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AO-40 Attitude Information




Dear All,

May I take this chance to say a big thank you to our command stations
James Miller G3RUH, Stacey Mills W4SM, Ian Ashley ZL1AOX, Graham 
Ratcliff VK5AGR, and all those who support them with telemetry, for 
an outstanding effort in keeping AO-40 operational and work as it's best.
Special thanks also to Paul Willmott for keeping the telemetry archive
up to date and organizing all the mass of telemetry data.

HAPPY NEW YEAR to everyone!!

best wishes
 Peter 

--
 Peter Guelzow, DB2OS
 Pres. AMSAT-DL



The following information is provided by G3RUH:

______________________________________________________________________________

AO-40 Attitude Information
--------------------------
The YACE camera was activated on Orbit 535 in order to check the AO-40
attitude.

This is done every 5 orbits which also enables calibration of the excess
precession in ALON (the so-called "Mystery Effect").

Presently the Sun sensors cannot see the Sun, so the Sun/Earth sensor system
is unuseable.  This "hibernation" commenced on orbit 529 (Dec 24) and will
continue until orbit 549 on 2002 Jan 09 [Wed].  You can tell that this is the
case because the telemetered analogue spin rate is meaningless;  the true
spin rate is in fact 2.51 rpm.

   Today Dec 29 on orbit 535 the attitude measured  ALON 327.4, ALAT -11.4
                 with an uncertainty of order 0.1 deg.

The attitude direction will drift as follows:

                                      Sun  Illumin-
DATE                  ALON   ALAT    Angle  ation %
---------------------------------------------------
2001 Dec 20 [Thu]    347.5  -10.2    -37.2   79.7  
2001 Dec 21 [Fri]    345.7  -10.2    -39.0   77.7  
2001 Dec 22 [Sat]    342.2  -10.2    -41.8   74.5  
2001 Dec 23 [Sun]    340.3  -10.3    -43.5   72.5  
2001 Dec 24 [Mon]    338.5  -10.3    -45.1   70.6  << Sun sensor stopped 
2001 Dec 25 [Tue]    336.6  -10.3    -46.5   68.8      ..    ..     ..
2001 Dec 26 [Wed]    333.1  -10.3    -48.6   66.2      ..    ..     ..
2001 Dec 27 [Thu]    331.3  -10.3    -49.7   64.7      ..    ..     ..
2001 Dec 28 [Fri]    329.5  -10.4    -50.7   63.4      ..    ..     ..
2001 Dec 29 [Sat]    327.6  -10.4    -51.5   62.3      ..    ..     ..
2001 Dec 30 [Sun]    324.1  -10.4    -52.3   61.1      ..    ..     ..
2001 Dec 31 [Mon]    322.3  -10.4    -52.7   60.6      ..    ..     ..
2002 Jan 01 [Tue]    320.4  -10.4    -52.9   60.4      ..    ..     ..
2002 Jan 02 [Wed]    318.6  -10.4    -52.8   60.4      ..    ..     ..
2002 Jan 03 [Thu]    315.1  -10.5    -52.3   61.2      ..    ..     ..
2002 Jan 04 [Fri]    313.2  -10.5    -51.8   61.9      ..    ..     ..
2002 Jan 05 [Sat]    311.4  -10.5    -51.1   62.8      ..    ..     ..
2002 Jan 06 [Sun]    309.6  -10.5    -50.2   64.0      ..    ..     ..
2002 Jan 07 [Mon]    306.1  -10.5    -48.4   66.4      ..    ..     ..
2002 Jan 08 [Tue]    304.2  -10.6    -47.2   68.0      ..    ..     ..
2002 Jan 09 [Wed]    302.4  -10.6    -45.8   69.7  << Sun sensor restarts  
2002 Jan 10 [Thu]    300.5  -10.6    -44.3   71.5  
..                                  
---------------------------------------------------

On Jan 09, when the Sun sensor recovers lock, the magnetorquer will be used
once again to:

 a) counteract the "mystery effect" precession (drift) in alon
 b) to drive alat towards alat=0
 c) increase alon towards alon=360 as rapidly as the Sun's movement allows.
 
Broadly the future should be:

  Date         Alon  Alat
  -----------------------
  2002 Jan 08   300  -10
  2002 Jan 15   300   -5
  2002 Jan 22   300    0
  2002 Feb 19   320    0
  2002 Mar 19   340    0
  2002 Apr 13   360    0
  -----------------------

Excellent communications are available now, and will be maintained throughout
this period.

JRM 2001 Dec 29 [Sat] 1414 utc
______________________________________________________________________________

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