Author Topic: SpaceX: Merlin 1D thread  (Read 520314 times)

Offline Davidthefat

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Re: SpaceX: Merlin 1D thread
« Reply #760 on: 07/29/2013 11:50 pm »
I'm surprised that this picture has not been posted here; http://imgur.com/XvAI5rR

The reason why the fuel line is bent in is to allow for more space when the engine is gimballed. AFAIK, this is pretty much the completed engines ready to be mounted on the octagon shaped structure in the back; I think only the fuel and oxidizer lines and wires have to be installed to interface with the main fuel tanks. The turbopump assembly seems to be missing the exhaust pipe and the hydraulic actuators.

The first one on the foreground is the most complete...u can see the exhaust manifold/pipe to the side of the combustion chamber..

The pipe that extends from that is missing. What you are seeing is the turbopump assembly; yes, the exhaust manifold that's downstream from the turbine is there, but not the actual pipe. The actual pipe converges slightly to form a nozzle at the tip.


edit: unless they shortened it dramatically.

Well, I'll be... It does seem they have shortened it significantly from the last revision.


Can compare it with the 1C in the picture below...quite shorter..overall I think more compact and smaller..

http://www.popularmechanics.com/cm/popularmechanics/images/WZ/spacex-factory-06-0112-lgn-87860333.jpg

This picture shows the M1Ds ready for static testing, with its shorter exhaust. http://i.imgur.com/lj9zTrL.jpg

Offline justineet

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Re: SpaceX: Merlin 1D thread
« Reply #761 on: 07/30/2013 01:05 am »
I'm surprised that this picture has not been posted here; http://imgur.com/XvAI5rR

The reason why the fuel line is bent in is to allow for more space when the engine is gimballed. AFAIK, this is pretty much the completed engines ready to be mounted on the octagon shaped structure in the back; I think only the fuel and oxidizer lines and wires have to be installed to interface with the main fuel tanks. The turbopump assembly seems to be missing the exhaust pipe and the hydraulic actuators.

The first one on the foreground is the most complete...u can see the exhaust manifold/pipe to the side of the combustion chamber..

The pipe that extends from that is missing. What you are seeing is the turbopump assembly; yes, the exhaust manifold that's downstream from the turbine is there, but not the actual pipe. The actual pipe converges slightly to form a nozzle at the tip.


edit: unless they shortened it dramatically.

Well, I'll be... It does seem they have shortened it significantly from the last revision.


Can compare it with the 1C in the picture below...quite shorter..overall I think more compact and smaller..

http://www.popularmechanics.com/cm/popularmechanics/images/WZ/spacex-factory-06-0112-lgn-87860333.jpg

This picture shows the M1Ds ready for static testing, with its shorter exhaust. http://i.imgur.com/lj9zTrL.jpg

Yes there are some significant changes in terms of form. The combustion chamber seems also to be different from the 1C. The 1C has a funnel shape while the 1D looks like a small barrel...kinda of a small beer keg..

Offline GalacticIntruder

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Re: SpaceX: Merlin 1D thread
« Reply #762 on: 07/30/2013 09:16 pm »
Is the M1D Vac really 801kN? That is a big boost, more than I was expecting anyway. No ISP mentioned though.

Or, is it marketing hype?
« Last Edit: 07/30/2013 09:16 pm by GalacticIntruder »
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Offline ugordan

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Re: SpaceX: Merlin 1D thread
« Reply #763 on: 07/30/2013 09:28 pm »
Same chamber and mass flow rate as the sea-level Merlin 1D and a nozzle optimized for vacuum. Higher Isp and higher thrust are directly related here.

Offline sublimemarsupial

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Re: SpaceX: Merlin 1D thread
« Reply #764 on: 07/30/2013 09:31 pm »
From the new spaceX website "SpaceX's Merlin vacuum engine has the highest vaccum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vaccum isp of 340 seconds"

Offline PreferToLurk

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Re: SpaceX: Merlin 1D thread
« Reply #765 on: 07/30/2013 09:54 pm »
From the new spaceX website "SpaceX's Merlin vacuum engine has the highest vaccum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vaccum isp of 340 seconds"

Interesting, wikipedia, sourcing a spacex press release, claims the M1c Vac had an ISP of 342 seconds. But of course the link is now dead with the site redesign...

So did the old engine really out-ISP the new engine?  It obviously delivers a lot more thrust, but it seems odd that they would trade ISP away for the second stage engine.

Offline pippin

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Re: SpaceX: Merlin 1D thread
« Reply #766 on: 07/30/2013 09:57 pm »
It might use a shorter nozzle, they had to redesign that, didn't they?
Or the 342s was the original wishful-thinking figure
« Last Edit: 07/30/2013 09:58 pm by pippin »

Offline ugordan

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Re: SpaceX: Merlin 1D thread
« Reply #767 on: 07/30/2013 10:06 pm »
Interesting, wikipedia, sourcing a spacex press release, claims the M1c Vac had an ISP of 342 seconds.

COTS-C1 press kit said M1c-Vac had 336 s Isp, IIRC.

Offline Arthree

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Re: SpaceX: Merlin 1D thread
« Reply #768 on: 07/31/2013 04:43 am »
801 kN with the same mass flow rate as M1D would imply ~346s, which I believe was the number floating around previously.

