Poll

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

Component tests - 2017
3 (0.6%)
Component tests - 2018
21 (4.2%)
Integrated tests -  2017
19 (3.8%)
Integrated tests -  2018
237 (47%)
Integrated tests -  2019
181 (35.9%)
Raptor is not physically scaled up
33 (6.5%)
Never
10 (2%)

Total Members Voted: 504


Author Topic: SpaceX Raptor engine (Super Heavy/Starship Propulsion) - General Thread 1  (Read 869934 times)

Offline ZachF

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #480 on: 10/06/2017 08:38 pm »
Due to the mass of Raptor's turbomachinery and plumbing. Pipes need to be a minimum thickness to withstand the operating pressures expected in Raptor. If Raptor could be made out of CNT then it's TWR could easily reach or exceed 600.

And have you accounted for the fact that the plumbing is much shorter than Merlin 1D?

How do *you* account for your T/W number of 600? It surely sounds like a number pulled out of thin air. M1D has record breaking T/W, so what - based on existing engines - makes it likely that somehow Raptor has bested that number by over 3 times? It just isn't credible.

It’s mainly based on what was said by Elon, suppose he knows the number is 600, then he could easily say “same size engine as Merlin 1D, 3 times the thrust”. I don’t know any Raptor engine which is the same size and has 3 times the thrust
They are all bigger or have the same thrust. So why does he say that? Probably he meant by size, wheight, then it makes sense. Otherwise not

Size =/= weight. The Raptor is higher pressure, it will be denser, the metal parts much thicker, even if it's a similar physical size.

He was talking about the size of the combustion chamber, the Raptor has a higher expansion ratio though (~35 vs 16) so it's nozzle is larger (~0.9m vs ~1.3m).
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Offline John Alan

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #481 on: 10/06/2017 08:53 pm »
Really... we need to wait if or until SpaceX releases some specs at a later date TBD...

That said...
My guess of a mass of ~980kg (almost 1 metric ton) and a thrust stated at 170 to 190 metric tons
Puts Raptor in about the same thrust to weight ratio as Merlin 1D full thrust... 180 to 1
I will add my thought of "Good Enough" to this... No real need to try and beat that...  ;)
« Last Edit: 10/06/2017 08:54 pm by John Alan »

Offline ZachF

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #482 on: 10/06/2017 09:03 pm »
Really... we need to wait if or until SpaceX releases some specs at a later date TBD...

That said...
My guess of a mass of ~980kg (almost 1 metric ton) and a thrust stated at 170 to 190 metric tons
Puts Raptor in about the same thrust to weight ratio as Merlin 1D full thrust... 180 to 1
I will add my thought of "Good Enough" to this... No real need to try and beat that...  ;)

I'm basing my prediction of >200:1 on this:

FF to 5:45

"So the, the Raptor Engine will be the highest thrust to weight engine, we believe, on any engine of any kind ever made" - Elon Musk.

Merlin 1D is already at ~200:1
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Offline John Alan

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #483 on: 10/06/2017 09:07 pm »
200:1 is the planned 300 bar later version... in my opinion...
« Last Edit: 10/06/2017 09:08 pm by John Alan »

Offline ZachF

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #484 on: 10/06/2017 09:10 pm »
200:1 is the planned 300 bar later version... in my opinion...

I guess we'll see....  ;D ;)
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Offline DreamyPickle

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #485 on: 10/06/2017 09:11 pm »
If Elon says at IAC 2016 on why such small engines? “similar engine size but 3 times the thrust” I asume T/W is around 600 because Merlin 1D is 200.
You're taking things way too literally. In this context "similar size" does not mean "equal mass". WTF?

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #486 on: 10/07/2017 02:48 am »
Due to the mass of Raptor's turbomachinery and plumbing. Pipes need to be a minimum thickness to withstand the operating pressures expected in Raptor. If Raptor could be made out of CNT then it's TWR could easily reach or exceed 600.

