To:sot_shift
from: Dan Schwartz
date: 06 Sep 99, 02:00pm EDT
Subject: SOT shift report, Shift L46
--------
See http://asc.harvard.edu/acis/SOT_reports/sot-shift.html, or 
/proj/ascwww/AXAF/extra/science/htdocs/acis/SOT_reports/Sep_06_1999_L46.txt.

Shift L46
	Start at 249:10:00  GMT
		 = 06:00am 06 Sep EDT
	End	   02:00pm 06 Sep
   
SOT Lead	DAS
Spac/Aspect	RAC
FOT/Sci liason	
HRC		
ACIS 		

(Times will be given in GMT on day 249. In general
times are rough, not precise.)

PLAN
Run under load P11.
In radiation belts. Maneuver to intermediate position.
Retract LETG with real time commands. Insert and retract LETG
  via software commands.

EVENTS
Start of shift. OBSID = 62391. Intermediate position at 6hr40m, -45deg.
	Tracking 5 stars. (Fid lights are not commanded for these
	intermediate positions.)
12:02 Resume SAP 8M016 at step 9 for hardware retraction of LETG.
12:11 Confirm retract of LETG.
12:30 LETG insertion by software command
12:35 Letg retraction via software command (8M016.13)
SSR Playback
13:50 LOS

NOTES/ISSUES/PROBLEMS
Gratings MCE relay was switched to LETG for hardware insertion and
retraction. In this configuration, 6.7 volts were seen on B side, as 
in the HETG case. For the software insertion and retraction, the
relay was switched back to the HETG configuration, and we did NOT
observe 6 volts on the B-side drive input.  This gives high
confidence that what has been observed is a back EMF induced on the
B-side drive, and appearing in telemetry when connected to the RCTU
DC to DC converter. This can be avoided in future by 
configuring the relay to the grating opposite to that being driven,
but we need to decide if we really want to drive the relay 
each time.  Also, circuit analysis needs to evaluate the
advantage of keeping the 6v, which in any event is induced on
the B-side windings, out of the RCTU converter. 

During the LETG retraction, we saw rates 
within a factor of 2 of those which would trip the momentum 
monitor. To avoid any chances of going into an unnecessary safe
mode, we need to build load P12, and future loads until further 
notice, so that the spacecraft momentum monitor is disabled during
all grating motions (HETG or LETG). (This also requires disabling
autonomous momentum unloading.) In P12 the two grating movements
are accompanied by SIM translations, so the monitor disable 
operations in place for the SIM may be sufficient. Needs MP
attention,  and scrutiny by all at the Tuesday review of P12
products.

Why aren't fid lights commanded during intermediate pointings?
I suggest reviewing whether fid lights should be tracked during the
intermediate positions, such as OBSID 62391.  In my opinion they
should be, since they are giving information on the dynamics 
and thermal/alignment effects. 

-------------------------------------------------------
Dan Schwartz,	MS #3
das@head-cfa.harvard.edu  
phone: (617)495-7232    FAX:   (617)495-7356
cell phone: (617)512-5627   
pager: 800-759-8352 PIN 1636502
       or e-mail 1636502@skytel.com 
-------------------------------------------------------