Poll

When will full-scale hot-fire testing of Raptor begin?

Component tests - 2017
3 (0.6%)
Component tests - 2018
21 (4.3%)
Integrated tests -  2017
17 (3.5%)
Integrated tests -  2018
236 (48.8%)
Integrated tests -  2019
168 (34.7%)
Raptor is not physically scaled up
32 (6.6%)
Never
7 (1.4%)

Total Members Voted: 484


Author Topic: SpaceX Raptor engine (Super Heavy/Starship Propulsion) - General Thread 1  (Read 594765 times)

Offline HVM

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New Drawing comparison:

BE-4, Raptor, Merlin, SSME, NK-33, RD-180, Prometheus, and yes even a Rutherford for good measure  8)

That Rutherford looks cute compared to all the big engines. Also interesting to see how big the RS-25 was, considering its thrust & chamber pressure.

Big engines? He hasn't drawn the F1 yet.  ;^)

New Drawing comparison:

BE-4, Raptor, Merlin, SSME, NK-33, RD-180, Prometheus, and yes even a Rutherford for good measure  8)

Insane :D In case you're bored, how about adding an F1-engine?

Not enough room left to fit it on the paper...  ;D
I removed copyrighted parts and added NASA Public Domain F-1...
(I hope I get scale right; height 5.8 m )

Online cuddihy

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You do have to wonder if the unstated part of “(as expected)” is “but not as hoped.”

It’s doubtful they actually already intended to test to destruction after so few runs, especially when they need three tested to operational readiness for BFH in just a couple months.

Elon does appear to be worried that performance for Raptor may not improve at fast enough rate to overcome any weight budget challenges Raptor or Starship has getting built.

Offline envy887

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You do have to wonder if the unstated part of “(as expected)” is “but not as hoped.”

It’s doubtful they actually already intended to test to destruction after so few runs, especially when they need three tested to operational readiness for BFH in just a couple months.

Elon does appear to be worried that performance for Raptor may not improve at fast enough rate to overcome any weight budget challenges Raptor or Starship has getting built.

Maybe. But there is a reason to find out what it can't do early on, rather than taking a lot of time characterizing what it can do: if it ultimately falls short, you've wasted that time.

Online ZachF

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New Drawing comparison:

BE-4, Raptor, Merlin, SSME, NK-33, RD-180, Prometheus, and yes even a Rutherford for good measure  8)

That Rutherford looks cute compared to all the big engines. Also interesting to see how big the RS-25 was, considering its thrust & chamber pressure.

It's also a sustainer stage, hence the big nozzle. The thrust chamber itself is only about a meter in diameter (don't quote me on that, just eye balling the hardware)

It's actually much less than that, there is just a lot of equipment surrounding it. The throat is about 0.29m, the entire combustion chamber is probably ~0.5m wide.

artist, so take opinions expressed above with a well-rendered grain of salt...
https://www.instagram.com/artzf/

Offline Davidthefat

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New Drawing comparison:

BE-4, Raptor, Merlin, SSME, NK-33, RD-180, Prometheus, and yes even a Rutherford for good measure  8)

That Rutherford looks cute compared to all the big engines. Also interesting to see how big the RS-25 was, considering its thrust & chamber pressure.

RS-25 is a sustainer stage, meaning the nozzle is expanded out much higher than the boost stage engines.

Having stood next to the thrust chamber it's not all that much bigger than a merlin's. F1 on the other hand...


Edit: the RS 68 is a big boy too.
« Last Edit: 02/21/2019 08:53 pm by Davidthefat »

Online abaddon

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You do have to wonder if the unstated part of “(as expected)” is “but not as hoped.”

It’s doubtful they actually already intended to test to destruction after so few runs, especially when they need three tested to operational readiness for BFH in just a couple months.
From a previous tweet:

https://twitter.com/elonmusk/status/1094790663646760961

Quote
Propellant was not deep cryo. CH4 & O2 were just barely below liquid temp at 1 bar. In theory, Raptor should do ~300 bar at deep cryo, provided everything holds together, which is far from certain. However, only 250 bar is needed for nominal operation of Starship/Super Heavy.

We can imagine that the pressure was higher than the previously announced level, although how close it was to 300 we do not know.  It is plausible that they did in fact push it to see how far it could go, knowing that there was a good chance it would break.

