Now within two years of reaching Saturn, NASA's Cassini spacecraft took test images of a star last week that reveal successful results from an extended warming treatment to remove haze that collected on a camera lens last year.

The quality of the new images is virtually the same as star images taken before the haze appeared. In the most recent treatment, the camera had been warmed to 4 degrees Celsius (39 degrees Fahrenheit) for four weeks ending July 9. Four previous treatments at that temperature for varying lengths of time had already removed most of the haze. The camera usually operates at minus 90 C (minus 130 F), one of the temperatures at which test images were taken on July 9 of the star Spica.

These five images of single stars, taken at different times with the narrow-angle camera on NASA's Cassini spacecraft, show the effects of haze collecting on the camera's optics, then successful removal of the haze by warming treatments. The image on the left was taken on May 25, 2001, before the haze problem occurred. It shows a star named HD339457. The second image from left, taken May 30, 2001, shows the effect of haze that collected on the optics when the camera cooled back down after a routine-maintenance heating to 30 degrees Celsius (86 degrees Fahrenheit). The star is Maia, one of the Pleiades. The third image was taken on October 26, 2001, after a weeklong decontamination treatment at minus 7 C (19 F). The star is Spica. The fourth image was taken of Spica January 30, 2002, after a weeklong decontamination treatment at 4 C (39 F). The final image, also of Spica, was taken July 9, 2002, following three additional decontamination treatments at 4 C (39 F) for two months, one month, then another month. Credit: NASA/JPL

"We're happy with what we're seeing now," said Robert Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The team will decide in coming weeks whether to proceed with another warming treatment later this year.

Cassini's narrow-angle camera worked flawlessly for several months before and after a December 2000 flyby of Jupiter. Haze appeared when the camera cooled back to its usual operating temperature after a routine-maintenance heating to 30 C (86F) in mid-2001. Lens hazing from engine exhaust or other sources is always a possibility on interplanetary spacecraft. Planners designed heaters for Cassini's cameras to cope with just such a situation.

Before treatment, the haze diffused about 70 percent of light coming from a star, by one method of quantifying the problem. Now, the comparable diffusion is about 5 percent, Cassini engineers Charles Avis and Vance Haemmerle report. That's within one percent of what was seen in images from before the hazing occurred, possibly within the range of statistical noise in the analysis.

Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Office of Space Science, Washington, D.C.