SpaceX ‘Mars’ rocket engine tested - BBC News
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Yes yes yes! This is super exciting news.
If being an engine that takes us to Mars wasn’t enough, it’s also an engine that’s being designed around reusability and high efficiency. It’s a FFSC engine or Full flow staged combustion. It turns out that only 3 FFSC engines have ever been test fired, including raptor, and none have ever been flown. I’m not sure if you guys want details, but basically both all of the fuel and oxidizer run through their own preburner to spin the turbine for their respective pumps(hence full flow). Normally, a bit of oxidizer and fuel is siphoned off to the pre-burner(burns a bit of the mix to create power to spin turbopumps for fuel and oxidizer) while the majority flows straight to the combustion chamber. This difference allows the turbopumps to run at lower RPMS and cooler temps apparently due to the increased mass flow but I’m not sure on the the why of that.
hey are also methalox which burns cleanly(almost or as clean as hydrolox, unsure) and I’m pretty sure it’s one of the few methalox engines ever to be test fired as well. Methalox is great for many reasons. Methane is more dense than hydrogen while not being quite as efficient in the combustion process. The trade-off is that you can store more of it easier. Hydrogen is a bitch to contain and we haven’t really solved the problem of containing it for months on a spacecraft…Like hydrogen, methane won’t leave any soot in the engines and burns with a greater specific impulse than RP-1(kerosene) which will become a necessity in the age of truly reusable rockets.
Basically, these engines are fuckin’ rad. They’re not just engines that will take us to Mars. They are the engines designed and built for the future using tech that hasn’t been flown before. These engines are pushing multiple boundaries at once. I’m really excited for tomorrow.
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Oh my god how do you know all of these details it’s awesome (of course we need details). Did you already work on this type of rocket ?
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I wish! I’m working now to break into the field…getting an entry level job with no experience in aerospace without an aerospace degree is tough.
Just a healthy dose of obsession and wikipedia. I know the gist offhand but something like the details of how a FFSC engine works is something I had to lookup to remind myself.
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I think this is because of a few related reasons (but I’m not a rocket engineer, so I could well be totally wrong). Since all the exhaust of the turbopump goes into the combustion chamber (rather than being wasted overboard) you can have a much more powerful turbopump. Because the turbopump is more powerful you can pump more liquid around. Turbopumps are primarily cooled by the liquid they’re pumping so more mass flow means more coolant and a lower overall temperature.
There are a couple of other benefits too. For example you can also drive far higher chamber pressures, which is an important factor in rocket engine efficiency - raptor operates at 30MPa! Additionally because the fuel/oxidizer is fully gas and very well mixed you get more complete combustion which again leads to a more efficient engine.
methalox which burns cleanly(almost or as clean as hydrolox, unsure)
This reminds me of a really fascinating video about CFD at spacex. They mention in it how methane is a relatively complex chemical reaction when combusted. Here’s the specific timestamp where they talk about the chemistry although I suspect you guys may be interested in the rest of the video 
Basically, these engines are fuckin’ rad.
+1
I’m super excited to see what Elon has to say tomorrow 
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This is actually the definition of a closed cycle engine. The vast majority of rocket engines are open cycle engines where the turbopump exhaust is dumped(included SpaceX’s Merlin engines). I’m pretty sure the first closed cycle engine was the nk-33 built by the Russians for the N-1; their answer to the Saturn-V. You are correct on the assumption that the closed cycle engines increase the chamber pressure and efficiency of the engine. Not only does higher chamber pressure = higher thrust and specific impulse, you also have the extra mass flowing out of the engine rather than dumping it over beard. Thrust is just Massflow*exhaust velocity afterall.
I think you might be on to one of the reasons there. I just find it counter intuitive that a higher massflow actually produces lower turbine rpms. It’s probably a simple “oh duh” fact but it’s just not obvious to me.
Another reason this engine is awesome. I couldn’t remember OTOH so I looked it up. The RD-180 which is one of Russia’s most advanced kerelox engines runs at a chambe pressure of 26.7 MPA. I’m fairly positive it is a closed cycle engine as well(fact checked), but it is not full flow. You can see in the schematic below that both fuel and oxidizer is diverted from the main combustion chamber to run the preburner(where the ehxaust of the preburner goes back into the combustion chamber, hence closed cycle), whereas in a full flown all fuel/oxidzer go to their respective preburners and then flow to the main combustion chamber.
Edit: Forgot image…
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Which is a well known problem with many rocket engines 
I think it’s simply that the pump is bigger, so it can shift more fluid at a given RPM.
Edit: I wasted most of the two hours between these posts reading about the details of turbopump design. Dammit.
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Well that makes sense…
Probably because you need less plumbing so it frees up mass to increase the size of the pump.
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Double post because I feel it’s important…the stream starts in just about 2.5 hours now. I’ll be watching it and I’ll post any pictures and details after unless you guys beat me to it during the stream.
Edit: www.spacex.com/mars
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I’ll be there digitally, I’ll wave from my side of the monitor! 
So… a video popped up just now…
If they can pull this off…
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I gotta vent my frustration. The whole last week I was trying to plan today around this and it never works. My laptop is dead, we have no AC power on board right now and I’m 10 miles off shore with spotchy service and were only out on the water for this hour only. At least I got a pretty shot of the sunrise this morning…
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beautiful.
I want this future now. Very few of use watching this today will be alive to witness this era. And that sucks.
@Skyentist that sucks as well. Are you able to still watch on your phone?
I’m trying. Did it start yet? I’m just constantly loading right now
Still says -
Live stream is starting soon
what are you off shore doing? work? etc
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Well at least that’s not just me. SpaceX a bit late as usual heh
We’re live! SpaceX FM!
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Just starting to roll pre stream now
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Had to run our boat to a nearby harbour to get new generators installed.
I took a bunch of pics last week while the forums are down I haven’t got around to posting yet though. Super pretty with glassy water it was cool.
Thanks for the heads up guys!
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