[time-nuts] MTBF (was Rubidium standard)

[SAIDJACK at aol.com]

Hi Alan,
 
I am reading a book about the Apollo computer, they bet their life on it  
not failing (everything related to spacecraft maneuvering went through the  
computer, there were no mechanical or other backups whatsoever). They only 
had a  single computer per spacecraft!
 
The book states that based on the entire Apollo program, they later  
estimated the units MTBF to be in excess of 50,000 hours (which is actually not  a 
lot compared to what typical GPSDO's can achieve today).
 
A single transistor, ROM bit, solder-joint, or resistor failure could have  
killed them.
 
Scary considering they went for 2 week+ missions..
 
bye,
Said
 
 
 
 
In a message dated 11/18/2009 14:38:57 Pacific Standard Time,  
alan.melia at btinternet.com writes:

Sorry  Mike , unless, as someone else said, the figures are derived from
field  failures over at least a good porton of the expected like the MTBF
tells  you absolutely nothing!! The statistics used on the usual 1000hour
test  will only tell you the probability of failure in the first 1000hours  
of
use!! It cannot tell you anything mathematically about the  extrapolated
life....this has become another urban myth. If it works it is  more by luck
that by mathematical probability.

Alan  G3NYK