Jim - 4/3/2006 6:12 PMMany threads have asked the question: How can you have more than 100% thrust (much like the Spinal Tap volume setting of 11)? The SSME was designed to provide a thrust of 375,000 pounds at sea level. This is the rate power level. It is similar to how jet engines are rated. This means that there are design margins that allow the engine to operate at this level and still maintain safety limits, temp limits, design life, reusability, etc. 0nce the SSME was designed and tested it was found that there was excess margins and this meant that the engine could be operated at a higher power level and still maintain safe margins. 104 % was the first increment and has been used for every mission since it was approved (STS-X). 109% is another story.
Launch Fan - 4/3/2006 7:10 PMYou guys might be able to help with this:http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=656&start=1Video and audio feed from inside the flight deck on launch. Maybe the comments on that particular launch could go on that thread - while this continues on the actual SSME throttle settings.
mkirk - 4/3/2006 7:15 PMQuoteLaunch Fan - 4/3/2006 7:10 PMYou guys might be able to help with this:http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=656&start=1Video and audio feed from inside the flight deck on launch. Maybe the comments on that particular launch could go on that thread - while this continues on the actual SSME throttle settings.Actually I had planned to post a "quasi-transcript" of a typical launch on this web site. While I may or may not be able to decipher the poor audio on that video I can tell you exactly what is supposed to be said and by whom as this is standardized. The internal call outs are standard but some crews will make subtle changes and of course they will also make remarks and comments to each other that are not part of the call outs.I promise to do this soon.Mark Kirkman
lmike - 4/3/2006 7:15 PMThanks for this thread. I've been curioius about this. How is the 'extra throttle' implemeted physically? Is it simply more propelants (per unit time) injected into the chamber, higher turbopump speeds, ...? Or is there 'extra' hardware to implement the 100+% throttle? Or is the engine hardware basically the same prior to 100% and after they found they could go beyond? Does the physical throttle 'lever' have more settings, or just the lever step size re-calibrated to signify larger increases in output (to the engines) Sorry for naive questions.
Rob in KC - 4/3/2006 7:22 PMI've seen many a school teacher wince in pain when George Diller mentions "All three engines back at 104 percent of rated performance"
Rob in KC - 4/3/2006 9:12 PMI was being humorous Ben!
lmike - 4/3/2006 8:19 PMThank you very much for the explanation and the link! This answers my questions. The preburner valves!