How really rocket is ignited?

[Pawelk198604]

I am very interested in rocketry, which is why I bought KSP 3 years ago :-)

I wonder at what point and how the ignition of the rocket, I mean, of course, for liquid fuel rockets, although the solid fuel also interests me.

When I am lighting my gas stove, I use a spark generators mounted at the burner or manual the sparker when those at the burner does not work :-)

I liked to watch space shuttle takeoffs for a few seconds before the start popping sparks under engines of the shuttle, I wondered whether in this way they are ignited

[Budgie]

I believe those sparks are to ignite any hydrogen that builds up inside the nozzle of the engine. If the Shuttle were to start with that extra hydrogen gas inside the bell of the nozzle, the result would be rather more explosive than expected.

Other rockets sometimes use a small piece of solid rocket fuel that is ignited with an electric match or other electricity-powered means

[Sampa]

If my knowledege of jet engines serves in the same way, they would start the ignitors before pumping fuel to the engines. You actually would not see either of these functions because it's completely internal. In a normal jet, if fuel was pumped in first, youd have a puddle of it at the bottom of the combustion chamber. When that is , ignited, you have a hot start which has more pressure than it is supposed to have. It is much the same function in a rocket engine because they both,act on the very same principles.

[RainDreamer]

Sometimes you get hypergolic fuel that just go kaboom when they are mixed together, no extra ignition needed!

[sgt_flyer]

Welllll - the best answer will be - it depends hypergolic rocket engines obviously don't need an ignition system.

(Proton rocket, the old Ariane 4 rocket)

Non hypergolic systems use various means, but the origin of the ignition is always within the combustion chamber, because rocket engines need a stable combustion (SSMEs have a sparkplug like system in the middle of the injectors http://blogs.nasa.gov/J2X/tag/ignition/ )

Other engines can use a liquid that is hypergolic with either the fuel or the oxidizer - they inject a small amount of it within the combustion chamber, reacting with either the oxidizer or the fuel, then the combustion reaction is sustained.

One example, boron based compounds (green flame at ignition ! - SpaceX falcon 9 use this stuff -saturn V F-1 engines also used it)

https://en.m.wikipedia.org/wiki/Triethylborane

There's also the possibility of using pyrotechnics to trigger the ignition (though obviously, it's generally for non restartable engines:p)

Some companies work on laser ignitors too

Soo - there's a lot of options, depending on the fuels used, the kind of work the engine will have to do (restartable / non restartable / air started / ground started)

Edited October 6, 2015 by sgt_flyer

[Laie]

To the best of my knowledge, there's basically three four methods:

• pyrotechnics. basically, a blank cartridge. Several may be carried; earlier Agena engines used that approach.
  
• a spark plug is used in the RL-10 and J-2 engines.
  
• hypergolics, which reliably ignite on contact (e.g. later Agena as used with Gemini).
  
• a small amount of hypergolics is used for ignition only.
  

[Tex_NL]

See those sparks? That's what ignited the shuttles engines.

[Red Iron Crown]

Sometimes you get hypergolic fuel that just go kaboom when they are mixed together, no extra ignition needed!

Sometimes hypergolics are used to start the ignition of non-hypergolic fuels.

[shynung]

Yep. Starter slugs, as the Late John D. Clark put it.

[Budgie]

-snip-

See those sparks? That's what ignited the shuttles engines.

See my first reply to this OP.

Also this link

http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts115/launch/qa-leinbach.html

[Sampa]

See those sparks? That's what ignited the shuttles engines.

No, they are not. Nasa has already debunked that theory. Those sparklers are only to burn up hydrogen vapors that may have otherwise leaked.

[RainDreamer]

No, they are not. Nasa has already debunked that theory. Those sparklers are only to burn up hydrogen vapors that may have otherwise leaked.

Soo...why is that a bad thing? If the engine ignite the whole place will be on fire either way right?

[Sampa]

Soo...why is that a bad thing? If the engine ignite the whole place will be on fire either way right?

Ydrogen, as a vapor is very explosive. We are talking safety. That pad is designed to handle the saturn v rocket. But, the hydrogen vapors were a bit more of a problem because the tank running the ssme was un the belly of the shuttle and not inline with the rest of the vehicle.

[zxczxczbfg]

RainDreamer said:

Soo...why is that a bad thing? If the engine ignite the whole place will be on fire either way right?

Not quite. Having extra hydrogen built up in the engine bells when the main engines ignite is what engineers call a Very Bad Thing. You're sitting on many tons of highly explosive substances; having some leaking when the rocket engines start is a disaster waiting to happen. It wouldn't matter much to the launch pad, but it might matter a lot to the spacecraft.

Edit: Ah, gorrammit. Ninja'd!

Edited December 2, 2015 by zxczxczbfg

[Endersmens]

Soo...why is that a bad thing? If the engine ignite the whole place will be on fire either way right?

It's like this. If you have a propane stove, you turn on the gas and then light it. The gas is moving out quickly, and when it's ignited, it turned into a sustained flame.

Now, fill an entire room with propane and light a match. Get it now? Gas build up causes big boom. With extra hydrogen in the bell, when the engine is started, this hydrogen will combust, putting pressure on the engine, on top of the pressure from the engine firing.

Double ninja'd but I provided an analogy.

[Sampa]

Not quite. Having extra hydrogen built up in the engine bells when the main engines ignite is what engineers call a Very Bad Thingâ„¢. You're sitting on many tons of highly explosive substances; having some leaking when the rocket engines start is a disaster waiting to happen. It wouldn't matter much to the launch pad, but it might matter a lot to the spacecraft.

Edit: Ah, gorrammit. Ninja'd!

It's alright, yours is a little more informative anyway.

[PB666]

All wrong, its lit with a 1937 mother of pearl inlaid on solid platinum cigarette lighter held by the newest guy in the 'make them go to space today rotation'. I hear the health insurance is pretty good but they dock your wages if you lose the lighter. Just look for the shiney bald headed guy with no body hair.

Should i add a smiley face, heh, nah, they will eventually figure it out.

[Sampa]

All wrong, its lit with a 1937 mother of pearl inlaid on solid platinum cigarette lighter held by the newest guy in the 'make them go to space today rotation'. I hear the health insurance is pretty good but they dock your wages if you lose the lighter. Just look for the shiney bald headed guy with no body hair.

Should i add a smiley face, heh, nah, they will eventually figure it out.

Very funny, PB

[Jovus]

All wrong, its lit with a 1937 mother of pearl inlaid on solid platinum cigarette lighter held by the newest guy in the 'make them go to space today rotation'. I hear the health insurance is pretty good but they dock your wages if you lose the lighter. Just look for the shiney bald headed guy with no body hair.

Small correction: while the original plans call for the use of the 1937 lighter, it was lost in a testing accident. Instead, for the life of the STS program, they used a 1919 Solingen 'zippo' lighter from the Gemini program surplus locker. Unfortunately, while very good for their time, even Solingen's lighters were somewhat unreliable, which was the #1 cause of scrubbed launches until the end of the program.

There were several plans to upgrade the ignition hardware throughout the life of the Shuttles, but unfortunately they were all blackballed forever when the only one that made it to operation, 'intern with an acetlyene torch' (praised on paper both for its reliability and its savings in this era of NASA budget cutbacks) was associated with the Challenger disaster.