Mission Status Report
Mission Status Report #11 Star Date: July 21, 1999
Mission Status Reports on the web page will occur when news-worthy
events occur (but at least weekly!) for the time being.
-- Bill Blair
Image: Portion of "first light" image with the FES-A Guide Star
(Click image to see full field of view version.)
FUSE GUIDE CAMERA SEES FIRST LIGHT;
FUSE TRACKS ON STARS!
The FUSE satellite remains healthy and the In-Orbit Checkout phase is still in
progress. Thermal control still has the satellite in
"bake-out" mode to drive any trapped gases out of the structure prior to the
beginning of normal operations.
We have opened one of four telescope baffle doors
and actually taken a picture on the sky with one of the Fine Error Sensor (FES)
CCD guide cameras on the satellite (see above). FUSE scientist Ken Sembach
was even able to identify exactly where we were pointing at the time and has
identified two galaxies and several HST Guide Star Catalog stars in the field
of view. This was a 1 second exposure visible light image from July 14, 1999,
and the pointing direction is near the south pole of the orbit in an area
of continuous viewing availability known as the CVZ (Continuous Viewing Zone --
in other words, a region of sky where the earth never gets in the way). We
will remain pointing in the CVZ for at least the next month or so to avoid
pointing the telescopes at the sunlit earth, where reflected solar UV light could
potentially cause damage to our sensitive optics.
From analysis of this image, we can tell that focus is near nominal and the
camera is in good working order (as expected from earlier tests prior to
door opening). We can readily see stars down to about 17 magnitude (much fainter
than will actually be used for guiding the telescope). On the down side, some
exposures taken on the daylit side of the orbit show a higher incidence of
scattered light than we expected. Only limited data are available, however,
and this could be due to a particular orientation of the spacecraft at the
time of these exposures. Analysis and more data taking are on-going.
Over last weekend, we also performed our first tests to demonstrate actual tracking
and guiding capability. First we simply told FUSE to take a picture, process it
(onboard), find some stars, and lock onto them. (This is called "guiding on
unknown stars.") This worked well, and the initial pointing stability looks
excellent. However, with the "coarse guidance" information available, we only
know where FUSE is pointing to within about 2 degrees. So next, we executed a
procedure that allowed us to identify the exact star field we were seeing and
send an update to the satellite to tell it where it was pointing exactly.
(We euphemistically call this procedure "Found in Space!") It worked! This
same procedure will be run anytime we lose fine pointing information to get us back
on track, but getting through it the first time gives us confidence that all
parts of the system are "talking" to each other properly.
All of this is still being done with only one telescope door open. Over the
next week we hope to perform more guiding tests and open the remaining
telescope baffle doors in preparation for the focus and alignment of all four
Reported by: Bill Blair, Chief of Mission Planning
CSA Press Release on FES First Light Image
in English and