And have you accounted for the fact that the plumbing is much shorter than Merlin 1D?

How do *you* account for your T/W number of 600? It surely sounds like a number pulled out of thin air. M1D has record breaking T/W, so what - based on existing engines - makes it likely that somehow Raptor has bested that number by over 3 times? It just isn't credible.

It’s mainly based on what was said by Elon, suppose he knows the number is 600, then he could easily say “similar sized engine as Merlin 1D, 3 times the thrust”. I don’t know any Raptor engine which is the same size and has 3 times the thrust?
They are all bigger or have the same thrust. So why does he say that? Probably he meant wheight instead of size, then it makes sense, otherwise not.

But I dont know either, only that its “the highest TWR of any engine, of any kind”, so above 200.

It is similar in size to the Merlin 1D and 3 times the thrust because it's about 3 times the pressure! It is made from similar materials as the Merlin (Copper alloy and high temperature Nickel alloys) so it will weigh approximately 3 times as much because both are basically very complex pressure vessels! Hence; thrust to weight stays about the same. 

Also, I am pretty sure that ZachF's rough sketch of the propellant flow is correct.

John
« Last Edit: 10/07/2017 02:56 am by livingjw »

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #487 on: 10/07/2017 03:02 am »
I posted this earlier, but here is a picture showing sizes of the Demonstrator engine, the 2016 engine and the new smaller 2017 engine. The 2017 Raptor appears to be about a 15% scale up of the Demonstrator Raptor. Today I re-estimated the demonstrator engine exit diameter from the best picture we have. I think it is closer to .94 m which would make its expansion ratio closer to 25:1 instead of 26:1. I am also working up a Pc = 3000 psi engine.

John
« Last Edit: 10/07/2017 03:10 am by livingjw »

Offline RobLynn

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #488 on: 10/07/2017 03:08 am »
I wonder if any of the Raptor plumbing is carbon fiber overwrapped. It sure saves a lot of mass in COPVs, and not all the fluid flows are high temp.

No chance, too much mismatch in thermal expansion coefficients, near impossible to do wrapping due to poor accessibility, potential fire danger around oxygen, and carbon fibre doesn't have the ability to handle more than about 200-250°C during reentry.
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #489 on: 10/07/2017 03:12 am »
I wonder if any of the Raptor plumbing is carbon fiber overwrapped. It sure saves a lot of mass in COPVs, and not all the fluid flows are high temp.

No chance, too much mismatch in thermal expansion coefficients, near impossible to do wrapping due to poor accessibility, potential fire danger around oxygen, and carbon fibre doesn't have the ability to handle more than about 200-250°C during reentry.
Carbon-carbon, on the other hand...
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Offline rakaydos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #490 on: 10/07/2017 04:14 am »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

Offline DJPledger

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #491 on: 10/07/2017 11:44 am »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Offline Kaputnik

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #492 on: 10/07/2017 01:16 pm »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Given it is a full regen nozzle, you'd need to set up the plumbing to allow this (upper and lower circuits?) and have valves that shut off in an emergency- otherwise you'll be spewing unburned fuel into the exhaust, within the relatively enclosed interstage area. I'd imagine the base heating would ramp up extremely quickly in this scenario, limiting how long you could burn the RapVacs.
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Offline rakaydos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #493 on: 10/07/2017 02:44 pm »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Given it is a full regen nozzle, you'd need to set up the plumbing to allow this (upper and lower circuits?) and have valves that shut off in an emergency- otherwise you'll be spewing unburned fuel into the exhaust, within the relatively enclosed interstage area. I'd imagine the base heating would ramp up extremely quickly in this scenario, limiting how long you could burn the RapVacs.
Keep in mind spewing unburnt fuel isnt exactly a drawback when you're struggling to raise your TWR as quickly as possible.

