Author Topic: Merlin Engine Reusability  (Read 8682 times)

Offline Brovane

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Merlin Engine Reusability
« on: 02/26/2015 08:38 pm »
I apologize if this is already been talked about.

Does anyone have any thoughts about what design elements are incorporated into the Merlin Engine to allow easy reusability?  From what I know, rocket engines are precision engineered pieces of equipment that are treated carefully.  This means that even after a test, the rocket engines will be examined carefully again.   I think the F1 engine after a test fire was flushed out with a chemical to prevent soot buildup.  What is it about the Merlin Engine that allows the engine to be kind of roughly handled?  It seems like no special pre-cautions are taken with the engine after the pad static test fire.  Didn't the SSME require it to be fully examined after each firing?  The Merlin engine even after a brief fire after a pad abort, SpaceX had no problem with trying to re-cycle and try again for launch.  The Merlin Engine jus seems fairly robust and has the ability to go through multiple firing cycles without any type of special treatment from what I have observed.   
"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

Offline S.Paulissen

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Re: Merlin Engine Reusability
« Reply #1 on: 02/27/2015 04:30 am »
Much of how things are treated revolve around how much risk you're willing to take.  I suspect that's the largest driver of any difference in treatment.  That being said  I'm not sure a lot of claims are true.
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Offline Nomadd

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Re: Merlin Engine Reusability
« Reply #2 on: 02/27/2015 08:53 am »
 I do know that there's been a lot of bitching from engineers about Elon's insistence on reusability at every stage greatly complicating the design and manufacture of the engines. Making a turbopump 99.9% reliable for 50 firings is no small deal.
 Since that many uses, as opposed to a test fire or two, is a new thing, I'm sure the type and level of inspection and refurbishment is still to be determined to a large extent, since they can't reproduce a lot of flight conditions on the test stand. Things like soot buildup can be handled by prevention, cleaning or tolerance. Or any or all of the above.
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Offline cambrianera

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Re: Merlin Engine Reusability
« Reply #3 on: 02/27/2015 10:28 am »
TRW farmed-out the fabrication of the engine and its supporting structure, less the injector that they fabricated themselves, to a "job-shop," commercial steel fabricator located near their facility. The contract price was $8,000. Two TRW executives visited the facility to observe the fabrication process. They found only one individual working on the hardware, and when queried, he did not know nor care that he was building an aerospace rocket engine. This encounter was told and retold to emphasize the vast dissimilarity with typical aerospace attitudes and procedures.

TRW later received an Air Force contract to provide an engine for test at its rated thrust of 250,000 pounds. The test was successfully conducted at their rocket test facilities at Edwards AFB.

I had arrived late to witness the test, and only saw the firing. I was told by others who witnessed the entire test procedure that the engine was pulled out of outdoor storage where it lay unprotected against the elements. Before it was placed on the launch stand, the test crew dusted off the desert sand that had clung to it. This unplanned inclusion of a bit of an environmental test also demonstrated hardware ruggedness of the kind no other liquid rocket engine could approach.


From http://www.quarkweb.com/nqc/lib/speccoll/Schnitt/970515.html

TRW lead engineer for rocket engines was Tom Mueller.
Oh to be young again. . .

Offline starsilk

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Re: Merlin Engine Reusability
« Reply #4 on: 02/27/2015 03:08 pm »
pintle injector? much more robust than the normal shower head style.

Offline Brovane

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Re: Merlin Engine Reusability
« Reply #5 on: 02/27/2015 05:51 pm »
I do know that there's been a lot of bitching from engineers about Elon's insistence on reusability at every stage greatly complicating the design and manufacture of the engines. Making a turbopump 99.9% reliable for 50 firings is no small deal.
 Since that many uses, as opposed to a test fire or two, is a new thing, I'm sure the type and level of inspection and refurbishment is still to be determined to a large extent, since they can't reproduce a lot of flight conditions on the test stand. Things like soot buildup can be handled by prevention, cleaning or tolerance. Or any or all of the above.

I seems to me that SpaceX is trying to treat the Merlin Engine as more like a jet engine.  You inspect but you also run the engine before take-off, to verify function.  You have engine redundancy that even in the event of engine loss the vehicle can still perform it's flight. 

How do you prevent soot buildup in a rocket engine? 
"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

Offline edkyle99

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Re: Merlin Engine Reusability
« Reply #6 on: 02/27/2015 06:45 pm »
I apologize if this is already been talked about.

