Cassini Mission Status 11 Feb 2002

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.
Additional information about Cassini-Huygens is available online
at http://saturn.jpl.nasa.gov .