On 6/1/13 8:49 AM, Attila Kinali wrote:
On Tue, 28 May 2013 20:23:06 -0700
Jim Lux <[email protected]> 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.
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