Author Topic: An SSME-related request  (Read 37521 times)

Offline alexw

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Re: An SSME-related request
« Reply #20 on: 01/17/2012 05:32 am »
"Each engine would have to undergo a flight-readiness firing (FRF) before installation (the so-called "Main Engine Test" that NASA conducted with each new orbiter and prior to STS-26)." From a quick google, it looks like Shuttle FRF was with the engines mounted in the orbiter (ie not "before installation").
     Was each new-build engine from Rocketdyne not test-fired at Stennis before installation for first flight? (With the obligatory reconditioning/rebuild in between, of course.) But "FRF" might be reserved for the (6? 7?) done by the Orbiters themselves?
     -Alex

Offline Colds7ream

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Re: An SSME-related request
« Reply #21 on: 01/17/2012 06:16 am »
     Was each new-build engine from Rocketdyne not test-fired at Stennis before installation for first flight? (With the obligatory reconditioning/rebuild in between, of course.) But "FRF" might be reserved for the (6? 7?) done by the Orbiters themselves?
     -Alex
I swapped 'before installation' to 'before launch' - that better?  :)

Offline Skyjim

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Re: An SSME-related request
« Reply #22 on: 01/17/2012 06:25 am »
This is definitely a nit, but the nozzle and MCC were constructed differently - the description of brazed stainless steel tube wall is accurate for the nozzles, but the MCC used Narloy-Z copper alloy material and the cooling passages for the LH2 were machined slots in the Narloy-Z liner, electroplated over after machining with a copper layer jacketed by electrodeposited nickel, with the whole assembly then jacketed in a Inco 718 structural shell.

Spent 13 years doing chemical processing on SSME components at "The Rock".

A little outside my expertise, but regarding a question above, we used to discuss what we called "green runs" at Stennis for engines going into flight inventory, either new or overhauled.  FRFs were more  about integrated testing of the complete vehicle systems, propellant lines and valves, etc IIRC.  The SSMEs would already have been tested at SSC long before.

Jim
Ex-SSME builder, now doing public astronomy at Griffith observatory and a college planetarium.

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Re: An SSME-related request
« Reply #23 on: 01/17/2012 07:30 am »
     Was each new-build engine from Rocketdyne not test-fired at Stennis before installation for first flight? (With the obligatory reconditioning/rebuild in between, of course.) But "FRF" might be reserved for the (6? 7?) done by the Orbiters themselves?
     -Alex

I swapped 'before installation' to 'before launch' - that better?  :)

ISTM "before installation" is correct, but FRF is not. "Test firing at Stennis before installation"?

cheers, Martin

Offline Colds7ream

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Re: An SSME-related request
« Reply #24 on: 01/19/2012 01:19 pm »
This is definitely a nit, but the nozzle and MCC were constructed differently - the description of brazed stainless steel tube wall is accurate for the nozzles, but the MCC used Narloy-Z copper alloy material and the cooling passages for the LH2 were machined slots in the Narloy-Z liner, electroplated over after machining with a copper layer jacketed by electrodeposited nickel, with the whole assembly then jacketed in a Inco 718 structural shell.
Thanks! I made some changes to incorporate this information, what do you think?

Offline Wepush

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Re: An SSME-related request
« Reply #25 on: 01/19/2012 04:53 pm »
Personally, I found it fascinating that breaching a fuel line resulted in a LOX ECO (rather than a fuel ECO), and why that happened.

When there is a fuel leak, the engine recognizes that there is a drop in chamber pressure, and compensates by opening up the lox valve to return to commanded pressure.  So generally a fuel leak will cause the engine to run lox rich, and hot.  Also, there is always more propellant margins for fuel than for lox, because a lox rich cutoff is a bad day.

Offline Skyjim

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Re: An SSME-related request
« Reply #26 on: 01/19/2012 05:14 pm »
Quote
Thanks! I made some changes to incorporate this information, what do you think?

Looks good!


On lox-rich conditions, we used to refer to it as burning "hardware-rich".  Sobering to see the results of a lox-rich shutdown, with the interior of a powerhead, main injector, and pump turbine ends simply converted into a nasty dark gray slag...
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Offline kevin-rf

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Re: An SSME-related request
« Reply #27 on: 01/19/2012 05:48 pm »
When there is a fuel leak, the engine recognizes that there is a drop in chamber pressure, and compensates by opening up the lox valve to return to commanded pressure.  So generally a fuel leak will cause the engine to run lox rich, and hot.  Also, there is always more propellant margins for fuel than for lox, because a lox rich cutoff is a bad day.

Not following that logic of increasing the LOX mass flow. Is this due to limits on how much LH can be pushed into the SSME? But two points.

Even if the engine did not raise LOX pressure to compensate, a fuel leak will result a shift the burn towards a LOX rich.

Considering how low LH density is, there is less of a penalty for carrying extra LH. There is a significant penalty for carrying excess LOX.

Funny thing, the penalty is reversed for Kero/Lox rockets.
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Offline DMeader

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Re: An SSME-related request
« Reply #28 on: 01/19/2012 06:09 pm »
I was hoping that nozzle might have been one of those used for a RSSME. It would have been a nice bit of history.

Offline Wepush

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Re: An SSME-related request
« Reply #29 on: 01/19/2012 06:36 pm »
A few comments:
STS-55 occurred before STS-51, so you might want to swap the order in the list of failures.
I wouldn’t include the nozzle corrosion leakage as a failure.  It was a major reuse problem, but it didn’t impact the countdown or launch performance.  It was only discovered after landing.  There were many more significant technical issues than that one.
Fifteen flight plus two development engines at retirement don’t add up to “several dozen”.

