The Cassini-Huygens Visit to Saturn by Michael Meltzer

Author:Michael Meltzer
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

7.2.5 Preparing for the second Venus flyby (Venus-2)

7.2.5.1 TCM-5: Maximizing the second gravity assist

At the beginning of December 1998, Cassini-Huygens successfully completed a long-planned, hour-and-a-half rocket engine burn (TCM-5) that slowed down the spacecraft by 450 meters per second (about 1,000 miles per hour) in order to adjust its trajectory for the second planned gravity assist (Venus-2), which would occur six months later.31 The TCM-5 engine firing was one of only two long burns planned for the entire mission; the second occurred when Cassini reached Saturn in July 2004 and braked in order to achieve an orbit around the planet.

The flight team continued to conduct checkouts of the spacecraft’s instruments as it sped toward its second Venus encounter. The team radioed commands to operate its optical instruments, including its imaging system, Visual and Infrared Mapping Spectrometer, and Ultraviolet Imaging Spectrograph. The instruments sighted on the bright star Spica, using it as a calibration and pointing target. The team then used data returned from the test to generate a photomosaic of Spica and the surrounding sky. From this, the pointing accuracy of the spacecraft and its optical instruments was determined.32

The portions of the cruise phase that occurred away from planetary gravitational fields provided ideal opportunities to calibrate accelerometers and prepare them for use at Saturn. In particular, checkouts of the Probe’s Huygens Atmospheric Structure Instrument (HASI) in the zero-gravity environment of the cruise phase allowed an extremely accurate assessment of its accelerometer measurements.33

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