[time-nuts] GRAIL USO

[Jim Lux]

On 6/1/13 8:49 AM, Attila Kinali wrote:
> On Tue, 28 May 2013 20:23:06 -0700
> Jim Lux <jimlux at earthlink.net> wrote:
>
>> The USO's we got for GRAIL from APL have ADEV<1E-13 from 1 to 1000
>> seconds, and then heads up at 1 decade/decade.  The lowest ADEV is about
>> 5E-14 at around 50 seconds, but it's pretty flat.  See the paper by
>> Enzer et al.
>
> Do you mean [1]?
>
> [1] "GRAIL ­ A Microwave Ranging Instrument To Map Out The Lunar Gravity Field",
> by Enzer, Wang, Klipstein, 2010
>

Yes...

>
>> Or better, the 42ns PTTI conference paper by Greg Weaver at APL, who had
>> to build them.
>
> That would be [2] then? A little question here: AFAIK satelites vibrate
> a lot. How do they account/compensate for the vibrations in the oscillators?

yes..

Significant vibration is only during launch. And during pyro events for 
deployments, of course.  After you're in orbit, the vibration is very, 
very small (bearing noise from the reaction wheels) . I doubt they're 
making measurements while they use the thrusters.  If they're changing 
the orientation, it's probably using wheels.  And wheel bearing noise is 
probably fairly narrow band and harmonically related to the wheel speed. 
  I can ask some GRAIL-ers.


>
> [2] "The Performance of Ultra-Stable Oscillators for the Gravity Recovery and
> Interior Laboratory (GRAIL)", by Weaver, Garsecki, Reynolds
> http://www.pttimeeting.org/archivemeetings/2010papers/paper28.pdf
>
>
>> They run in a vacuum bottle (of course), and they have somewhat
>> obsessive attention to a lot of details.  But I suspect that aside from
>> the space qual aspects, the whole "how you build them" isn't a whole lot
>> different.
>
> Is any of the design documents for those crystal oscillators available?
> I would be very much interested to have a look at them.


Not a chance <grin>
a) they are JHU/APL proprietary
b) they are export controlled

What's in Weaver's papers over the years is what you're going to see, 
for the most part.

The actual resonator and oscillator and packaging hasn't changed a whole 
lot from the Transit days, apparently. Particularly for the packaging, 
it's very much an art and craft to get the mechanical stresses low, and 
I've heard the folks who learned to do it as a young'un for Transit in 
1960 at Bliley are still doing it today.  I would hope they have young 
apprentices (who are probably in their 40s and 50s).

I would imagine that Oscilloquartz is pretty much the same.  The basic 
physics is published and moderately well known. Producing very high 
quality is mostly a matter of being very, very careful at each step of 
the way, and starting with a lot, so that at the end of the process, you 
have just a few good ones.  The "secret sauce" for the companies 
involved is things like knowing how to set up the tests, fixturing, 
which parts from which manufacturer seem to work the best and all that 
stuff.  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. 
Overestimating yield means you wind up at delivery time without the 
product in hand. Underestimating means the price gets high, and your 
customers might start contemplating system designs that don't need your 
product.  Science satellites, oddly enough, are remarkably price 
sensitive, even though they are building one of a kind units at $1M each.