Difference between revisions of "Reaction engine"
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− | [[File:LV-T30 Liquid Fuel Engine. | + | [[File:LV-T30 Liquid Fuel Engine recent.png|right|thumb|200px|[[LV-T30 Liquid Fuel Engine]]]] |
− | A '''reaction engine''' is an [[engine]] that works via “equal and opposite | + | 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. |
== Types == | == 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. | 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 [[intake air|air]]-breathing '''jet engines''' which can only operate inside an [[oxygen]]-rich [[atmosphere]]. All{{check version|| | + | 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{{check version|| | + | 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. |
Listed below are general descriptions of jet engines and several broad types of rocket engines along with their advantages and disadvantages. | Listed below are general descriptions of jet engines and several broad types of rocket engines along with their advantages and disadvantages. | ||
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{{main article|Jet engine}} | {{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 | ||
+ | |} | ||
+ | |||
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. | 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. | ||
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− | |title=Available | + | |title=Available jet fuel tanks |
|content={{Stats Table Fuselage}} | |content={{Stats Table Fuselage}} | ||
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{{Main article|Solid rocket booster}} | {{Main article|Solid rocket booster}} | ||
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− | = | + | {| 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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=== Liquid fuel rocket engines === | === Liquid fuel rocket engines === | ||
− | |||
− | |||
− | + | {| class="wikitable floatright" | |
+ | |- | ||
+ | ! 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 || 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 || | | ||
+ | |} | ||
− | The [[LV-N Atomic Rocket Motor]] | + | 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. |
− | + | 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]]. | |
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=== RCS thrusters === | === RCS thrusters === | ||
− | |||
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− | = | + | {| 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 | ||
+ | |} | ||
+ | |||
+ | 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. | ||
− | + | 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. | |
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=== Ion engines === | === Ion engines === | ||
− | ---- | + | |
+ | {| 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 | ||
+ | |} | ||
+ | |||
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. | 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. | 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. | ||
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{{Wikipedia|Hall effect thruster}} | {{Wikipedia|Hall effect thruster}} |
Latest revision as of 10:46, 30 November 2022
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.
Contents
[hide]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.
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.
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.
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.
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
See also
- Reaction engine on Wikipedia
- Jet engine on Wikipedia
- Rocket engine on Wikipedia