Delta 4-Heavy: success in doubt

[SpaceKiwi]

Just read the article on SDC confirming the fact that the Delta-4 Heavy's problem was propellant vaporization in the fuel line.<br /><br />I've got to ask what is this continued insistance in the space business of engine performance being rated at greater than 100%? Surely an engine develops a certain amount of thrust/speed/whatever with the 'throttle' opened right up, and that maximum developed 'grunt' should be identified as pedal-to-the-metal, goin'-like-the-clappers, flat-out-with-a-tail-wind 100% performance?!<br /><br />Also, with respect to the Delta problem, why the need to computer-control shut down the engines in a 'dry' situation? Wouldn't the dry line into the chamber make this redundant anyway? <div class="Discussion_UserSignature"> <p><em><font size="2" color="#ff0000">Who is this superhero?  Henry, the mild-mannered janitor ... could be!</font></em></p><p><em><font size="2">-------------------------------------------------------------------------------------------</font></em></p><p><font size="5">Bring Back The Black!</font></p> </div>

 

[henryhallam]

IIRC, with the SSMEs, they are rated at 104% thrust because they were upgraded from a previous version (which could produce 100% thrust max) and rather than change the scale, which could presumably impact trajectory calculations etc they just changed the upper limit to be "104%". Perhaps something similar occured during evolution of the Delta 4?<br /><br />And it does make sense to properly shut down the boosters when the tanks begin to run dry, otherwise unpredictable spurts of thrust could result as the 'dregs' get into the inlet. This is a bad thing for the flight computer which wants to know exactly how much thrust will be produced at a given time, to fine-tune the flight profile.

 

[drwayne]

There is also that time tested method of margin, or padding - in which you spec a part to a certain level, but you really know it is capable of, say, 1.25 times that number. For some applications, 1.5 is fairly routine.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

One thing that I was struck by. Some of the last telemetry from Challenger showed that computers were shutting down engines because of low pressure in the lines. The lady was doing the best she could, right up until the end.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>