Author Topic: SpaceX: Merlin 1D Updates and Discussion Thread 3  (Read 225548 times)

Offline Oersted

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #240 on: 05/12/2018 12:02 pm »
Indeed. It takes me months to do these videos, they are released at a slow pace.

I liked the video a lot. Very informative, great footage.

I think there is a small error at Soyuz launch. At last step before lift-off you say that the peripheral stages are at 100% and the central stage is at 70% but your graphics show all of them at 70%.

Early on your accent is just charming but a bit later on it becomes an impediment to understanding the technical phrases. Maybe speak a bit more slowly, or do some subtitles...

Offline Davidthefat

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #241 on: 05/13/2018 09:54 pm »

What makes you think that OF ratios aren't trimmed during flight? Just curious where you got your information.

[L2 link] https://forum.nasaspaceflight.com/index.php?topic=45594.msg1818987#msg1818987

I wouldn't take that statement to heart; the process that is mentioned is probably being used for an assembly that would only affect the start up and shutdown behaviors.

Offline IainMcClatchie

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #242 on: 05/14/2018 07:17 am »
Here's a plot of some of the S1 parameters for the Bangabandhu launch. They still throttle down for Max-Q, but there is a gradual reduction in throttle for each phase, giving constant thrust for each phase of the S1 burn. This would limit the thrust loading not just on the Octaweb, but the rocket as a whole.

Edit: Perhaps constant (SL max) thrust is necessary to maintain a factor of safety of 1.4 for CCP?

Okay, compressive stress in the Octaweb is a limit.  Wow.

Quick check, if the tank ullage is at 30 psi, that's 2.1 meganewtons axially, which is quite a bit less than the liftoff 7.6 meganewtons.  Looks like the first stage tank is under significant axial compressive load, at least near MECO.  I would not have expected that either.

Does anyone have real values for the first stage ullage pressure?

Offline Semmel

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #243 on: 05/14/2018 07:29 am »
Here's a plot of some of the S1 parameters for the Bangabandhu launch. They still throttle down for Max-Q, but there is a gradual reduction in throttle for each phase, giving constant thrust for each phase of the S1 burn. This would limit the thrust loading not just on the Octaweb, but the rocket as a whole.

Edit: Perhaps constant (SL max) thrust is necessary to maintain a factor of safety of 1.4 for CCP?

Okay, compressive stress in the Octaweb is a limit.  Wow.

Quick check, if the tank ullage is at 30 psi, that's 2.1 meganewtons axially, which is quite a bit less than the liftoff 7.6 meganewtons.  Looks like the first stage tank is under significant axial compressive load, at least near MECO.  I would not have expected that either.

Does anyone have real values for the first stage ullage pressure?

I dont think its a limit but rather a set procedure to fulfill human rating requirements. If the rocket is designed to have 40% contingency at launch and you dont want to exceed that contingency threshold, the rocket must throttle down. This would not be necessary for cargo launches but NASA wants 7 launches of F9 with the same limits (meaning also the same threshold margins during flight) before NASAnauts can board. In that light, the flight profile makes total sense to me.

Offline Comga

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #244 on: 07/30/2018 08:24 pm »
Just did a count
Iridium 7 launch makes it 500 Merlin engines flown since the last in-flight engine failure on CRS-1.
This includes the 9 ground lit Merlins and the MVac on the second stage.
This excludes the engines on CRS-7 that didn't get to burn for their full profile, or wasn't lit in the case of the MVac.
That's quite a record and a statistically significant history.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Doesitfloat

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #245 on: 07/30/2018 09:03 pm »
Merlin C is a different engine than Merlin D

Offline IanThePineapple

Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #246 on: 07/31/2018 02:06 am »
Just did a count
Iridium 7 launch makes it 500 Merlin engines flown since the last in-flight engine failure on CRS-1.
This includes the 9 ground lit Merlins and the MVac on the second stage.
This excludes the engines on CRS-7 that didn't get to burn for their full profile, or wasn't lit in the case of the MVac.
That's quite a record and a statistically significant history.
Might be better to skip the F9 after CRS-7 since that was the last of the M1Cs.

CRS-2 was the last flight of any M1C (end of F9 v1.0),  everything from then on have been versions of the M1D.