Does anyone have any thoughts about what design elements are incorporated into the Merlin Engine to allow easy reusability?  From what I know, rocket engines are precision engineered pieces of equipment that are treated carefully.  This means that even after a test, the rocket engines will be examined carefully again.   I think the F1 engine after a test fire was flushed out with a chemical to prevent soot buildup.  What is it about the Merlin Engine that allows the engine to be kind of roughly handled?  It seems like no special pre-cautions are taken with the engine after the pad static test fire.  Didn't the SSME require it to be fully examined after each firing?  The Merlin engine even after a brief fire after a pad abort, SpaceX had no problem with trying to re-cycle and try again for launch.  The Merlin Engine jus seems fairly robust and has the ability to go through multiple firing cycles without any type of special treatment from what I have observed.   
I don't believe that Merlin 1D is treated much differently than the Rocketdyne and Aerojet engines that powered Jupiter, Thor, Atlas, and Titan.  Those were all static tested on their launch pads during the early years and launched a few days later.  SSME is a different animal.  Some of the early H-1 powered Saturn stages were repeatedly test fired at MSFC or Mississippi, with relatively short gaps between (days).  F-1 was also a different animal, but like SSME some of those engines were repeatedly fired. 

Of course back then they could just flush the engine with lots of TCE after a test firing.   

 - Ed Kyle
« Last Edit: 02/27/2015 06:54 pm by edkyle99 »

Offline cambrianera

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Re: Merlin Engine Reusability
« Reply #7 on: 02/27/2015 06:47 pm »
How do you prevent soot buildup in a rocket engine?
a) avoiding to make soot
b) if you make it, moving it downstream, as smoothly as possible.

Point a) is of paramount importance for pyrolytic soot from RP-1 in cooling channels.
Point b) is important in TPA and in combustion chamber.
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Offline The Roadie

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Re: Merlin Engine Reusability
« Reply #8 on: 02/28/2015 01:27 am »
They've reduced the tendency to coke in the Raptor by going to methalox.
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Offline cambrianera

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Re: Merlin Engine Reusability
« Reply #9 on: 02/28/2015 09:36 am »
Shades of Paul Harvey. Great post Cambrianera.
Thanks for the appreciation.
First time I read those lines I was truly amazed, from then I had no more doubts: clever engineering is getting good performances from simpler design.
And really history of big dumb booster is a fundamental lesson of the KISS principle.
One (not minor) nitpick.
TRW main business was (and is) automotive components.
Compare automotive to aerospace and you find:
-higher investments (due to the bigger consumer base);
-higher attention to reliability (paramount on safety issues, still important on performance);
-lower care for pure performance (except for specialty car and races);
-a dynamic environment, with many players, lot of small niches and lot of competition.
 
Oh to be young again. . .

Offline john smith 19

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Re: Merlin Engine Reusability
« Reply #10 on: 03/01/2015 05:45 pm »
From http://www.quarkweb.com/nqc/lib/speccoll/Schnitt/970515.html

TRW lead engineer for rocket engines was Tom Mueller.
Schnitt was the original "big Dumb Booster" guy and his articles make interesting reading. He credited his boss with the line that "Cutting costs by a 1/2 or 2/3's won't cut it as prgramme inflation will eat any savings."

Which is exactly what has happened with the EELV programme.

I wonder if anyone's noticed the price rises over time in the launch industry.

It's called inflation, just like the kind people have to deal with in the US economy, but bigger.

I wonder what LV price inflation is now? 20% 30% PA?

BTW Decades later TRW did a pressure fed LH2/LO2 engine at 250K Lb as well under a (small) NASA contract. Worked fine as well.  The Pintle tech is rugged, although I always wonders if the JPL "impinging sheet" injectors would have been as good. They seem to have just faded away.  :( .

[EDITs for spelling]
« Last Edit: 03/02/2015 07:14 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Wetmelon

Re: Merlin Engine Reusability
« Reply #11 on: 03/02/2015 04:13 pm »
"Impinging Sheet"? Got a link to any docs on that?

Offline john smith 19

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Re: Merlin Engine Reusability
« Reply #12 on: 03/02/2015 07:31 pm »
"Impinging Sheet"? Got a link to any docs on that?
Not particularly. They were the outcome of a long programme at JPL for an efficient high throttling design for planetary probes. My impression was that the JPL programme was one of the most systematic from first principles approaches I've seen, factoring the feed system as much as the injectors themselves.

The various reports were on NTRLS but I'm not sure if anything but the "tech briefs" description is left  :(

You need to keep in mind that at the time (the 1960's) the Pintle injector was both proprietary to TRW and the patents were classified (IIRC they weren't de classified until 1972).

The impinging sheet design used a largish number of injectors which could (with suitable valving) be shut down. 10 to 1 was viewed as feasible.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

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