Status Report

Extreme Ultraviolet Explorer (EUVE) Operations Highlights: 27 January – 2 February 2001

By SpaceRef Editor
February 2, 2001
Filed under ,

EUVE) This was the final week of Extreme Ultraviolet Explorer (EUVE) mission operations. Up to the end,
all satellite systems continued to perform exceptionally well. During
the week the Flight Operations Team (FOT) conducted
end-of-life/-mission tests on both the science payload and the

For the payload, the FOT tested the operation of the backup (i.e.,
redundant) high voltage power supplies (HVPS) for the seven payload
detectors. FOT engineers turned on each HVPS and then ramped it up to
operational voltage levels. The resultant detector images were very
good, indicating that the HVPS units were working extremely well after
over eight years in non-operational hibernation.

For the spacecraft, the FOT conducted two battery tests. The first
was a test of how well the satellite would run on a single-battery.
One battery was removed from the load path and the other was used to
run the satellite systems (the third battery failed in May 2000). All
systems worked well, although upon entry of the spacecraft into
orbital day, the solar arrays pumped >50 amps into the single battery.
Concerned about a possible battery melt-down, the power engineer then
aborted the test.

The second spacecraft test was one to measure the remaining capacity
of the 50 amp-hour batteries. Both batteries were removed from the
recharge cycle and allowed to discharge to extremely low levels over a
number of orbits — at their lowest point the batteries reached 9%
state-of-charge (SOC; the normal low SOC is ~90%)! At that point the
load bus voltage dropped below its rated minimal operational level of
22 volts, and the FOT then commanded the systems back into recharge
mode; the batteries then returned to ~100% SOC with a few orbits. The
resultant data from these various tests is currently being analyzed,
and the results will later be distributed.

Finally, on 31 January the Project held a “celebratory wake” in the
EUVE control center, which was well-attended by local EUVE affiliates,
two representatives from NASA Headquarters, and a number of others
from GSFC and elsewhere via telephone. A live Webcam had also been
set up to help remote persons participate in the festivities. The FOT
had scheduled communications via the omni antennae right up to the
official mission termination deadline at 00:00 GMT on 1 February.
Prior to the deadline the FOT commanded the spacecraft to safe-hold
mode, and at ~23:59 GMT reconfigured its communications for STDN mode,
after which telemetry contact was lost.

However, the mission refused to end! The FOT had left the EUVE
transmitter on via the low-power omni antennae, in hopes that UCB’s
HESSI ground station could be used to periodically monitor EUVE.
However, after the official mission termination, GSFC decided that it
didn’t want the transmitter left on for fear of its possible
interference with other satellites. So, after much hassle to repower
the UCB and GSFC ground systems and establish the communications link,
at ~20:20 GMT on 2 February the FOT said its last words to EUVE and
commanded the transmitter off, which was immediately validated by a
loss of telemetry; in the blind the FOT then reconfigured the
spacecraft to STDN mode. The spacecraft was then set adrift: in
safe-hold mode, with transmitter off and receivers on via the omni,
and configured for STDN communications. A new re-entry prediction
show a mean re-entry date of 17 March 2002 (+/- 3 months at the two
sigma level).

The EUVE Project at UCB would like to offer its congratulations and
thanks to everyone associated with this tremendously successful
mission! We at UCB feel very honored and privileged to have been
given the opportunity to run the mission for the past four years. It
is with mixed feelings that we terminate this mission — joy at EUVE’s
scientific and technical excitement, opportunity, and challenge, yet
sadness in the premature loss of an old and true friend.

SpaceRef staff editor.