[amsat-bb] Re: Re: Re: Re: AO40 Hiatus / sunangle

["Stacey E. Mills" <w4sm@xxxxxxxxxx>]

>The 11/5 message mentioned the offpointing, which did not surprise me
>when I read it at the time.
>
>But the ARRL article was the very first place I heard that the transponders
>would be shut down for the duration.  This surprised me, since I assumed
>that the offpointing could be done by changing only the ALON and leaving
>the ALAT close to zero, so that the transponder could be operated for a
>brief but usable period during each orbit when the squint angle would
>be small enough.

The sun has to "pass" us.  We can't simply change ALON unless we want to 
chase the sun all around the ALON circle, which would take us a year 
(almost) to get back to 0/0 and would force us to pass through 180/0 with 
really horrible signals for several months.  In order to maintain solar 
power and sensors when the sun passes, we have to raise or lower 
ALAT.   Since the sun is now low on the ecliptic and is passing the back 
(omni) side, it is easier to lower ALAT to maintain acceptable solar 
angles.  ALON will also be adjusted to minimize the ALAT change and 
maximize our sensors....  Users of AO-13 will well remember similar 
times.  With AO-13, we went to the omni antennas during these times.  With 
AO-40, we have no omnis......  During these times, the passbands will be on 
if the squint is reasonable, but  there is no reason to have them active if 
the squint is prohibitive.   I had hoped to outline all of this in an 
update for the amsat-bb last week, but my day job and the actual planning 
of  the events has kept me too busy.  When we start the move, we'll outline 
the plan and time line.

>BTW, the article also said:
>
> >The satellite is currently in a long period during which Earth
> >eclipses the sun near perigee--its point closest to Earth. AO-40
> >relies on solar panels for its power.
>
>The the perigee eclipse actually have a significant effect on
>the power budget? I thought this eclipse only lasted for about
>10% of the orbit.

The perigee eclipses will continue for many months but don't last very 
long.  Therefore,  don't really affect the power budget, but they do affect 
magnetorquing because without the sun, the sensors can't  "despin" the 
magnetoquers.  So torquing is not as efficient, particularly when the 
eclipse is right at perigee.



-- 
  _______________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
  _______________________________________________________________________

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org