Tohban report for Nov 3-10, 2003

Solar Activity:
The highlight of the week was the X-28 event on Nov 4 from AR846 at the 
west limb.  RHESSI observed the first half of the rise and much of the 
decay but unfortunately the peak was eclipsed.   Following this event, 
activity declined to very low levels after the region passed off the 
visible disk.  A 'micro-events' campaign of quiet sun observatins 
featuring RHESSI and TRACE was initiated on Nov 8 at 0 UT.

Spacecraft operations:
Normal data acquisition and operations went smoothly.  Because of the 
high level of activity, only 1-3 automated attenuator operation was used 
until late in the period when the normal 0-1-3 operation was enabled. 
Memory management was not an issue.

Other matters:
1.  Due to the gradually rising coldplate temperatures, on November 6 
the cooler power was increased from 63 to 75 watts (subsequently 
relaxing to 73 watts).  A rough optimization of balancer phase was 
performed at the same time.  The increase in power resulted in a cold 
plate temperature drop of ~1 degree and an increase in vibration levels 
to ~40 mg.

2.  Recently, the automated attenuator operation has appeared unusual in 
that the thick shutter has remained in place without apparent 
justification.  This was traced (by ML) to a combination of high 
particle count rates at high latitudes (due to the spate of X-flares) 
which triggered the shutter in and an enhanced level of noise in 
detector 5 which prevented it from being removed.  (Detector 5 is one of 
the 4 detectors which influence the software decision on shutter state.) 
  The high voltage on detector 5 was reduced slightly on Nov 10 to solve 
the problem.

3.  Recently, the imaging axis has been outside the SAS 6-limb-solution 
field-of-view for an unacceptably large fraction of the time.  An 
analysis by MF showed that the rotation axis offset from sun center was 
frequently larger than 8 to 10 arcminutes which, when combined with the 
offset (in the rotating frame) between the axis of rotation and the 
imaging axis, results in once-per-rotation intervals when the imaging 
axis is too far away from Sun center to get 6-limb solutions.  Daily 
plots of the radial offset of the spin axis vs time sometimes show a 
pattern in which the spin axis to sun center distance is only being 
reduced during a ~20 minute period in the middle of the daytime portion 
of each orbit.  At other times (including night) the offset increases at 
the expected sidereal rate of ~2.5 arcminutes per hour.  The current 
hypothesis is that the daylight periods of no correction are due to 
magnetic field orientation and that the remaining period (for which the 
aspect control system has effective authority) is too short to fully 
compensate for sidereal motion.  The possibility of increasing the limit 
of torque rod current is being investigated as a solution to this problem.

Respectfully submitted

gordon hurford