[time-nuts] GRAIL USO

Jim Lux jimlux at earthlink.net
Sat Jun 1 20:03:10 EDT 2013


On 6/1/13 4:50 PM, Hal Murray wrote:
>
> jimlux at earthlink.net said:
>> It's also the knowledge of the process yield at each step which  means you
>> can stay in business.  APL knows how many to start at the  beginning to
>> insure they'll have 4 at the end, 2 years later.
>
> I assume there is a distribution.  Anything published on that?  How good are
> the next 4?
>

What's in Weaver's paper(s) is what's publically available.

As I recall, they had quite a few candidate oscillators to choose from 
that were going through long duration burnin.  There's a sort of complex 
process to pick the best of the litter.. do you want the one that shows 
the lowest drift rate, the one that's closest to the desired frequency, 
the one that has the lowest DC power, the highest RF output power, etc. 
    Turnover temperature is a critical thing, because it drives the DC 
power required to run the oven, and whether it can meet the mission 
requirements.

Low temp is good from a power standpoint (minimum heater power 
required), but bad from a "margins" standpoint: If it has to work at 
+70C, and the turnover temp is only +75, that's a challenge.  If the 
turnover temp is +100C, then you've got 30 degrees to work with, but 
you're going to draw a lot of heater power, esp when you're at the -55C 
test temp.



So the ones chosen for GRAIL were "best" by some criteria (e.g. best for 
the measurements GRAIL was making), but perhaps not "best" by some other 
criteria.

You can bet the "spares" at every step of the way aren't just thrown in 
the dumpster.  They wind up being used for future applications, 
sometimes because they're actually better for that than for GRAIL, or 
perhaps the application is willing to take what they can get.

I don't remember all the details (it was several years ago), but the 
burn in and test is of part of the system, and then they choose some to 
take the rest of the way and put into a package, etc.





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