Offline Hominans Kosmos

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #247 on: 07/31/2018 05:57 am »
Quick check, if the tank ullage is at 30 psi, that's 2.1 meganewtons axially, which is quite a bit less than the liftoff 7.6 meganewtons .....
Does anyone have real values for the first stage ullage pressure?

Should be closer to 50, I think that was the figure Tom Mueller used in the educational video describing how Merlin and it's turbo machinery worked.

Offline Comga

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #248 on: 07/31/2018 05:59 am »
Just did a count
Iridium 7 launch makes it 500 Merlin engines flown since the last in-flight engine failure on CRS-1.
This includes the 9 ground lit Merlins and the MVac on the second stage.
This excludes the engines on CRS-7 that didn't get to burn for their full profile, or wasn't lit in the case of the MVac.
That's quite a record and a statistically significant history.
Might be better to skip the F9 after CRS-7 since that was the last of the M1Cs.

That’s a passive expression of an opinion and doesn’t change anything. “Better”?
I chose to count all Merlin’s since the last failed (boost) engine.
Work up stats on just the Merlin-1D if you want.
Can anyone say anything relevant and not pick at the methodology?
Does no one see the huge number aa an indication of reliability?
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline rpapo

Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #249 on: 07/31/2018 10:20 am »
As far as we know, there has never been a failure of a Merlin 1D, sea-level or vacuum, during the boost phase of any flight.  There have been some problems with landing burns, but that was uncharted territory at first.  There may have been failures at McGregor, but those would not be public knowledge.

Agreeing with Comga here: any way you want to look at it, the Merlin 1D has been a remarkably reliable engine.  Tom Mueller and his team can be justifiably proud of what they have done.
« Last Edit: 07/31/2018 10:22 am by rpapo »
Following the space program since before Apollo 8.

Offline JamesH65

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #250 on: 07/31/2018 11:33 am »
As far as we know, there has never been a failure of a Merlin 1D, sea-level or vacuum, during the boost phase of any flight.  There have been some problems with landing burns, but that was uncharted territory at first.  There may have been failures at McGregor, but those would not be public knowledge.

Agreeing with Comga here: any way you want to look at it, the Merlin 1D has been a remarkably reliable engine.  Tom Mueller and his team can be justifiably proud of what they have done.

Agreed. I do wonder what they have done differently to others that had resulting in this spectacular engine in such a short timeframe. Is it that they have rapid turnaround? Are they taking more `risks`? Has returning the engines from flight regimes driven change? Are they simply given a decent length of rope by Musk? Do they simply employ better people? Is design technology and simulation simply so much better now? All of the above and more?

Interesting.

Offline rsdavis9

Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #251 on: 07/31/2018 11:48 am »
Maybe computer monitoring for self check. After all tesla and spacex are run by elon musk and he started as a computer programmer. And both those companies are distinguished by their excellent computer systems.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline wannamoonbase

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #252 on: 07/31/2018 01:35 pm »
As far as we know, there has never been a failure of a Merlin 1D, sea-level or vacuum, during the boost phase of any flight.  There have been some problems with landing burns, but that was uncharted territory at first.  There may have been failures at McGregor, but those would not be public knowledge.

Agreeing with Comga here: any way you want to look at it, the Merlin 1D has been a remarkably reliable engine.  Tom Mueller and his team can be justifiably proud of what they have done.

Agreed. I do wonder what they have done differently to others that had resulting in this spectacular engine in such a short timeframe. Is it that they have rapid turnaround? Are they taking more `risks`? Has returning the engines from flight regimes driven change? Are they simply given a decent length of rope by Musk? Do they simply employ better people? Is design technology and simulation simply so much better now? All of the above and more?

Interesting.

I’ll add my 2 cents on 2 ideas why the Merlin is such a strong performer.
1) It’s using the newest technology in design and materials.
2) They’ve kept it small.  Which has given them great T/W and smaller components like the turbo pumps and combustion chambers should be easier to control and build than larger engines.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline ValmirGP

Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #253 on: 07/31/2018 01:59 pm »
As far as we know, there has never been a failure of a Merlin 1D, sea-level or vacuum, during the boost phase of any flight.  There have been some problems with landing burns, but that was uncharted territory at first.  There may have been failures at McGregor, but those would not be public knowledge.

