Author Topic: An SSME-related request  (Read 7868 times)

Offline Colds7ream

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An SSME-related request
« on: 01/16/2012 01:22 PM »
Hi folks,
   I've recently been doing some work on Wikipedia's article on the SSME, which you can find at http://en.wikipedia.org/wiki/Space_Shuttle_Main_Engine - I think its about done, but could really use an accuracy check to ensure I haven't misunderstood anything, so I'd appreciate it very much if someone who knows about SSMEs could wander over and take a look!

Cheers in advance!

Offline Wayne Hale

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Re: An SSME-related request
« Reply #1 on: 01/16/2012 02:14 PM »
Very nice article.  Lots of work obviously went into summarizing and extracting the existing information.  No significant errors that I detected but I would add a few clarifying points:
(1) The engine shutdown on STS-51-F that resulted in an abort to orbit was not caused by any performance problem with the engine but was rather was erroneously caused by failing redline sensors (temperature measurements).  The ATO action did not result in any loss of mission objectives or any shortening of mission duration.
(2) there were more pre-launch pad shutdowns that indicated in the article.
(3)  The final version of the SSME was ground tested up to 111% RPL with the intent to certify the use of 109% for intact (TAL, RTLS, ATO) abort modes.  However, vortex flow shedding on components in the main propulsion system plumbing (not the engines themselves) would have lead to low cycle fatigue failures at power levels above 104.5% so the higher power levels were never authorized for use in anything other than a contingency abort (where the failure to use them would have lead to LOCV).
(4)  To the end of the program, the engine start sequence incorporated two interesting features to limit acoustic/overpressure problems at the launch pad:  the engine starts were staggered by 120 msec, and the liftoff power level was 100% RPL; throttle up to 104.5% was accomplished immediately post liftoff.
(5)  The 104.5% power level (vs. 104.0%) was required for the upgraded Block II engines because of the loss of 2-ish seconds of ISP, this was not related to payload (although there was an early plan to use 106% power level for very heavy ISS elements, it was never required and would have incurred other problems - see 3 above).
(6) The lowest throttle down power level was increased to 67% for the same MPS fatigue problems discussed in 3 above.  The throttle bucket around Max Q was dynamically calculated based on early performance in first stage and generally resulted in throttle settings in the mid 70% range rather than automatically going to the minimum throttle setting of 67%. 

Probably a whole lot more detail than you need

Online Lee Jay

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Re: An SSME-related request
« Reply #2 on: 01/16/2012 02:25 PM »
0.5% thrust compensates for 2 seconds of ISP?  Maybe I'm not understanding.  Thanks for the info!

Offline Colds7ream

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Re: An SSME-related request
« Reply #3 on: 01/16/2012 02:48 PM »
Wow, a Shuttle-related article on Wikipedia actually being reviewed by a Shuttle program manager! Many, many thanks, Mr. Hale! I don't suppose I could persuade you to start a Wikipedia account too, by any chance? Goodness knows our Shuttle-related articles could do with a cleanup, and I can't think of a person better qualified! :-D I'll get to work on making those clarifications, thanks again for reviewing it!
(Lots of exclamation marks in that post, hmm... May be slightly over-excited...)
« Last Edit: 01/16/2012 04:09 PM by Colds7ream »

Offline kirghizstan

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Re: An SSME-related request
« Reply #4 on: 01/16/2012 03:17 PM »
Would recommend this change
"during" the "entirety"

Offline Colds7ream

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Re: An SSME-related request
« Reply #5 on: 01/16/2012 03:29 PM »
Made all those changes, what do people think?

Offline kevin-rf

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Re: An SSME-related request
« Reply #6 on: 01/16/2012 03:47 PM »
Made all those changes, what do people think?
I'm still picking my jaw off the ground from Wayne Hales response, there was an article? I also vote for drafting Wayne Hale to clean up Wikipedia!
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Offline mtakala24

Re: An SSME-related request
« Reply #7 on: 01/16/2012 03:53 PM »
There are still some grammar mistakes: "entered the orbiter at the an umbilical disconnect" -> "entered the orbiter at the umbilical disconnects" for one. Otherwise its quite good.
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Offline Colds7ream

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Re: An SSME-related request
« Reply #8 on: 01/16/2012 04:05 PM »
Made all those changes, what do people think?
I'm still picking my jaw off the ground from Wayne Hales response, there was an article? I also vote for drafting Wayne Hale to clean up Wikipedia!
I know, couldn't believe it! Best forum post response in history! ;D

Offline Colds7ream

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Re: An SSME-related request
« Reply #9 on: 01/16/2012 04:08 PM »
There are still some grammar mistakes: "entered the orbiter at the an umbilical disconnect" -> "entered the orbiter at the umbilical disconnects" for one. Otherwise its quite good.
Thanks - I've requested a good copyedit from Wikipedia's in-house Guild of Copyeditors, but any other errors you spot, do please let me know.

