Author Topic: SpaceX: Merlin 1D Updates and Discussion Thread 2  (Read 352939 times)

Offline guckyfan

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #500 on: 01/08/2016 04:41 PM »
What has to be different between center and outside engines is not throttle, but gimbal.

Not necessarily. Different available space for gimbal does not translate into different hardware, just software restrictions on its use.

Online Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #501 on: 01/08/2016 04:54 PM »
What has to be different between center and outside engines is not throttle, but gimbal.

No, they all gimbal. See this image, which highlights the gimbal actuators for the outer engines:

Online cambrianera

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #502 on: 01/08/2016 05:02 PM »
I said “gimbal has to be different“
I did not say “hardware for gimbal has to be different“
I did not say “no gimbal“

Edited and rephrased
« Last Edit: 01/08/2016 05:33 PM by cambrianera »
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Online Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #503 on: 01/08/2016 05:05 PM »
Gimbal has to be different.
(What is so difficult to understand in this?)

Hint: not hardware for gimbal has to be different; not no gimbal.

Gimbal limits, yes, but that might only be a software limit for the outer engines. And instead of hinting, say what you mean. (w/ source)
« Last Edit: 01/08/2016 05:23 PM by Lars-J »

Online Chris Bergin

Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #504 on: 01/08/2016 05:15 PM »
Gentlemen, please! Be civil.
« Last Edit: 01/08/2016 05:15 PM by Chris Bergin »

Online cambrianera

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #505 on: 01/08/2016 05:24 PM »
Gimbal should be limited:
-by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
-by hardware, stroke limiting clamps are visible on actuators of outboard engines.
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Offline JamesH

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #506 on: 01/08/2016 05:28 PM »
Gimbal should be limited:
-by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
-by hardware, stroke limiting clamps are visible on actuators of outboard engines.

Doesn't make the engine 'different' surely? Just a different mount. All engines are still coming off the same production line.

Offline Kabloona

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #507 on: 01/08/2016 05:34 PM »
stroke limiting clamps are visible on actuators of outboard engines.

Those appear to be electrical harness clamps, not mechanical stops, which are typically internal to TVC actuators and not externally visible.

Anyway, drifting off topic. The point is, there's no reason to doubt the statement that all F9 first stage engines are identical. The differences being discussed above (throttling, gimbal angle input limits) are all *external* to the engine itself.
« Last Edit: 01/08/2016 05:38 PM by Kabloona »

Online MechE31

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #508 on: 01/08/2016 05:48 PM »
stroke limiting clamps are visible on actuators of outboard engines.

Those appear to be electrical harness clamps, not mechanical stops, which are typically internal to TVC actuators and not externally visible.

Anyway, drifting off topic. The point is, there's no reason to doubt the statement that all F9 first stage engines are identical. The differences being discussed above (throttling, gimbal angle input limits) are all *external* to the engine itself.

They could also be ground handling stops to prevent unintended movement of the engines.

Offline ArbitraryConstant

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #509 on: 01/08/2016 06:26 PM »
That still doesn't answer whether it's ONLY the center engine that throttles
I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.

Offline guckyfan

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #510 on: 01/08/2016 09:24 PM »
That still doesn't answer whether it's ONLY the center engine that throttles
I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.

Can we assume then that the center engine throttles more than the others?

Offline Fluke72

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #511 on: 01/08/2016 09:35 PM »
Gimbal should be limited:
-by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
-by hardware, stroke limiting clamps are visible on actuators of outboard engines.

those "limiting clamps" are temp installed to prevent movement of TVC actuators until flight and during shipping (or during testing).
former SpaceX technician

Offline Silmfeanor

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #512 on: 01/08/2016 09:40 PM »
That still doesn't answer whether it's ONLY the center engine that throttles
I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.

Can we assume then that the center engine throttles more than the others?
They all are able to throttle; I assume the center one is more precise or has a faster response due to the added biprop valve, and gives faster feedback about the actual performance due to added instrumentation. This does not necessarily change anything about the engine structure itself, but is more like an added package only installed for the center engine.

Or atleast, this seems to me to combine both having just 1 type of M1D and there being some additions to the throttling of the center engine.

Offline baldusi

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #513 on: 01/10/2016 10:48 AM »
Normal way of throttling could be limiting the fuel or oxidizer flow to the TP. I think many gas generators do this. If this is how the Merlin 1D does it, it would always keep a fixed O/F ratio.
The issue might be that you have an oxidizer that evaporates. And thus, if you can adjust the O/F you can make better use of the propellant reserves.
Centaur and DIVUS do this regularly to optimize propellant usage. I could bet that the Vac version of the Merlin 1D does it to optimize for different mission profiles (a GTO transfer would have LOX boiloff).
This valve might be the reason Merlin 1D Vac does 100% to 39% (data from F9 User Guide v2.0). It might also enable the center engine to also achieve better throttling capabilities. Albeit the core engine might be limited by the instabilities generated from an over-expanded nozzle.

Online dkovacic

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #514 on: 01/18/2016 01:44 AM »
Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

Online Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #515 on: 01/18/2016 02:29 AM »
Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

There are several differences, you cannot do this. The geometry of the nozzle (before nozzle extension) is very different, and on the vacuum model the turbopump exhaust is gimballed with the engine nozzle and injected into the nozzle. The M1DVac also has more thrust than the M1D.

This is not M1D, but here is a picture showing the M1C (center) and M1C-Vac (right) - That should show you that there is MUCH more difference between these kinds of engines beside a nozzle extension.
« Last Edit: 01/18/2016 02:29 AM by Lars-J »

Offline Saabstory88

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #516 on: 01/18/2016 02:31 AM »
Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

The thrust chamber / nozzle interface does not appear to be identical.

http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

http://www.spacex.com/files/assets/img/merlinvac.jpg

Offline Llian Rhydderch

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #517 on: 01/18/2016 08:21 PM »
Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

The thrust chamber / nozzle interface does not appear to be identical.

http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

http://www.spacex.com/files/assets/img/merlinvac.jpg

Yes, those two photographs are very helpful in showing for the Merlin 1D and Merlin 1Dvac the same sorts of differences that were shown above in the excellent post by Lars-J.

Perhaps one of you, or another image-savvy editor, could make a side-by-side single image of those two, so that Lars-J's point could be well illustrated with the 1D technology.
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Online Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #518 on: 01/18/2016 11:15 PM »
Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

The thrust chamber / nozzle interface does not appear to be identical.

http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

http://www.spacex.com/files/assets/img/merlinvac.jpg

Yes, those two photographs are very helpful in showing for the Merlin 1D and Merlin 1Dvac the same sorts of differences that were shown above in the excellent post by Lars-J.

Perhaps one of you, or another image-savvy editor, could make a side-by-side single image of those two, so that Lars-J's point could be well illustrated with the 1D technology.

Here's the best I could do. The angles are different, but I tried to size them such that the combustion chamber is the same size.

Offline Saabstory88

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #519 on: 01/19/2016 12:03 AM »
Notice where the high pressure line from the RP-1 turbopump interfaces with the chamber wall. Those are likely the same distance on both engines. MVac even seems to have additional fuel cooled walls lower than this interface.

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