All the ACE instruments observed a large solar energetic particle event
which started on April 20th.

Around 12:00 UT on April 20th, the image intensifier on the CRIS instrument
was automatically turned off when an internal current limit was reached due to
the high proton flux impinging on the CRIS trajectory detector. This
effectively disabled the CRIS instrument until 17:00 UT on April 23rd, when
the proton flux dropped sufficiently for the image intensifier to be turned
back on. Note: the CRIS instrument was not designed to operate during periods
of high solar activity. The instrument continues to operate normally.

Trigger thresholds were raised on the SIS instrument to optimize the
response to heavy ions during the solar event. Changing the thresholds
affected the calibration of the real time solar wind proton data from
SIS. The threshold were returned to their nominal levels following the
event.

On April 21, as part of a test, the ULEIS Start-2 time-of-flight high
voltage was comanded off in order to gain information on the operation
of the instrument's timing electronics.  This turn off will not affect
ULEIS browse parameters.  The ULEIS team will later decide when to
restore the Start-2 time-of-flight high voltage to nominal values.

Today (5/1/98) ACE will be performing the 4th Station Keeping maneuver.
The amount of fuel usage is minimal (approximately the same as the
weekly attitude maneuvers)  In addition an attitude maneuver will also be
performed.  The fuel usage for the SK-4 will be ~64 grams and the attitude
will use 50-60 grams.