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RE: UO-22 news



Gravity gradient stabilisation only provides very course pointing - say, 30
or 40 degrees - it depends on the satellite.

We use magnetometers to control the attitude of the satellite to within 1
degree, and spin it at 0.6 deg/s (10 minute spin rate).

To turn the satellite over, we fire the torquers to increase the libration
until finally flips over when we fire to reduce the libration.  This takes a
long time to build up the libration to the point that it goes over the top.
In the case of UO-22, it took about 24 hours to complete the move.

Chris

-----Original Message-----
From: Mark Johns [mailto:mjohns@cfu.net]
Sent: 19 January 2000 23:11
To: Chris Jackson
Cc: 'amsat-bb@amsat.org'
Subject: Re: [amsat-bb] UO-22 news


Chris Jackson wrote:

> UO-22 has now entered full sunlight and the temperatures have increased
> considerably.  I have turned the satellite upside down to point the
critical
> systems to cold space - a maneuver which takes a couple of days due to the
> gravity gradient boom. . . .

My turn to ask a "stupid" question:   How does one turn a satellite with a
gravity gradient boom "upside down?"  I thought the boom was a passive
stabilization device that kept the boom pointed toward earth at all times.
What
does UO-22 have aboard that counters this, and what keeps the boom from
promptly
swinging earthward once again?
--
Mark D. Johns, Cedar Falls, Iowa -- K0MDJ (EN32sm)
              http://pages.cfu.net/~mjohns/index.html
 "Heaven goes by favour.  If it went by merit, you would
    stay out and your dog would go in." -- Mark Twain


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