Agreeing with Comga here: any way you want to look at it, the Merlin 1D has been a remarkably reliable engine.  Tom Mueller and his team can be justifiably proud of what they have done.

Agreed. I do wonder what they have done differently to others that had resulting in this spectacular engine in such a short timeframe. Is it that they have rapid turnaround? Are they taking more `risks`? Has returning the engines from flight regimes driven change? Are they simply given a decent length of rope by Musk? Do they simply employ better people? Is design technology and simulation simply so much better now? All of the above and more?

Interesting.

I’ll add my 2 cents on 2 ideas why the Merlin is such a strong performer.
1) It’s using the newest technology in design and materials.
2) They’ve kept it small.  Which has given them great T/W and smaller components like the turbo pumps and combustion chambers should be easier to control and build than larger engines.

My 2 cents: Maybe it is because they designed the Merlins from the start with reuse in mind and as so those engines have a higher margin in their design than one meant to be thrown away, so their reliability is a byproduct of their design goals.

Offline Robotbeat

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #254 on: 07/31/2018 02:33 pm »
As well as enabling them to test the heck out of every engine: acceptance firing of each engine, then as integrated in a stage, then as a hot fire test on the pad. Each tested three times before launch.
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Offline wannamoonbase

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #255 on: 07/31/2018 02:50 pm »
My 2 cents: Maybe it is because they designed the Merlins from the start with reuse in mind and as so those engines have a higher margin in their design than one meant to be thrown away, so their reliability is a byproduct of their design goals.

I agree, but also that makes its performance numbers and thrust to weight even more impressive.

Unlike the established companies SpaceX flies more too.  The other guys can work 10 years on an engine and never leave the ground. 
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline Kosmos2001

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #256 on: 07/31/2018 04:06 pm »
Unlike the established companies SpaceX flies more too.  The other guys can work 10 years on an engine and never leave the ground.

I do agree. The difference among other companies and SpaceX is that rocket engine engineers in SpaceX have their hands constantly dirty. Instead of freezing the first successful design, they still improving it because there is always something to make them better and they don't hesitate to make changes in a think that already works. Merlins are in constant evolution unlike other rocket engines that practically are unmodified and when they realise it is time to make something better, half of the crew that did it are already retired and new engineers may have a lot of theory but haven't touched a single rocket engine in their lives.

Offline butters

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #257 on: 07/31/2018 04:47 pm »
NASA and the traditional contractors use a different quality assurance philosophy. They use qualification test articles in combination with extensive documentation of how the test articles were produced, on the premise that subsequent articles produced in the same way (and with documentation to that effect) are qualified to fly without representative preflight testing.

SpaceX tests every engine every time, which would seem to reduce the need for such extensive documentation and adherence to qualified designs/procedures. But this is uncomfortable for NASA in the context of commercial crew.

For example, SpaceX apparently sees some "undesirable anomalies" with Merlin engines on the test stand. From SpaceX's perspective, maybe they just don't fly the particular engines that manifest the anomaly. They test all the engines and weed out any of them that aren't up to snuff. But because of the way that NASA normally operates, they are probably concerned that SpaceX may be unable to reliably build engines that are guaranteed to meet requirements on the test stand.

If NASA made the same requirement for, let's say, Intel microprocessors used in their computer systems, Intel would say no, that's not the way the microprocessor industry works... We test everything, there's a certain yield of functional chips, they don't have uniform performance, and we "bin" them into different SKUs and price points accordingly.

Offline Comga

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #258 on: 07/31/2018 05:13 pm »
NASA and the traditional contractors use a different quality assurance philosophy. They use qualification test articles in combination with extensive documentation of how the test articles were produced, on the premise that subsequent articles produced in the same way (and with documentation to that effect) are qualified to fly without representative preflight testing.

SpaceX tests every engine every time, which would seem to reduce the need for such extensive documentation and adherence to qualified designs/procedures. But this is uncomfortable for NASA in the context of commercial crew.

