Status Report

FUSE Mission Status Report #58 May 28, 2002

By SpaceRef Editor
May 28, 2002
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FUSE Capabilities Continue Expanding

The FUSE satellite continues to operate well after our recovery from Reaction Wheel problems.
With each passing week, we are also learning more about our new control system and how it behaves both
for slewing (moving between targets) and for static pointing stability. Since the recovery, we have been
restricted to observing targets at absolute declinations (or celestial “latitudes” if you will) higher
than 40 degrees (that is, above +40 degrees in the north or below -40 degrees in the south) in regions
where we can keep FUSE pointed stably during science observations. During the last month, we have demonstrated
observing strategies that have allowed us to successfully observe two targets well below 40 degrees
declination, in the zone that is unstable much of the time. Using new software that predicts temporary
regions of stability, we observed targets at declinations of 23 and 8 degrees! Each target was observed
several times over the course of a week as part of a monitoring program for a Cycle 3 Guest Investigator

This is a great step forward in our attempt to return FUSE to full-sky coverage. With the current capability
and understanding, we can now access about 75% of the celestial sphere at one time or another during the
year! (This is up from about 40%.) We now need to take what we have learned from these initial attempts
and incorporate it into our planning software to make scheduling these observations more standardized.
Also, we have other ideas to test out that will no doubt open things up further. We are extremely
pleased with progress to date.

As further evidence of the robustness of operations, I recently pulled together a summary of performance
of the mission since February 1, 2002 (just after operations were restarted). I am pleased to tell you that
we have observed over 300 new science targets during this time, for a total of over 4 million seconds of science
exposure time! Our science efficiency (on target time compared to the wall clock) over this time has been 35%,
compared with a mission average 28% prior to December 2001. This is excellent performance for a low earth orbit
mission, and clearly demonstrates the effects of being forced to observe primarily at high declinations where
visibility intervals a longer on average. Hence, while this efficiency number may drop some as we start
incorporating more low declination targets, it is still very important for us to maximize the target
availability at higher declinations to maximize the scientific return from FUSE.

On another front, the semi-annual American Astronomical Society meeting is next week in Albuquerque, NM.
Over 25 FUSE-related presentations are on the docket for that meeting, including a series of talks
about the FUSE recovery effort. If you attend the meeting, I hope you can come to that session and
hear more details about the process we have been through. It has been (and continues to be) an amazing

Reported by: Bill Blair, Chief of Observatory Operations

SpaceRef staff editor.