The increased lox flow is because the engine uses the lox valve to control the chamber pressure, and the fuel valve to control the mixture ratio. 

Offline Colds7ream

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Re: An SSME-related request
« Reply #30 on: 01/22/2012 08:19 am »
Right - again, think I've made all relevant changes! :)

By the way, would anyone happen to know where I can find a NASA-made diagram of the throttle settings through launch (i.e. the thrust bucket) please?

Thanks.

Online AnalogMan

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Re: An SSME-related request
« Reply #31 on: 01/22/2012 12:50 pm »
By the way, would anyone happen to know where I can find a NASA-made diagram of the throttle settings through launch (i.e. the thrust bucket) please?

Is this the kind of thing you were looking for?

Original is page 13 of this document (105 pages 9.2MB):
http://www.lpre.de/p_and_w/SSME/SSME_PRESENTATION.pdf

Offline Colds7ream

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Re: An SSME-related request
« Reply #32 on: 01/22/2012 01:03 pm »
By the way, would anyone happen to know where I can find a NASA-made diagram of the throttle settings through launch (i.e. the thrust bucket) please?

Is this the kind of thing you were looking for?

That's the sort of thing, yes, but I can't use it due to licensing - it has to be a NASA-made diagram for me to upload it, as they're public domain.
« Last Edit: 01/22/2012 01:36 pm by Colds7ream »

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Re: An SSME-related request
« Reply #33 on: 01/22/2012 02:05 pm »
Would it be allowed on Wikipedia if you reproduced that diagram with matlab, excel or other tool and quoted the above as the source?

Offline Colds7ream

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Re: An SSME-related request
« Reply #34 on: 01/22/2012 02:29 pm »
Would it be allowed on Wikipedia if you reproduced that diagram with matlab, excel or other tool and quoted the above as the source?

It would, but I'm afraid I've no idea as to how I'd go about doing that! ???

Offline zeke01

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Re: An SSME-related request
« Reply #35 on: 01/23/2012 03:43 pm »
Quote
From the article...

"In addition, an oxidizer post, which had been intentionally plugged, came loose inside an engine's main injector and impacted the engine nozzle inner surface rupturing a hydrogen cooling line allowing a leak and resulting in a premature engine shutdown due to increased propellant consumption."

Actually, a 0.1" diameter, 1" long gold-plated pin, used to plug an oxidizer post orifice was what was ejected. The oxidizer post itself did not detach. Three nozzle cooling passages were breached.

Why was the plugging done in the first place?   Was this method a routine procedure to fix what, exactly?

Offline DMeader

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Re: An SSME-related request
« Reply #36 on: 01/23/2012 04:43 pm »
Quote
From the article...

"In addition, an oxidizer post, which had been intentionally plugged, came loose inside an engine's main injector and impacted the engine nozzle inner surface rupturing a hydrogen cooling line allowing a leak and resulting in a premature engine shutdown due to increased propellant consumption."

Actually, a 0.1" diameter, 1" long gold-plated pin, used to plug an oxidizer post orifice was what was ejected. The oxidizer post itself did not detach. Three nozzle cooling passages were breached.

Why was the plugging done in the first place?   Was this method a routine procedure to fix what, exactly?

Quoting Jenkins (3rd edition page 317)

Quote
"It had become common practice to deactivate main injector LO2 posts when they were determined to be life-limited because of manufacturing or operational damage. When a post life-limit was reached, a pin was inserted in the LO2 post supply orifice that shuts off the LO2 flow through the post, reducing high-cycle fatigue loading."

I would think that closing off some of the injector orifices might lead to bad things (combustion instability for instance) but apparently, it had become fairly common practice up until that point. I imagine there is probably more information on L2.
« Last Edit: 01/23/2012 04:43 pm by DMeader »

Offline Namechange User

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Re: An SSME-related request
« Reply #37 on: 01/23/2012 04:48 pm »
I would think that closing off some of the injector orifices might lead to bad things (combustion instability for instance) but apparently, it had become fairly common practice up until that point. I imagine there is probably more information on L2.

Combustion instability, etc was tested for.  However, one of these posts did become dislodged on STS-93 and punctured one of the regen jacket lines on the nozzle.
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Offline DMeader

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Re: An SSME-related request
« Reply #38 on: 01/23/2012 05:48 pm »
I would think that closing off some of the injector orifices might lead to bad things (combustion instability for instance) but apparently, it had become fairly common practice up until that point. I imagine there is probably more information on L2.

Combustion instability, etc was tested for.  However, one of these posts did become dislodged on STS-93 and punctured one of the regen jacket lines on the nozzle.

the SAIT Team report here http://history.nasa.gov/siat.pdf in the summary clearly refers to post pin ejection, not entire post. Not meaning to argue, but seems to me rather a significant difference.

Offline Wepush

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Re: An SSME-related request
« Reply #39 on: 02/03/2012 08:02 pm »
I got fairly confused with the description of the flow paths under "Components", particularly the lox.  I think "high pressure oxidizer preburner" is referring to the preburner pump?  And while it is split to the two turbines, it's probably relevant to note that it is partially burned in the preburners at that point.

What if you described the combustion stages, rather than just the propellant paths?  Such as... enter through the low pressure pumps... first stage of combustion in the preburners, fuel rich,... hot gas drives the high pressure pumps...second stage combustion in the main chamber.  Then add the tapoffs - e.g. warm lox from heat exchanger to pressurize pogo ball and repress tank.

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