[time-nuts] MTBF (was Rubidium standard)

[SAIDJACK at aol.com]

Hi Poul-Henning,
 
from what I read, they a) had no tools to replace the units or  even open 
the computer, b) the software was different between the units  (LEM had 1/2 
the ROM to save weight), and c) the spacecraft attitude thrusters  and the 
main engines were fully computer controlled (their control  Joysticks were 
true fly-by-wire, they went through the computer, and thruster  control was 
done by software). So no computer meant no attitude thrusters  or acceleration.

So having to rely on two of these computers during the separated period  
would actually double their chances of some form of mission failure. Of course 
 the LEM could not be used for re-entry in to the atmosphere either.
 
If the Command Module computer failed (and it was apparently not built with 
 redundant circuitry) then: - game over.
 
But on the other hand they considered the human element failure, they had  
fully automatic return and landing capability in case the humans  expired...
 
bye,
Said
 
 
 
 
In a message dated 11/18/2009 15:07:02 Pacific Standard Time,  
phk at phk.freebsd.dk writes:

In  message <cb8.5c4f5c26.3835d6b2 at aol.com>, SAIDJACK at aol.com  writes:

>A single transistor, ROM bit, solder-joint, or resistor  failure could 
have  
>killed them.

Actually there were a  perfectly good spare in the lunar lander module
and most single points of  failure would not kill them, but merely
cause the mission to abort and head  home.

They also hard backup navigational  aids.