Different Engines in KSP

[WillThe84th]

If you are new to KSP or to Rocket Science in general, you might not know what all the different engines that the game offers do, or how they work, or why you would use one instead of the other. At it's most basic level, the engines in the game take some sort of fuel, and accelerate it out the back of the rocket/plane and, because of Newton's Third Law, this propels the craft forward. How the engine does this depends on the type of engine, and in KSP, at this time, there are five different types of engines. These are: Chemical Rockets, Jet Engines, Solid Rocket Boosters, Ion Thrusters, and Nuclear Thermal Rockets. (There is only one Ion Thruster and only one Nuclear Thermal Rocket)

Quick Note: All engines have different characteristics, thrust, ISP a sea level, and ISP in vacuum. Thrust is how much force the engine exerts, and ISP measures how efficient the engine is, so an engine with an ISP of 400 will use half as much fuel to produce the same thrust as an engine with an ISP of 200.

Chemical Rockets:

Thrust: 2-4000, ISP ASL: 80-295, ISP Vacuum: 290-350 (Not including "Puff" Monopropellant Engine)

     

Chemical Rockets (or Liquid Fuel Engines) require Liquid Fuel and Oxidizer, and is one of the most common engines that you will use in the game. The basic concept is that the fuel is burned inside a combustion chamber and then the heated exhaust expands through the nozzle and is shot out the back. These engines are somewhat efficient, and have pretty high thrust. There is a very large variety of these engines so each one is fit for a particular job. For instance there are some of them that are more efficient in the atmosphere than others and some might be very efficient in space. You're sure to find one that fits your needs.

Jet Engines:

Thrust (Mach 0): 20-360, ISP ASL: 3200-12600

                        

Jet Engines only require Liquid Fuel, but they also need Intakes.  These engines work by taking air from the atmosphere, compressing it, mixing it with the fuel and then burning it in the combustion chamber. They exhaust then shoots out the back, propelling the craft forward. They also only work in atmospheres with oxygen, (Kerbin and Laythe) and if they are deprived of air, (if you go too high) the engines will flame out and stop producing thrust. Like the Chemical Rockets there a different types of Jet Engines in the game. There are high efficiency, low thrust engines, and there are low efficiency, high thrust ones too.

Solid Rocket Boosters:

Thrust: 18-750, ISP ASL: 118-195, ISP Vacuum: 154-220

                              

Solid Rocket Boosters (or SRBs for short) only need one fuel called Solid Fuel, which they carry themselves. These engines differ from other ones because, unlike the Jet Engines and the Chemical Rockets, all of their fuel is stored inside the combustion chamber. This means that when you start these engines (with an ignition charge at the top of the booster) they will continue to run until all their fuel is used up, so you can't shut them off. Solid Rocket Boosters are low efficiency, high thrust engines, and are best used during ascent.

Ion Thrusters:

Thrust: 2, ISP ASL: 100, ISP Vacuum: 4200

Ion Thrusters need a resource called Xenon Gas (pronounced Zee-non) and also require Electric Charge. These engines are very complicated, but basically they use electricity to ionize (charge by adding or removing an electron) particles and then shoot them out of the back at insanely high velocities. These engine are incredibly efficient in space (12 times more than the most efficient Chemical Rocket) but they produce practically no thrust. Because of their low thrust, they are best used on small crafts like probes.

Nuclear Thermal Rockets:

Thrust: 60, ISP ASL: 185, ISP Vacuum: 800

      

Nuclear Thermal Rockets only need Liquid Fuel. The concept of these engines is my favorite. They work by heating up the fuel with a small Nuclear Reactor and then shooting the fuel out the back. The Nuclear Reactor allows the fuel to get hotter than it does in a Chemical Rocket, which means that the fuel is more energetic, which then leads to it going faster out the nozzle of the engine, which means that the engine is more efficient. This engine is about two times more efficient than the most efficient Chemical Rocket, but the Nuclear Reactor can cause the engine to overheat, (so radiators are almost always required) and it doesn't produce much thrust.

R.A.P.I.E.R Engine:

Jet Engine: Thrust (Mach 0): 105, ISP ASL: 3200

Chemical Rocket: Thrust: 180, ISP ASL: 275, ISP Vacuum: 305

There is an engine in the game called the R.A.P.I.E.R, and that engine has two modes, Airbreathing (Jet Engine) and Closed Cycle. (Chemical Rocket) It is mainly used for a type of spaceplane called an SSTO. (Single Stage to Orbit)

P.S: I got all the images from the KSP Wiki.

P.P.S: If I missed anything or did something wrong, please tell me. Also, if you want more of this sort of stuff, say so.

Edited January 10, 2016 by WillThe84th

[problemecium]

This is good. With some expansions (e.g. a proper blurb about the RAPIER and perhaps something about Isp) and revisions it would make a good wiki article.

In the interest of helping, here's some corrections I've spotted that need to be made:
- Jet Engines: "flameout" in this context should be "flame out" ("flameout" is a noun while "flame out" is a verb. Blame the language)
- Jet Engines: You mentioned low thrust and high efficiency, and then low thrust and low efficiency. Did you mean high thrust and low efficiency?
- SRBs: "all of there fuel is stored inside" should be "all of their fuel is stored inside"
- SRBS: "best used during assent" should be "best used during ascent"

[WillThe84th]

26 minutes ago, parameciumkid said:

This is good. With some expansions (e.g. a proper blurb about the RAPIER and perhaps something about Isp) and revisions it would make a good wiki article.

In the interest of helping, here's some corrections I've spotted that need to be made:
- Jet Engines: "flameout" in this context should be "flame out" ("flameout" is a noun while "flame out" is a verb. Blame the language)
- Jet Engines: You mentioned low thrust and high efficiency, and then low thrust and low efficiency. Did you mean high thrust and low efficiency?
- SRBs: "all of there fuel is stored inside" should be "all of their fuel is stored inside"
- SRBS: "best used during assent" should be "best used during ascent"

Thank you.

[problemecium]

Oh, and I forgot to mention the thread title says "Different Engines is KSP" when presumably you meant "in KSP"

[WillThe84th]

Yeah, I make a lot of typos...

[RokRoland]

I think the post is a good introduction, but for the newbie and in order to understand rocketry, more glossing over the concepts of "Thrust" and specifically "ISP" in a more structured way would be a great benefit.

In elaboration, "how fast fuel comes out the back" does absolutely nothing to describe the concept of ISP. However the next sentence does, but you could include an example which states that an engine with an ISP of 400 uses only half the fuel to produce the same thrust as an engine with the ISP of 200. Additionally you do mention ISP in atmosphere and ISP in vacuum but what these mean in practice are not elaborated on. And, even though thrust is a basic concept, dismissing it as "self-explanatory" may not be the most helpful way to approach a tutorial.

I think that by adding more information on these topics would truly help the newbie to understand how to choose rocket engines.

[sal_vager]

Nice thread @WillThe84th, stickied for January 2016!

[SchweinAero]

On 8.12.2015 at 11:28 PM, WillThe84th said:

 

 

 

 

[the Rapier] is mainly used for a type of spaceplane called an SSTO. (Single Stage to Orbit)

Hate to be that guy, but could you correct this to avoid the confusion? SSTO is to spaceplane as car is to electric.

Edited January 26, 2016 by SchweinAero