Navigators Prepare for Scheduled Trajectory Refinements
February 3, 1998
The Cassini spacecraft remains in excellent health as it travels on its Saturn-bound trajectory at a speed of approximately 120,000 kilometers per hour (about 75,000 miles per hour). The spacecraft has traveled more than 271 million kilometers (about 168 million miles) since launch last October 15.
Cassini continues to fly with its 4-meter (13-foot) diameter high-gain antenna pointed toward the Sun so that the rest of the spacecraft is shaded. It will maintain in this attitude, except during planned trajectory adjustments, for the first 14 months of flight as it travels through the inner solar system.
Radio communications with the spacecraft are currently through low-gain antenna 2, one of the spacecraft's two low-gain antennas. Low-gain antenna 2 is located at the end of the spacecraft opposite the high-gain antenna. The low-gain antenna that is selected for a given period depends on the relative geometry of the Sun, Earth and the spacecraft. The telemetry data rate from Cassini is currently 40 bits per second.
For about the next month, there will be an increase in the amount of telecommunications time allotted to Cassini by NASA's Deep Space Network to meet the data needs of spacecraft navigators as they prepare for two long-scheduled trajectory refinements. In late January, Deep Space Network antennas were trained on Cassini about four times a week. In February, those episodes of tracking will be approximately doubled. The adjustments will be made in preparation for Cassini's flyby of the planet Venus on April 26. The additional data gathered through the extra telecommunications time are used to refine knowledge of the spacecraft's location, which will aid navigators in setting precise parameters for the trajectory adjustments, such as the duration of thruster firings.
Additional information about Cassini-Huygens is online at http://saturn.jpl.nasa.gov.
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.