Offline philw1776

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You do have to wonder if the unstated part of “(as expected)” is “but not as hoped.”

It’s doubtful they actually already intended to test to destruction after so few runs, especially when they need three tested to operational readiness for BFH in just a couple months.

Elon does appear to be worried that performance for Raptor may not improve at fast enough rate to overcome any weight budget challenges Raptor or Starship has getting built.

Huh?  Thrust is already higher than needed to toss 100T to LEO running the rocket equation and assuming a heavy Starship even though Elon said it's lighter.  And if something yet unexpected falls short, it's 80 or 90 tonnes worst case each launch.
"It'll bang right out!"

Offline TomH

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I removed copyrighted parts and added NASA Public Domain F-1...

Who remembers the M-1? (Thanks to Blackstar for posting this awhile back). And no, that M does not stand for Merlin.



« Last Edit: 02/21/2019 11:47 pm by TomH »

Offline ThePonjaX

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I'm sorry to say that. You know a lot about rocket engines guys but it's really hard to follow a thread about the Raptor and the news about it when it's full of diagrams which a lot of cases aren't related to the Raptor.

Offline HVM

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I'm sorry to say that. You know a lot about rocket engines guys but it's really hard to follow a thread about the Raptor and the news about it when it's full of diagrams which a lot of cases aren't related to the Raptor.

Tom Müller and other Elven-smiths are forging Twi~Essɛn right now, but it takes some time before that bird of prey expels its fire from its gullet and out of its mouth... So we need to entertain ourselves some how.

Online Lars-J

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I'm sorry to say that. You know a lot about rocket engines guys but it's really hard to follow a thread about the Raptor and the news about it when it's full of diagrams which a lot of cases aren't related to the Raptor.

Tom Müller and other Elven-smiths are forging Twi~Essɛn right now, but it takes some time before that bird of prey expels its fire from its gullet and out of its mouth... So we need to entertain ourselves some how.

Yes, but the valid point is that general engine discussion does not need to happen in THIS thread. Show some consideration. When people subscribe to to threads they get emails for every reply.

Offline Okie_Steve

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You do have to wonder if the unstated part of “(as expected)” is “but not as hoped.”

It’s doubtful they actually already intended to test to destruction after so few runs, especially when they need three tested to operational readiness for BFH in just a couple months.

Elon does appear to be worried that performance for Raptor may not improve at fast enough rate to overcome any weight budget challenges Raptor or Starship has getting built.

Maybe. But there is a reason to find out what it can't do early on, rather than taking a lot of time characterizing what it can do: if it ultimately falls short, you've wasted that time.
My guess would be they learned something important on the first runs that immediately got incorparated into sn2 and would make further testing of that part of the design less useful so they decided to stress some other parts hard since sn2 is coming soon

Online Lars-J

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With regard to the end of the SN1 engine and the testing campaign, this is somewhat speculative but bear with it.

There were several issues, at least that is the perception, with the SN1 engine. Some were expected, some weren't. Right now the big one, at least from what we can gather externally and what many on this forum observed, is ISP. That is, the fuel efficiency. SpaceX was looking to reach 380 or even higher if possible, it now appears what they actually got was quite a bit lower but by how much we don't know. This is due to the film cooling problem. On the first test they did not have adequate film cooling and vaporized a small amount of the copper chamber liner. This would have become a large amount in a sustained MDC length test, but it was not terribly significant since these tests were very short.

I'm sorry, but what do you base that on? What have we been told to indicate a significant ISP shortfall? What observations support this?

Because if you can't source that, the rest of your lengthy post is even less based in reality.
« Last Edit: 02/22/2019 06:54 am by Lars-J »

Offline Stan-1967

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With regard to the end of the SN1 engine and the testing campaign, this is somewhat speculative but bear with it.

There were several issues, at least that is the perception, with the SN1 engine. Some were expected, some weren't. Right now the big one, at least from what we can gather externally and what many on this forum observed, is ISP. That is, the fuel efficiency. SpaceX was looking to reach 380 or even higher if possible, it now appears what they actually got was quite a bit lower but by how much we don't know. This is due to the film cooling problem. On the first test they did not have adequate film cooling and vaporized a small amount of the copper chamber liner. This would have become a large amount in a sustained MDC length test, but it was not terribly significant since these tests were very short.

