	20.25	2.25	2 000	6	50	1 620	1 980
	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	Extra large	13 000 (6 390.4)	81	9	2 000	6	50	6 480	7 920
	Mk2 Rocket Fuel Fuselage Short	Mk2	750 (566.4)	2.29	0.29	2 500	50	50	180	220
	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	Mk3	2 500 (1 352.5)	14.29	1.79	2 700	50	50	1 125	1 375
	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	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	Small, Large	800 (433.0)	4.57	0.57	2 300	20	50	360	440
	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	Small, Mk2	550 (366.4)	2.29	0.29	2 500	50	50	180	220
	Mk2 to 1.25m Adapter Long	Small, Mk2	1 050 (682.8)	4.57	0.57	2 500	50	50	360	440
	Mk2 Bicoupler	Small, Mk2 x 2	860 (676.4)	2.29	0.29	2 500	50	50	180	220
	2.5m to Mk2 Adapter	Large, Mk2	800 (432.8)	4.57	0.57	2 500	50	50	360	440
	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	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	Large, Mk3	2 500 (1 353.0)	14.29	1.79	2 600	50	50	1 125	1 375
	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
	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 ()	Mass (t)	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)	atm	vac	atm	vac	atm	vac	Electricity (⚡/s)	Xenon (/s)
	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 ()	Mass (t)	Max. Temp. (K)	Tolerance (m/s)	Tolerance (g)	Thrust (kN)	Fuel (/s)	Isp (s) (atm)	Isp (s) (vac)
	RV-1X Variable Thruster Block	Radial mounted	30	0.005	1 500	12	50	0.1	0.01	100	240
	Place Anywhere 1 Linear RCS Port	Radial mounted	15	0.001	1 500	12	50	0.2	0.02	100	240
	RV-105 RCS Thruster Block	Radial mounted	45	0.04	1 500	15	50	1.0	0.11	100	240
	Place-Anywhere 7 Linear RCS Port	Radial mounted	25	0.02	2 600	15	50	2.0	0.21	100	240
	Vernor Engine	Radial mounted	150	0.08	2 000	15	50	12.0	0.94	140	260

Direct Comparison

All engines have specific properties that make them more or less suited for a specific purpose. This list should help you decide which engine is right for you.

engine name	Tech tree level	Fuel	Thrust Vectoring	Attachment/Size
LV-T30 Liquid Fuel Engine	1	Liquid	-	Small
LV-T45 Liquid Fuel Engine	3	Liquid	1.0°	Small
LV-909_Liquid_Fuel_Engine	3	Liquid	0.5°	Small
Rockomax Mark 55 Radial Mount Liquid Engine	4	Liquid	3.0°	Radial
Rockomax "Poodle" Liquid Engine	5	Liquid	2.5°	Large
RT-10 Solid Fuel Booster	1	Solid	-	Small
Rockomax BACC Solid Fuel Booster	3	Solid	-	Small
Sepratron I	3	Solid	-	Radial

See also

• Reaction engine on Wikipedia
• Rocket engine on Wikipedia