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The auxiliary power unit is a hydrazine-fueled, turbine- driven power unit that generates mechanical shaft power to drive a hydraulic pump that produces pressure for the orbiter's hydraulic system. There are three separate APUs, three hydraulic pumps and three hydraulic systems.
REAL science threads deserve more attention and applause.
Yet, they (lke this one) attract little attention, when compared to the nonsense and Bravo Sierra types of threads that are becoming far too common, of late.
Sad, isn't it?
a thing that has 270,000 moving parts built by the lowest bidder? Makes you feel good doesn't it? Rockhound, Armageddon
Originally posted by weedwhacker
reply to post by LaTouffe
It is so very complicated, not only the machine, but all the parameters involved, each time to launch. Many factors to consider.
Launch scrubs all have a set minimum "turnaround time" I imagine (but, don't have the details handy) based on where they are, at any given point, within the count-down when the call to scrub is made.
So, the "48-hours" is like a default for them....a set window, where they can use the time to re-set everything needed to re-start the count-down, and meanwhile (hopefully) trouble-shoot and repair whatever was broken or inoperative.
But....the repairs may be more extensive than thought....so........delay, delay, delay. (It's much the same in the airline business, actually. But, not quite as complicated of course).
Each launch, too......has a different payload, with its unique needs and concerns...so that makes it more complex. Then, there is weather forecasts to worry about, and also the actual physical orbital mechanics, the "window of opportunity" for a launch, when the intent is to rendezvous with a moving target already on orbit, like the ISS.....so, you can see, there is a lot to consider.......
....of course, NASA has had a lot of practice!!