FUSE 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 Camera.

(Click image to see full field of view version.)


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 telescopes.

Reported by: Bill Blair, Chief of Mission Planning

Related Links:

CSA Press Release on FES First Light Image in English and in French.

Return to the List of Status Reports