sjeyasin@phoebe.axion.bt.co.uk (swaraj jeyasingh) (04/28/89)
Reading the mail there appears to be several schools of thought on this: 1) it is 100 + x% increase on the design spec or nominal. Presumably this is due to improvements in the basic design. 2) it represents an operating thrust higher than what would be considered "peak efficiency" (with implications for saftey etc). Or as someone put it, "revving past the red line on the rpm counter" 3) To do with the fact that on gets "more thrust the higher one goes" My bet is with (1): Improvements on the original design requirment, which presumably was always known about, but only realised with time and experience. Similar to the way aircraft engines "grow" with time to give more thrust as engineering improvements are made. Then they are given a "new" name. e.g RB211-524 grew to be -535C which then became 535D which grew again to be -535E etc etc. (Don't qoute me on the exact marques for these) So what's the "consensus fidelium" and what is the RIGHT answer - anybody ? Swaraj Jeyasingh sjeyasingh@axion.bt.co.uk BTRL Ipswich IP5 7RE UK
labc-4da@web-1e.berkeley.edu (Bob Heiney) (04/30/89)
In article <1460@zaphod.axion.bt.co.uk> sjeyasin@axion.bt.co.uk writes: > > >Reading the mail there appears to be several schools of thought on this: > >1) it is 100 + x% increase on the design spec or nominal. >Presumably this is due to improvements in the basic design. > >2) it represents an operating thrust higher than what would be considered >"peak efficiency" (with implications for saftey etc). Or as someone put it, >"revving past the red line on the rpm counter" > >3) To do with the fact that on gets "more thrust the higher one goes" > I just read something about this, and what I believe is the correct reason is that the engines are rated to perform to some specification at a particular thrust. Thus the percentage is how much of the rated thrust you're using. Future missions are scheduled to go as high as 109% for heavy payloads (like the Hubble telescope). What *is* the rated thrust for the SRBs and the SSMEs? ------------------------------------------------------------------------------- | Bob Heiney "And in the end, the love you | | labc-4da@rosebud.Berkeley.edu take is equal to the love you make." | | -- The Beatles | -------------------------------------------------------------------------------
ricko@rosevax.Rosemount.COM (Rick O'Brien) (05/01/89)
In article <23778@agate.BERKELEY.EDU> labc-4da@web-1e.berkeley.edu (Bob Heiney) writes: >In article <1460@zaphod.axion.bt.co.uk> sjeyasin@axion.bt.co.uk writes: >>Reading the mail there appears to be several schools of thought on this: >> [stuff on various theories on thrust levels deleted] > >What *is* the rated thrust for the SRBs and the SSMEs? I design sensors that go on the SSMEs so while I am not an expert on the engines I have a *little* bit of info on what they do. As I understand it the 100% thrust level was the level the engines were first certified to. In order to go to 104% or higher every component has to go through a qualification program of test firings. The higher thrust levels are not strictly speaking the result of a new design (although design can be changed as a result of the testing) but rather the engine went through testing to certify that it could operate at 104% of the thrust that it was first certified to. I had heard that 109% will probably never but used after Challenger but 104% is used pretty much on all missions. I repeat, this is what I have been told by folks at Rocketdyne in casual conversation, I do not have access to mission data anymore. On the performance levels of the SSMEs I have this info: Type: Liquid Propellant, Pump-Fed, Regeneratively Cooled Propellants: Liquid Hydrogen/Liquid Oxygen Dimensions: 168 inches long/96 inches wide Mixture Ratio (o/f): 6.026:1 Thrust, Pounds Rated: 100% 104% 109% Sea level 375,000 393,000 417,300 Vacuum 470,000 488,800 512,300 Pressures,psia Hydrogen Pump Discharge 6,140 6,445 7,040 Oxygen Pump Discharge 7,075 7,380 8,070 Combustion Pressure 3,006 3,126 3,260 Flowrates,lb/sec(gpm) Total 1,040(20,737) 1,081(21,570) 1,133(22,568) Hydrogen 148(15,098) 154(15,710) 161(16,424) Oxygen 892( 5,639) 927( 5,860) 972( 6,144) Power, Horsepower (High Pressure Pumps) Hydrogen 63,200 69,100 77,310 Oxygen 21,300 23,600 29,430 rick o'brien