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Re: What to do IF we regain control of AO-40

>The valve between the helium tanks and the hypergolic fuel tanks failed
>during ground testing and was repaired.  It was tested after returning
>from repairs and was found to work.  During the first attempt to start
>the 400N moter, the valve failed to open, so there was no fuel pressure
>and no burn occurred.  Once that was diagnosed, the ground controllers
>cycled the valve open and closed numerous times.  They did get it to
>open.  They did pressurize the fuel tanks.  The first burn did occur.
>To count up the successful and unsuccessful attempts at opening the
>helium pressurization valves, you would need to know how many times
>they were operated and failed to operate between the first and second
>attempt to light the 400N motor.  We don't know those counts.
> > Not encouraging.  Logic would then suggest that it has a 50/50 chance
> > of working the next time.  But since it failed on the ground then
> > worked after repair and then failed again we might assume that it may
> > have a 66 percent failure rate?
>Nope.  See above.  If the command team cycled the valves 10 times to
>get them unstuck, and they worked 9 times out of 10, then we get 3
>failures out of 12.  And this is simplistic, since the manufacturer
>might have tested the valve after repairing it with a hundred successful
>cycles, dropping the failure rate to 2 in 103 or some such figure.

NO, your logic is flawed. If the ground controllers had to make 10 attempts 
to open the valve when one (1) attempt would be the "norm" ... then the 
failure rate is 9/10 or 90 percent. If it had opened properly on the 1st 
attempt they would not have needed to make 9 more attempts to open it.


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