Offline DMeader

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Re: An SSME-related request
« Reply #10 on: 01/16/2012 05:01 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.
« Last Edit: 01/16/2012 05:06 PM by DMeader »

Offline Colds7ream

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Re: An SSME-related request
« Reply #11 on: 01/16/2012 05:29 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.

Fixed! Thanks! :)

Online Lee Jay

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Re: An SSME-related request
« Reply #12 on: 01/16/2012 06:36 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.

Fixed! Thanks! :)

Personally, I found it fascinating that breaching a fuel line resulted in a LOX ECO (rather than a fuel ECO), and why that happened.

Offline DavisSTS

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Re: An SSME-related request
« Reply #13 on: 01/16/2012 06:50 PM »
The full video and an amazingly technical overview thread for that STS-93 incident is on L2, but there's two samples of large relevance on the promo area, so both of these links work in here.

Click:
L2STS-93.wmv and STS-93L2VideoECOs.wmv.
 
On this thread link http://forum.nasaspaceflight.com/index.php?topic=9944.msg189521#msg189521
« Last Edit: 01/16/2012 06:50 PM by DavisSTS »

Offline strangequark

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Re: An SSME-related request
« Reply #14 on: 01/16/2012 06:55 PM »
This is possibly a nitpick, but the OMS link in the intro paragraph should use the yankee spelling of "Orbital Maneuvering System".
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Online MP99

Re: An SSME-related request
« Reply #15 on: 01/16/2012 07:51 PM »
I was going to submit a number of minor points, but have instead made the edit directly onto the page under userid MP99. This is the diff:-

http://en.wikipedia.org/w/index.php?title=Space_Shuttle_Main_Engine&action=historysubmit&diff=471743362&oldid=471719032

Pretty much grammer or style rather than actual detail changes, so marked as a "minor edit" (seemed to be appropriate according to wiki's help).

Happy for any of those to be reversed if you wish.

cheers, Martin

Online MP99

Re: An SSME-related request
« Reply #16 on: 01/16/2012 08:13 PM »
A few other items.

In my edit I changed a few entries from past to current tense. With SLS ISTM current tense is appropriate for RS-25 (unless referring to an older block), but past tense for Shuttle?

I've seen comments elsewhere that the early engines were known as RS-24, with block II earning the rename to RS-25, but I don't know whether that's accurate or not. However, for the sake of internal consistency it's worth noting that a search for RS-24 on wiki goes to http://en.wikipedia.org/wiki/RS-24 with a note "For the Space Shuttle engine, see Space Shuttle Main Engine." Presumably both can't be correct.

Gimbal angles are 10.5o according to http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-mps.html. Same page says max throttle 109%, so I think it applies to Block II.

"The engines are capable of throttling between 65% and 109% of their Rated Power Level in one percent increments". Raises the question how the engine throttles to 104.5%?

Re OMS assist on launches, I believe these weren't used on all launches. (This is one edit I did make).

"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").

cheers, Martin

Offline TJL

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Re: An SSME-related request
« Reply #17 on: 01/16/2012 08:20 PM »
If I remember correctly, the only missions that planned to use 109% thrust were STS 61-F and 61-G...both carrying the Centaur upper stage.

Online MP99

Re: An SSME-related request
« Reply #18 on: 01/16/2012 08:47 PM »
Another one.

Quote
The design for the SLS features the RS-25 on its core stage, with four different versions of the rocket - Block 0, I, IA & II - being installed with varying numbers of engines (3, 4, 4-5 & 5 respectively).

I'm sure block 0 is gone now, and Chris's latest article (reference #41) suggests either three or four RS-25 are being traded on block I. I wonder whether it would be safer to just say "between three and five engines".

cheers, Martin

Offline Colds7ream

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Re: An SSME-related request
« Reply #19 on: 01/16/2012 09:11 PM »
Thanks for all the help MP99, hope you'll decide to hang around Wikipedia awhile! :-) The edits you made were great, and I've changed the gimbal angle listed & the SLS cluster sizes; thanks for the reference. Regarding the RS-24, I asked around the Shuttle Q&A on this forum a while back, and the conclusion seemed to be that it refers to a different engine planned for use of the flyback booster during Phase A development.

Thanks for all the help folks, keep it coming if you spot anything else! I wish I could get help like this on-wiki!

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