(801 kN/716 kN)*311 s = 348 s
(801 kN/654 kN)*282 s = 345 s

Offline malu5531

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Re: SpaceX: Merlin 1D thread
« Reply #769 on: 08/21/2013 07:29 pm »
(801 kN/716 kN)*311 s = 348 s
(801 kN/654 kN)*282 s = 345 s

I believe the vac thrust of Merlin 1D is ~741 kN, from spacex.com; 1500000 lbf / 9 ~ 166.5 klbf ~ 741 kN.

Instead of 311s for Vac ISP for Merlin 1D (non Vac), we use 320;
Merlin 1D Vac ISP: 1500000/1323000 * 282 = 319.73 (total Vac/SL thrust, from spacex.com)

This would also make the calculation match better;
(801 kN/741 kN)*319.73 s = 345.6 s
(801 kN/654 kN)*282 s = 345.4 s

Difference probably due to rounding.
« Last Edit: 08/21/2013 07:31 pm by malu5531 »

Offline Arthree

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Re: SpaceX: Merlin 1D thread
« Reply #770 on: 08/22/2013 03:00 am »
(801 kN/716 kN)*311 s = 348 s
(801 kN/654 kN)*282 s = 345 s

I believe the vac thrust of Merlin 1D is ~741 kN, from spacex.com; 1500000 lbf / 9 ~ 166.5 klbf ~ 741 kN.

Instead of 311s for Vac ISP for Merlin 1D (non Vac), we use 320;
Merlin 1D Vac ISP: 1500000/1323000 * 282 = 319.73 (total Vac/SL thrust, from spacex.com)

This would also make the calculation match better;
(801 kN/741 kN)*319.73 s = 345.6 s
(801 kN/654 kN)*282 s = 345.4 s

Difference probably due to rounding.

There are varying figures for the performance of M1D.  Before the page was updated, it listed the vacuum Isp as 311s and thrust as 161000 lbs (720kN).  The Falcon Heavy M1D page on spacex.com lists it now as having 309s and 161000 lbs (716kN), and the F9 version confirms it (without a mention of Isp).

320s seems exceptionally high, far above what it was predicted to have (310s) when it was designed, and the SL Isp doesn't seem to have changed.  I would guess that the numbers posted on the F9/FH pages (1,500,000 lbs/6672 kN per core) are either rounding errors or wishful thinking on SpaceX's part.

Or they somehow managed 9 more seconds of vacuum Isp without affecting SL performance.

Offline IRobot

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Re: SpaceX: Merlin 1D thread
« Reply #771 on: 08/22/2013 07:21 am »
Doesn't it depend on the stage? AFAIK, the 2nd stage Merlin 1D is optimized for vacuum, with larger nozzle.

Offline aga

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Re: SpaceX: Merlin 1D thread
« Reply #772 on: 08/22/2013 08:46 am »
the 2nd stage merlin is optimized for vacuum and its isp = 340 s
source: http://www.spacex.com/falcon9 - you can see the info, when you click the "inside the interstage" blue text
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Offline malu5531

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Re: SpaceX: Merlin 1D thread
« Reply #773 on: 08/22/2013 09:25 am »
I would guess that the numbers posted on the F9/FH pages (1,500,000 lbs/6672 kN per core) are either rounding errors or wishful thinking on SpaceX's part.

Or they somehow managed 9 more seconds of vacuum Isp without affecting SL performance.

OR the mass flow rate is not the same; another explanation could be that they run the engines at lower throttle near SL, and then throttle up in vacuum (after MaxQ). However, I can't see why you would throttle down early during launch - during MaxQ, yes, but the initial flight?

I agree with the rounding; 282/311 Isp & 1323 klbf SL thrust, means Vac thrust is 1459 klbf, which would not be totally unreasonable to round to 1500 klbf for marketing purposes. However, then we would have an inconsistency with the 801 kN Merlin 1DVac thrust (assuming equal mass flow - full throttle).

Doesn't it depend on the stage? AFAIK, the 2nd stage Merlin 1D is optimized for vacuum, with larger nozzle.

If thrust is increased from 147 klbf (Merlin 1D SL) to 180 klbf (Merlin 1DVac), by means of less ambient atmosphere, nozzle extension, etc, while keeping the same fuel and fuel-flow; the Isp ratio will be the same as thrust ratio, in this case 180/147 = 1.224, which means Isp for Merlin 1DVac would be 345.3.

the 2nd stage merlin is optimized for vacuum and its isp = 340 s
source: http://www.spacex.com/falcon9 - you can see the info, when you click the "inside the interstage" blue text

There is inconsistencies in the information, yes. If we assume the 340s number is correct (which some say would be lower than the Merlin 1C, hence unreliable), the 1DVac thrust should be 177 klbf, which in itself is not unreasonable to round to 180 klbf.

(personally, I don't believe in the "wishful thinking" hypothesis)

Offline Arthree

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Re: SpaceX: Merlin 1D thread
« Reply #774 on: 08/22/2013 03:53 pm »
Quote
If we assume the 340s number is correct (which some say would be lower than the Merlin 1C, hence unreliable), the 1DVac thrust should be 177 klbf, which in itself is not unreasonable to round to 180 klbf.

Good point -- 177000 lbs is more in line with Elon's "80 tons" statement, and 340s might be reasonable if the vacuum nozzle is actually shortened to fit into a smaller interstage.

Offline Chris Bergin

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