SXT REPORT FOR WEEKS 38 ; 12 Sep 1993 - 19 Sep 1993               

GENERAL STATUS

     Another week of smooth operations.  On Thursday, 16 Sep, the
Skew gryo was tested.  This is explained further in the report below.
Solar activity remained at a relatively low level.



PERSONNEL

     Many visitors were seen at ISAS last week as a result of the Kofu
meeting the week before.  By the end, most had returned to their homes
in the States or Europe.  Hugh Hudson is currently in the States until
next week and Sam Freeland and Greg Slater will return to the States at
the end of this week.  I will also make a short trip to Calif starting
tomorrow, and will return the middle of next week.  T. Shimizu will act
as the Chief Observer while I am away.  Next week's report (for Week 39)
will probably be combined with the report for the following week. 


SOLAR ACTIVITY

     Solar activity remained at a high A Goes level.  One C flare
occurred on 16 Sep, however, it occurred during spacecraft night.  Two
coordinated observing campaigns are being planned.  The first is with
the Norikura Observatory during 23-30 Oct, weather permitting.  The
scientific emphasis will be on plasma diagnostics.  The Norikura contact
is K. Ichimoto and H. Hara will be assisting the observations.  The second
is a bright point campaign begining on or 4 or 5 Oct. with Kitt Peak, 
organized by Karen Harvey.  


SCIENCE PROGRESS

     With the number of visitors, there were many opportunities for 
discussions.  Ron Moore found a nice example of an erupting flare on
15 November 1991 (but different from the famous 15 Nov event) and made
a short of video of this event for his talk at Mitaka.  Hugh Hudson's 
goes_reducer program, that estimates temperatures and emission measures, 
was improved by Pat Bornmann to give uncertainty estimates on those
parameters.  Dominic Zarro and Lemen worked extensively on the BCS
spectral synthesis and fitting software. The Thursday seminar included 
three speakers:  C. Schrijver (Utrecht), R. Hammer (Freiburg), and 
T. Nakagawa (Sendai).


SXT OPERATIONS

     The SXT operations went very smoothly this week and there were
no significant problems to report.


SPACECRAFT GYRO CHANGE

     The Y-gyro drift rate has been increasing since March 1993.  The
drift rate of all gyros at launch were approximately .1 deg/hour, but
the Y-gyro drift rate is currently approximately 5 deg/hour.  The drift
rate is not increasing monotonically, but has sometimes increased and
sometimes decreased over long periods (days to weeks).  The drift rates 
of the X and Z-gyros have not changed since launch and both remain below
0.1 deg/hour.  Despite its drift rate increase, the Y-gyro performance 
is still adequate for attitude control.

     On Thurs, 16 Sep, the NEC engineers turned on the S-gyro (skew)
to measure its drift rate.  This gyro was tested briefly two years ago
during the post-launch check-out period, but has not been turned on since.
The S-gyro drift rate was measured on Thurs to be 0.04 deg/hour, which was
essentially its launch value.  Because this rate is so much lower than 
the Y-gyro drift rate, it was decided that on Monday, 20 Sep, the 
spacecraft control would be switched from X-, Y-, Z-gyro's to X-, Z-, and 
S-gyro's.  This was accomplished during today's KSC contacts, and T. Kosugi 
has confirmed that there is an improvement in spacecraft attitude control.

     It should be noted that the performance of the Y-gyro is adequate
for attitude control and could be used in the future if there are problems 
with the X-, Z- or S- gyro's.  Now that the S-gyro is being used for
attitude control, we will have to modify the software for SXT image 
registration to use the correct transformation relations.

                                                  James R. Lemen
                                                  20 Sep 1993