NASA's Cassini spacecraft continues to fly in good health with less than 29 months to go before it becomes the first Earth envoy to enter orbit around Saturn.

Last month, Cassini completed a 40-day period of data collection as part of a multi-year search for gravitational waves. The data comes from radio transmissions between Cassini and stations of NASA's Deep Space Network in California, Spain and Australia.

The experiment used frequencies both in the X-band, which is the band commonly used by interplanetary spacecraft, and in the higher-frequency Ka-band, a new band for the Deep Space Network. Data was successfully collected for 90 percent of the possible transmission time in the Ka-band, a promising beginning for future uses of that band by Cassini and other spacecraft. In the traditional X-band, data was received for 98 percent of the possible time over the 40-day experiment.

Gravitational waves are ripples in the fabric of space and time that are set off by acceleration of massive bodies, such as black holes or supernovas. Their existence has been confirmed indirectly, but never detected experimentally. This search assesses the Doppler effect on radio waves traveling between Cassini and Earth. The Doppler effect is how the frequency of a transmission is affected by the relative speed between the sender and receiver, such as the raised pitch of an approaching train's whistle.

Scientists are looking for barely perceptible fluctuations that would be caused in Cassini's speed relative to Earth if gravitational waves of certain wavelengths were traveling through the solar system. They expect analysis of the data to take months. Cassini will be used for two more periods of gravitational wave investigation before it reaches Saturn.

Engineers are making progress at correcting a problem of haze on the spacecraft's narrow-angle camera. Warming the camera for a week to a temperature just above freezing has significantly reduced the problem, so that treatment will be repeated for a longer period beginning March 5.

"We're fully confident it is going to get better," said Robert Mitchell, Cassini-Huygens program manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The usual operating temperature for the camera is minus 90 Celsius (minus 130 Fahrenheit). Haze on its optics appeared when it was cooled to that temperature after a routine-maintenance heating of the instrument to 30 C (86 F). That occurred following flawless imaging of Jupiter for several months of 2000 and 2001. Heating the camera again, but to only 4 C (39 F), is removing the haze. Test images taken of a star in late January showed the improvement.

Cassini will reach 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 on Jan. 14, 2005. 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.