Offline Kaputnik

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #494 on: 10/07/2017 02:53 pm »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Given it is a full regen nozzle, you'd need to set up the plumbing to allow this (upper and lower circuits?) and have valves that shut off in an emergency- otherwise you'll be spewing unburned fuel into the exhaust, within the relatively enclosed interstage area. I'd imagine the base heating would ramp up extremely quickly in this scenario, limiting how long you could burn the RapVacs.
Keep in mind spewing unburnt fuel isnt exactly a drawback when you're struggling to raise your TWR as quickly as possible.

But it wouldn't contribute to thrust, it would be ejected from the severed regen channels and burn somewhere behind the vehicle.
It would also cut off cooling to the remaining part of the nozzle and the chamber, leading to very rapid engine failure.
So any sort of jettisonable nozzle is going to have to address this anyway by redirecting the coolant pathway.

Edited to add: simply chopping off the nozzle would actually lower T:W because all that fuel is lost rather than going to the combustion chamber. So I would assert that even if it is only for use in dire emergencies, it is essential that any sort of nozzle jettison capability must be accompanied by a redirect of the regen pathway. Not impossible, I'm sure, just an added complication.
« Last Edit: 10/07/2017 02:57 pm by Kaputnik »
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Offline RedLineTrain

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #495 on: 10/07/2017 10:01 pm »
Raptor is on the path of needing to exceed LM ASC engine reliability. That's a tall order to fill. (If those point to point transport on Earth graphics are "real", likely engine reliability would have to approach commercial transport turbofan reliability, which is three orders plus of magnitude higher.) To prove this would require extreme testing/use/reuse.

One could "concern troll" that if AJR/BO can't test to such, then SX couldn't ever do such, omitting the fact that they seem to be able to meet reliability margins above industry norms.

Copying this over from another thread, I always assumed that SpaceX tested Merlin 1D extensively development versus industry norms.  But as I posted above, Merlin 1C 's development program was about 3,000 seconds of firing.  I'm taking a look at the SSME Block III upgrade proposal, which quoted 38,000 seconds of firing.

What are the industry norms on development testing?  Was the SSME Block III proposal especially gold-plated?  Or do some substitute testing of production engines for development testing -- i.e., like I assume SpaceX did with Merlin 1D?

Offline Space Ghost 1962

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #496 on: 10/07/2017 10:54 pm »
What are the industry norms on development testing?  Was the SSME Block III proposal especially gold-plated?  Or do some substitute testing of production engines for development testing -- i.e., like I assume SpaceX did with Merlin 1D?

Some things to educate yourself with:

Test and Evaluation Guideline for Liquid Rocket Engines

Liquid Rocket Engine Flight Certification

In general, look at the acceptance criteria of contracts for vehicles engines.

Offline groundbound

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #497 on: 10/08/2017 05:46 am »
What are the industry norms on development testing?  Was the SSME Block III proposal especially gold-plated?  Or do some substitute testing of production engines for development testing -- i.e., like I assume SpaceX did with Merlin 1D?

Some things to educate yourself with:

Test and Evaluation Guideline for Liquid Rocket Engines

Liquid Rocket Engine Flight Certification

In general, look at the acceptance criteria of contracts for vehicles engines.

Very interesting, thanks. One thing I picked up is "Testing should demonstrate margin on maximum specified operating life." If you read that literally and simplistically, then all the claims for BFR booster design life imply an extremely long test program.

I'm guessing that there are other ways to verify that particular margin than 400,000 sec (or whatever) of test time.  :o 

Offline Peter.Colin

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #498 on: 10/08/2017 07:36 am »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

Offline AncientU

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #499 on: 10/08/2017 01:50 pm »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

The latest version of Merlin (M-1D) is a standard engine with upgrades for human rating the Falcon 9.  It is basically the same mass engine AFAIK.  The test to 145% power was a validation of margin, I believe, not a new rating for the engine or even a planned operating 'option.'
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