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Re: AO-40 squint angles (now and in the future).



Hi Doug,

The latest version of Instant-Track (v 1.50) handles the squint angle
issues you have raised.

At the moment, the attitude of AO-40 is given as 2.2,261.  If you enter
this into IT as +2.2,+81, then the blue arrow representing the axis of the
directional antennas, points the right way.  (The directional antennas on
AO-40 are on the same facet of the satellite as the 400N motor nozzle...
this needed to be pointing "backwards" so that energy could be added to the
orbit at perigee...  might have been a nasty outcome if it was facing the
other way!)

Now for utopia...  enter "L" for attitude.  This assumes that the
satellite's antennas always point straight into the centre of the earth.
Hopefully this is what we'll have when AO-40 is fully commissioned.  It's
what the UoSAT satellites do all of the time (except in rare cases, when
they get stood on their heads!).

Not sure about equivalent settings for other programs.

Regards,


Chris vk6kch



At 14:18 27/12/2000 -0500, you wrote:
>Hello,
>
>It was just pointed out to me that tracking programs which calculate
>squint angles for AO-13 will be off by 180 degrees for AO-40,
>since the directional antennas are on the "wrong" end of the satellite.
>Now I understand why I could hear the beacon this morning, but not
>this afternoon!
>
>But in the future, when AO-40 is 3-axis stabilized, how will the
>users deal with squint angle?  Will the satellite be stabilized
>so that it is always pointed exactly at the center of the earth?
>If so, tracking programs will need a different squint angle calculation
>algorithm (but not an especially complicated one).  But if AO-40
>needs to be off-pointed for one reason or another, how can the
>relevant attitude data be disseminated to users, and how will
>tracking programs use it?
>
>Doug
>NA1DB
>
>P.S.:  Somewhere in the last few days I saw a close-up photo of the
>S2 antenna. I can't remember if it was in QST, the Amsat Journal,
>or some Web page.  Anyone have any idea?  (It's the antenna with a row
>of holes in it.)
>
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