
SpaceX Raptor: Methane fueled full-flow staged combustion cycle engine - dpifke
https://everydayastronaut.com/raptor-engine/
======
_ph_
While the article was focused on the Raptor engine, it shows how great an
engine the RS-25 of the space shuttle was. It was crazy expensive, but as the
shuttle was reused, one could justify the cost. The sad thing is, this engine
will be used in the SLS - with no reuse what so ever. If anything describes
the insanity of the SLS system, then this. They are flying the most expensive
rocket engine ever in fully disposable mode. Even worse. After ending the
shuttle program, the engines were of course preserved, so at least the first
SLS flights are going to waste the origininal shuttle engines.

~~~
zaroth
NASA just constantly boxes itself into corners like these, going with the
“least worst” option.

Here’s an interesting article talking about how they came to the conclusion
that the RS-25 was the only way to go;

[https://www.nasaspaceflight.com/2016/01/nasa-defends-
restart...](https://www.nasaspaceflight.com/2016/01/nasa-defends-restart-
rs-25-production/)

~~~
stupidcar
Does NASA have any choice? It seems like the political environment in which
they operate makes it essentially impossible to pursue any kind of sane long-
term strategy.

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ncmncm
Seems like with as many F1s as were used on each Apollo mission, he should
count more than 17 flights. Also, I know at least one F1 was shut down before
reaching orbit.

But, wow, what a great presentation! None of the other explanations I read of
the full-flow design were anywhere near as clear and comprehensible. My
understanding of rocket design principles has taken a great leap.

~~~
cfaulkingham
If we're using that logic then there are also 9 Merlin engines on each Falcon
9 and 3 RS-25's on each shuttle.

~~~
russdill
10 per mission, don't forget the 2nd stage. And 28 per FH mission.

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avmich
> The RD-170 actually produced more thrust than the F-1, but since it barely
> ever flew, I figured it wasn’t as relevant in this line up, figured it’s
> better to go with engines that have actually been used, a lot!

Wikipedia lists some 84 launches - including a dozen of failures - of Zenit,
which uses RD-171 on the first stage - the near-twin of RD-170. That's a lot
of launches.

~~~
francislavoie
That was pointed out to him here:
[https://www.reddit.com/r/spacex/comments/bsy6rp/a_deep_rundo...](https://www.reddit.com/r/spacex/comments/bsy6rp/a_deep_rundown_on_the_raptor_engine_explaining/eosasto/?context=8&depth=9)

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simo_dax
> Enthalpy is basically the relationship between volume, pressure and
> temperature

I appreciate the non-technical approach to the subject, but this is false.
Enthalpy is an energy, it accounts for both internal energy (heat) and work.

~~~
manuka
Enthalpy is energy required to create a system. Internal energy required to
make up the system (to bring it's internals to given Temperature, pressure
ect), but there is additional work needed to position the system in the
universe (that is, to free some space for it, like moving (working on) water
or air to place the system of volume V in it).

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abledon
One of the best technical and easily digestible articles I've read in years

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marktangotango
If I ever get to ask Elon an ama question it’d be this; in the beginning the
Merlin was ablative chamber and nozzle, I thought SpaceX was going the sea
dragon/big dumb booster route. Contrast with today inparticularly the raptor,
they’re pushing the state of the art. Why the change?

~~~
_Microft
My take on an answer: they knew that they'd have to create a working rocket in
just a handful of attempts (turned out that they'd hardly had money for the
fourth - the first successful - attempt). An ablatively cooled nozzle was the
easiest way to solve the nozzle-cooling problem and they deferred work on a
more sustainable method to later.

Other pragmatic solutions were for example that the booster and upper stage
have the same diameter so that the same tooling could be used. Or that the
diameter of the stages is 12 feet because that's the maximum diameter that
could be easily and cheaply transported by road to the launch site.

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mrfusion
Very counter intuitive that all of the fuel and oxidizer goes through the
preburner yet so elegant.

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Pulletwee12549
How does the Raptor solve the coking problem in the fuel rich pre burn
chamber?

~~~
gruturo
By using methane instead of kerosene.

Methane won't cause soot/coking.

~~~
paul_f
My analysis is probably wrong, but anyway, Methane is CH4. There is one carbon
atom to 4 hydrogen atoms. RP1, or Kerosene, is a mix of different chemicals,
but the ratio is roughly one carbon atom for every two hydrogen atoms. So,
with Methane, there is less carbon to be converted to CO2 or left as soot for
the same amount of hydrogen.

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aj7
Great post! Read it beginning to end.

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yeahitslikethat
Is this Why there is a methane surge?
[https://news.ycombinator.com/item?id=20012612](https://news.ycombinator.com/item?id=20012612)

~~~
Tuna-Fish
No. The quantities of methane touched by SpaceX are low by something like 10
orders of magnitude, and they _burn_ their methane, rather than releasing it
to the air.

