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The Tech Behind SpaceX’s New Engine

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Re: The Tech Behind SpaceX’s New Engine

#41

Post by Tuna-Fish »

Eridrus wrote: post #35
buboard wrote: post #21

Earlier quoted context omitted.

Wikipedia has some stats comparing their current engines (probably speculative for the raptor) Raptor: Thrust 1900 KN / 330 specific impulse Merlin 1D: 480KN / 275 s.i. i can't find the weight of the Raptor. Merlin is 630Kg

So, for the folks like me who don't know anything about rockets, it seems like "specific impulse" is the measure of how much "impulse" is generated per unit of fuel. So 330/275 = 20% better.

Most of that is actually because of the difference in fuel -- Raptor runs on Methane, which produces more H2O and less CO2 than RP-1, and H2O is a smaller molecule and therefore more efficient.

Yep. The actual physically relevant number is exhaust velocity, which is the mean velocity of the particles in the rocket exhaust.

Isp = Specific Impulse = exhaust velocity/(9.81ms^-2).

9.81ms^-2 there is not any actual acceleration, just an agreed conversion factor. The unit of Isp has no physical significance, the convention just arose because early rocketry was a collaboration of people who all used different units, and they wanted to be able to compare numbers. Since the unit they all shared was a second, and they all agreed (roughly) on the real value of g, they just divided exhaust velocity by their g to get a number that could be compared. The convention stuck.

Re: The Tech Behind SpaceX’s New Engine

#42

Post by [deleted] »

Tuna-Fish wrote: post #41
Eridrus wrote: post #35

Earlier quoted context omitted.

So, for the folks like me who don't know anything about rockets, it seems like "specific impulse" is the measure of how much "impulse" is generated per unit of fuel. So 330/275 = 20% better.

Most of that is actually because of the difference in fuel -- Raptor runs on Methane, which produces more H2O and less CO2 than RP-1, and H2O is a smaller molecule and therefore more efficient. Yep. The actual physically relevant number is exhaust velocity, which is the mean velocity of the particles in the rocket exhaust. Isp = Specific Impulse = exhaust velocity/(9.81ms^-2). 9.81ms^-2 there is not any actual accele…

[deleted]

Re: The Tech Behind SpaceX’s New Engine

#43

Post by elif »

clanrebornsx wrote: post #26
jlv2 wrote: post #18

Earlier quoted context omitted.

It is -- it's B1019. I suspect that's why they are a janitor.

Sorry I've PhD in Particle Physics. Not able to find any work, so I am doing janitor work. Why do you insult Janitor's intellect?

If you provided supporting reasoning or evidence of any kind I believe you'd have better reception. Your unqualified assertion does not resemble the statement of a scientist, and you should not be surprised that relying on an appeal-to-authority of a janitor drew ridicule.

Re: The Tech Behind SpaceX’s New Engine

#44

Post by Hypx »

mabbo wrote: post #37

> While the Space Shuttle has long since retired, a variation of the engine itself will go on to power the Space Launch System. It will be the most powerful rocket NASA has ever built and is slated to begin missions in 2020. 2020? I honestly doubt we'll see the SLS launch before 2024 at it's current rate.

They're nearly finished actually. The core stage is in final assembly. We'll probably see a launch in 2020 or 2021.

Re: The Tech Behind SpaceX’s New Engine

#45

Post by thebluehawk »

clanrebornsx wrote: post #26
jlv2 wrote: post #18

Earlier quoted context omitted.

It is -- it's B1019. I suspect that's why they are a janitor.

Sorry I've PhD in Particle Physics. Not able to find any work, so I am doing janitor work. Why do you insult Janitor's intellect?

What proof/rational do you have that it's fake?

Re: The Tech Behind SpaceX’s New Engine

#46

Post by jbkkd »

prando wrote: post #24

https://www.netflix.com/title/80119093 My rocket-science knowledge is abysmal, but I thoroughly enjoyed this article and the Netflix documentary that I have linked to was incredible. Anyone even remotely interested in rockets should check it out :).

Unavailable for me in the UK, what's the name of the documentary?

Re: The Tech Behind SpaceX’s New Engine

#47

Post by CarVac »

hoorayimhelping wrote: post #38
twic wrote: post #8

Either approach, whether it recaptures the oxidizer or fuel rich preburner exhaust, is clearly an improvement over dumping everything overboard. But neither is an ideal solution as there’s still potentially combustible products being wasted. Are there? Here's a diagram of the RD-180, which uses an oxygen-rich preburner: https://en.wikipedia.org/wiki/RD-180#/media/File:Rd180schema... Where is anything escaping other t…

The diagram doesn't show that the fuel used in the preburner is combusted less efficiently than the fuel used in the main combustion chamber. It comes out through the nozzle, but isn't fully combusted (it comes out as liquid, while the main fuels are gasses) and so is wasted energy. From what I understand, the fuel and oxidizer that has been through the preburners to spin the turbines is basically fungible with fuel…

I'm not sure where you're getting that.

If it's incompletely burned in the preburner, it gets completely burned in the combustion chamber.

And even if that were true that combustion happening in the preburner was wasted, then full-flow staged combustion would be equally bad because it still has preburners.

Re: The Tech Behind SpaceX’s New Engine

#48

Post by ff_ »

jbkkd wrote: post #46
prando wrote: post #24

https://www.netflix.com/title/80119093 My rocket-science knowledge is abysmal, but I thoroughly enjoyed this article and the Netflix documentary that I have linked to was incredible. Anyone even remotely interested in rockets should check it out :).

Unavailable for me in the UK, what's the name of the documentary?

I cannot access it as well, but it should be "Cosmodrome"

Re: The Tech Behind SpaceX’s New Engine

#49

Post by [deleted] »

wolf550e wrote: post #29
tehsauce wrote: post #23

Rocket lab's Rutherford engine uses a closed cycle with battery powered fuel pumps. They were actually to fly an engine like this in their "electron" rocket, as early as 2017. https://en.m.wikipedia.org/wiki/Rutherford_(rocket_engine)

This is only viable for small engines, like expander cycle is only viable for small engines. The specific energy of electric batteries cannot compare to that of kerolox or methalox. Closed cycle is not a new idea: https://en.wikipedia.org/wiki/Staged_combustion_cycle#Histor...

[deleted]

Re: The Tech Behind SpaceX’s New Engine

#50

Post by Gibbon1 »

Tuna-Fish wrote: post #41
Eridrus wrote: post #35

Earlier quoted context omitted.

So, for the folks like me who don't know anything about rockets, it seems like "specific impulse" is the measure of how much "impulse" is generated per unit of fuel. So 330/275 = 20% better.

Most of that is actually because of the difference in fuel -- Raptor runs on Methane, which produces more H2O and less CO2 than RP-1, and H2O is a smaller molecule and therefore more efficient. Yep. The actual physically relevant number is exhaust velocity, which is the mean velocity of the particles in the rocket exhaust. Isp = Specific Impulse = exhaust velocity/(9.81ms^-2). 9.81ms^-2 there is not any actual accele…

> 9.81ms^-2 there is not any actual acceleration, just an agreed conversion factor.

I'd look it up but my textbooks[1] are in boxes, but the units everyone uses are wrong. Actually inappropriately simplified.

[1] I have one and exactly one textbook that has the full units for gc.

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