REPORT FROM ISAS,  29-MAY-1992, 2231 JST.

Greetings,

Observing with YOHKOH and SXT continues on a routine basis.  In the
course of the last 2 weeks we have completed one more apogee transit
through the dreaded radiation belt.  Multiple single event upsets (SEU)
were experienced and 2 unexplained filter hard errors (filter not
achieving the desired position after 3 tries).  We do not believe that
this represents a mechanical or bearing problem because no soft errors
have been recorded (soft error is when the filter wheel does not
position correctly the first time but does on the second or third try)
and both hard errors took place during a day command activity.  Sam is
trying to puzzle out the reason for these hard error indications. 

Strong, Nitta and Morrison have returned to the US for short trips. 
Acton, Hudson and Freeland are the resident U-side SXT personnel. 
Culhane has been here for nearly 2 weeks, much to our delight.

Sam Freeland has installed and tested his on-board and ground software
to facilitate recovery from SEUs.  This seems to have been completely
successful and should be a great benefit to scientific operations as the
disruption caused by the difficulty of recovering from these events up
to now has been substantial.  Yea, Sam!!

For the past week we have been tracking a single active region under the
mode ARS2 (Active Region Selection, mode 2).  In this mode the search
for the brightest x-ray point is only done over a 2.7x2.7 arcmin box
about the latest pointing address instead of over the entire active belt
as is done in ARS1.  Thsi mode is necessary for effective coordinated
with ground based observers and campaigns such as the Max '91 CoMSToC
activity.  The mode is working beautifully on NOA Active Region 7117 and
some truly spectacular active region movies are being produced with a
1/2 minute time resolution.  This big region has not been productive of
flares but has been sufficiently bright that we have stopped taking 15
second full disk exposures.  Some work has been done tweaking the
standard SXT observing tables and Friday we did the first routine run of
a table with optical and CCD gain calibration.  Next week we will
prepare and run the routine dark frame table.  It is planned to run each
of these tables one set of invisible orbits each week.  They have been
written in such a way as to not unduly impact the normal full frame
movie sequence.

Production of Exabyte data tapes for distribution is moving ahead
although a quantitative report will have to await the return of Mons
Morrison.  However, it is gratifying that the first tapes have now been
read by users successfully.  This is more of a big deal than it sounds
because all of the analysis software is distributed on the tape AND the
software for installing it.  Furthermore, the whole business has to be
machine independent between several types of machines and both Unix and
VMS operating systems!  Kudos go to Sam Freeland, Mons Morrison, Jim
Lemen and, especially, to Gary Linford for this major accomplishment. 
Recall that these tapes include all of the YOHKOH data, not just SXT.

Some 30 YOHKOH papers have been submitted for the Astronomical Society
of Japan meeting at Osaka in May and a similar number are planned for
submission to the Publications of the Astronomical Society of Japan at
the end of April.  These opportunities consitute the official "first
release" of YOHKOH scientific results.  Thus, the author lists are long
in order to recognize the many individual who have made this fantastic
mission possible.  Tomorrow and Tuesday there will be a meeting here at
ISAS designed to discuss scientific results, calibrations, etc., for
those working on these first papers.

					Loren W. Acton