There is zero chance that SpaceX was expecting an ISP of 380 for this engine & expansion ratio.  The target would be more 340 ish.  Chamber pressure is more key in getting the T/W they want, they are already pretty far up the ISP vs. chamber pressure curve above 200 bar so that ISP is more incremental.  Others correct me if I am wrong please, but the ISP is not linear to chamber pressure, whereas thrust is more proportional to chamber pressure in that is is the first order determining factor in the mass flow rate.

Way too much concern for such limited information.

Offline niwax

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With regard to the end of the SN1 engine and the testing campaign, this is somewhat speculative but bear with it.

There were several issues, at least that is the perception, with the SN1 engine. Some were expected, some weren't. Right now the big one, at least from what we can gather externally and what many on this forum observed, is ISP. That is, the fuel efficiency. SpaceX was looking to reach 380 or even higher if possible, it now appears what they actually got was quite a bit lower but by how much we don't know. This is due to the film cooling problem. On the first test they did not have adequate film cooling and vaporized a small amount of the copper chamber liner. This would have become a large amount in a sustained MDC length test, but it was not terribly significant since these tests were very short.

There is zero chance that SpaceX was expecting an ISP of 380 for this engine & expansion ratio.  The target would be more 340 ish.  Chamber pressure is more key in getting the T/W they want, they are already pretty far up the ISP vs. chamber pressure curve above 200 bar so that ISP is more incremental.  Others correct me if I am wrong please, but the ISP is not linear to chamber pressure, whereas thrust is more proportional to chamber pressure in that is is the first order determining factor in the mass flow rate.

Way too much concern for such limited information.

Their stated targets for a future production iteration of Raptor were 330s SL and 380s vac. But they have made it clear that the vacuum engine is some ways off, and looking at Merlin Vac with its 140+ ER it will be significantly different from the thing currently on the test stand. The current first version of Starship has also explicitly been designed to have SL engines on the first stage for now, so I don't really see the issue.
Which booster has the most soot? SpaceX booster launch history! (discussion)

Online uhuznaa

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With regard to the end of the SN1 engine and the testing campaign, this is somewhat speculative but bear with it.

There were several issues, at least that is the perception, with the SN1 engine. Some were expected, some weren't. Right now the big one, at least from what we can gather externally and what many on this forum observed, is ISP. That is, the fuel efficiency. SpaceX was looking to reach 380 or even higher if possible, it now appears what they actually got was quite a bit lower but by how much we don't know. This is due to the film cooling problem. On the first test they did not have adequate film cooling and vaporized a small amount of the copper chamber liner. This would have become a large amount in a sustained MDC length test, but it was not terribly significant since these tests were very short.

There is zero chance that SpaceX was expecting an ISP of 380 for this engine & expansion ratio.  The target would be more 340 ish.  Chamber pressure is more key in getting the T/W they want, they are already pretty far up the ISP vs. chamber pressure curve above 200 bar so that ISP is more incremental.  Others correct me if I am wrong please, but the ISP is not linear to chamber pressure, whereas thrust is more proportional to chamber pressure in that is is the first order determining factor in the mass flow rate.

Way too much concern for such limited information.

I think the concern about having to dial up film cooling is that it means you're dumping more unburned fuel out of your nozzle and this is diametral to maximizing ISP.

Offline 50_Caliber

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I wonder how fast can SpaceX iterate a design? Could they have tested version 1.0 then incorporate design changes into the next one and be testing version 2.0 the next week or two?

Online Chris Bergin

Going to let this go to 100 pages - just because it's a great thread - and then move to the "Thread 2" on this, so that'll be this weekend.

Remember, massive threads can go a bit off topic at times, so let's keep it focused on Raptor. (A few report to mods - letting it slide per the next thread incoming).

Offline sevenperforce

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I think the concern about having to dial up film cooling is that it means you're dumping more unburned fuel out of your nozzle and this is diametral to maximizing ISP.
No unburned fuel is dumped.

Offline OxCartMark

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I think the concern about having to dial up film cooling is that it means you're dumping more unburned fuel out of your nozzle and this is diametral to maximizing ISP.
No unburned fuel is dumped.

?

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