[Vwdiesel] Rabbit droppings --OT ----( The Discovery take off ? )

[Val Christian]

Claim to authority...we do allot of space systems at work, and fault tolerant
and "failsafe" designs are critical.  By their nature, they are not simple.
Hagar, you're not going to see the bent coathanger wire with a cork
on the bottom fuel gauge that you see on a Piper J-3 Cub.  Sorry.

I was chatting with the range safety officer at the Cape about this issue.
(He's the guy who gets to "push the button" if things go wrong on 
unmanned missions.)  Apparently the turbines that pump H2 and O2 to the 
engines are rather high power, and don't like being run "dry".  (75,000
hp my contact mentioned.  Just the fuel pump alone would really get my
Jetta going!).  

It's real easy to point to complex systems, and say they are "stupid".  
But frequently there are cost and performance tradeoffs which the designers
need to make.  For example, it's "stupid" to have an airliner grounded
when enough handheld flashlights are out of service as to not satisfy 
the minimum equipment list.  On the other hand, it would be stupider to 
actually have an emergency where those lights were needed, but none 
worked, and lives were lost.  

We all know that dumb things happen.  757s become gliders.  Vw diesels
run out of fuel on the road.  It's all where our tolerances are.  If my 
lawnmower runs out of gas, or even throws a rod, it's normally of small
consequence.  The same thing happening on my research aircraft, out over
a large body of cold cold water, with folks on board, and it's a very 
different situation.  It becomes more understandable when you participate
in the trade analysis.

Val



> 
>   Problem is the computer systems use those sensors to calculate burn times 
> and such.  More of a redundancy most likely as well as there being redundant 
> redundancies.  Kind of like complaining about two mags on your airplane 
> engine only you can't just coast in on your wings in the shuttle.  You need 
> fuel to control the angle of decent and the allowable angle is pretty small.  
> 
>   Can it be done without all of that?  Sure it can.  Is it as easy, foolproof 
> and 
> safe?  No way!  Seems like overkill but it IS outerspace and yes simpler 
> would be less problematic but not as precise (they only had a 10 minute 
> launch window).  
>   They have to make sure it goes flawlessly or the press will have a heyday!
>      Loren
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