0 May 2001 – During the coast phase between Jupiter and Saturn, it was noticed that "haze" became visible in the pictures taken by the narrow-angle camera of Cassini. This was first seen when a picture of the star Maia in the Pleiades was taken after a routine heating period.
23 July 2002 – In late January, a test was performed to remove the "haze" from the narrow-angle camera lens by heating it. Warming the camera to 4 degrees Celsius (39 degrees Fahrenheit) for eight days produced positive results. Later, the heating was extended to 60 days, and a picture of the star Spica showed an improvement of more than 90 percent compared to before the heating period. On 9 July, a picture showed that the removal procedure was completed successfully, which was announced on 23 July.16
16 NEWS - Press Release: Cassini Camera Haze is Removed July 23, 2002 https://web.archive.org/web/20061028020201/http://saturn.jpl.nasa.gov/news/press-releases-02/20020723-pr-a.cfm
which includes this image that I've zoomed:
Comparison images from Cassini camera
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.
The peak temperature reached during heating was +4 °C (normally -90 °C) so the haze was likely water, and the fact that the resulting image has a distinct annular appearance suggests it was due to somewhat monodisperse droplets on some optical surface.
Question: Where was the water buildup on Cassini's narrow-angle camera system?
Does it have to remain heated all the time now? Did it have to remain heated continuously?
- In which volume was the water trapped?
- On which optical surfaces did it cause the problem?
- Did the water get driven away or does the camera always have to run at +4 °C to run haze-free, or can it be operated at -90 °C?