For example, SpaceX apparently sees some "undesirable anomalies" with Merlin engines on the test stand. From SpaceX's perspective, maybe they just don't fly the particular engines that manifest the anomaly. They test all the engines and weed out any of them that aren't up to snuff. But because of the way that NASA normally operates, they are probably concerned that SpaceX may be unable to reliably build engines that are guaranteed to meet requirements on the test stand.

If NASA made the same requirement for, let's say, Intel microprocessors used in their computer systems, Intel would say no, that's not the way the microprocessor industry works... We test everything, there's a certain yield of functional chips, they don't have uniform performance, and we "bin" them into different SKUs and price points accordingly.

And that's the point

SpaceX has modified the manufacturing process to eliminate microcracking in the turbines, IIRC, ahead of launching for Commercial Crew, and now goes on to eliminate an "undesirable anomaly", even though they have 500 successful "booster" burns.  (When they started the CCtCap effort they were probably only at 100.  Someone could look that up.) There seems to be no point at which experience outweighs analysis, so that flying an "improved" engine with minimal flight history (70) is preferred to flying an "imperfect" engine with a hugely successful history. (500+)
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline mme

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #259 on: 07/31/2018 05:15 pm »
As far as we know, there has never been a failure of a Merlin 1D, sea-level or vacuum, during the boost phase of any flight.  There have been some problems with landing burns, but that was uncharted territory at first.  There may have been failures at McGregor, but those would not be public knowledge.

Agreeing with Comga here: any way you want to look at it, the Merlin 1D has been a remarkably reliable engine.  Tom Mueller and his team can be justifiably proud of what they have done.

Agreed. I do wonder what they have done differently to others that had resulting in this spectacular engine in such a short timeframe. Is it that they have rapid turnaround? Are they taking more `risks`? Has returning the engines from flight regimes driven change? Are they simply given a decent length of rope by Musk? Do they simply employ better people? Is design technology and simulation simply so much better now? All of the above and more?

Interesting.

According to Tom Mueller, it's at least partially because of Elon's drive for simplicity and low cost ...

Transcript of Tom Mueller's speech interview on May 2, 2017

Quote
One of the things that we did with the Merlin 1D was; he kept complaining— I talked earlier about how expensive the engine was. [inaudible] [I said,] “[the] only way is to get rid of all these valves. Because that’s what’s really driving the complexity and cost.” And how can you do that? And I said, “Well, on smaller engines, we’d go face-shutoff, but nobody’s done it on a really large engine. It’ll be really difficult.” And he said, “We need to do face-shutoff. Explain how that works?” So I drew it up, did some, you know, sketches, and said “here’s what we’d do,” and he said “That’s what we need to do.” And I advised him against it; I said it’s going to be too hard to do, and it’s not going to save that much. But he made the decision that we were going to do face-shutoff.

So we went and developed that engine; and it was hard. We blew up a lot of hardware. And we tried probably tried a hundred different combinations to make it work; but we made it work. I still have the original sketch I did; I think it was— what was it, Christmas 2011, when I did that sketch? And it’s changed quite a bit from that original sketch, but it was pretty scary for me, knowing how that hardware worked, but by going face-shutoff, we got rid of the main valves, we got rid of the sequencing computer; basically, you spin the pumps and pressure comes up, the pressure opens the main injector, lets the oxygen go first, and then the fuel comes in. So all you gotta time is the ignitor fluid. So if you have the ignitor fluid going, it’ll light, and it’s not going to hard start. That got rid of the problem we had where you have two valves; the oxygen valve and the fuel valve. The oxygen valve is very cold and very stiff; it doesn’t want to move. And it’s the one you want open first. If you relieve the fuel, it’s what’s called a hard start. In fact, we have an old saying that says, “[inaudible][When you start a rocket engine, a thousand things could happen, and only one of those is good]“, and by having sequencing correctly, you can get rid of about 900 of those bad things, we made these engine very reliable, got rid of a lot of mass, and got rid of a lot of costs. And it was the right thing to do.

And now we have the lowest-cost, most reliable engines in the world. And it was basically because of that decision, to go to do that. So that’s one of the examples of Elon just really pushing— he always says we need to push to the limits of physics.
« Last Edit: 07/31/2018 05:17 pm by mme »
Space is not Highlander.  There can, and will, be more than one.

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