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Planetary News: Cassini-Huygens (2004)Cassini-Huygens Settles into Orbit Around Saturn; Mission's International Team Celebrate
By A. J. S. Rayl Yesterday at 10:58 p.m. PDT, close to two hours after the end of the orbit insertion burn, Cassini-Huygens plunged back through the gap between Saturn's F and G rings, moving from the northern backlit side of the rings to the southern sunlit side. According to Jeremy Jones, Cassini's chief navigator, the spacecraft's current orbit takes it around the planet every 116.3 days. "We were aiming at 117.4 days, so we're right there" said Jones. An orbit correction scheduled for Saturday, July 3, will fine-tune the orbit of Cassini-Huygens. At a press conference held at the Jet Propulsion Laboratory in Pasadena on the night of the orbit insertion, Cassini-Huygens team members and leaders from NASA, ESA, and the Italian Space Agency, the three agencies sponsoring the mission, celebrated the night's success. "Here we are sitting on this pale blue dot..." said Associate NASA Administrator Ed Weiler. "We just landed twice on Mars, flew by a comet . . and now we're about to go into orbit around a planet a billion miles away. How do we get away with having so much fun?" David Southwood, Director of Science at the European Space Agency (ESA) was gracious in his thanks to JPL's Cassini team. "This was America doing it right," he said. "Thank you JPL, thank you USA, thank you NASA . . . it was a very professional show." Navigator Jeremy Jones summed up the general feeling: "It is a beautiful night; the spacecraft flew absolutely flawlessly." June 30, 2004, 9:23 p.m., PDTAt 9:12 p.m. PDT, exactly one second ahead of schedule, Cassini completed its 96 minute engine burn and entered orbit around Saturn. As expected, the firing of the engine slowed down the spacecraft and enabled it to be captured by Saturn's gravity and enter orbit around the planet. Despite the burn, Cassini-Huygens' speed actually increased during the 96 minutes from 24.4 kilometers per second (54,500 miles per hour) to 30.0 kilometers per second (67,000 miles per hour) because of Saturn's strong gravitational pull. Were it not for the engine burn, the spacecraft would have accelerated far more and continued on to the outer reaches of the Solar System. During the burn, mission controllers at JPL followed the spacecraft's progress by tracking the Doppler shift of the radio signal from the Low-Gain Antenna. Throughout the entire maneuver the spacecraft's speed followed the predicted speeds with remarkable precision. During the next hour Cassini will be studying the rings of Saturn from close by. This is the closest the spacecraft will approach the rings during Cassini's entire mission. The spacecraft will then plunge back through gap between the F and G rings. Cassini-Huygens is now part of the Saturnian system. June 30, 2004, 7:36 p.m., PDTAt 7:36 p.m., precisely on time, the Doppler signal from Cassini's Low-Gain Antenna indicated that the 96-minute orbit insertion burn had begun. The 70-meter dish at Canberra, Australia, as well as the 34-meter dish at Goldstone, California, are maintaining contact with the spacecraft through the carrier signal from Cassini's Low-Gain Antenna. June 30, 2004, 7:29 p.m., PDTAt 7:11 pm Pacific Daylight Time, flying at over 14 kilometers per second (31,000 miles per hour), Cassini-Huygens has successfully completed its ascending passage through the rings of Saturn. With its High-Gain antenna pointing the way and shielding the spacecraft from rock and dust particles, the spacecraft flew successfully between the sparse F and G rings. The first signal from the spacecraft confirming the successful passage was received at 7:30 pm, when the Low-Gain Antenna was pointed towards the Earth. Although telemetry from the spacecraft is not available at this stage, the control team at JPL is able to maintain contact with the spacecraft through a faint tracking signal sent out by Cassini's Low-Gain Antenna. The speed of the spacecraft can be determined through the Doppler effect, which causes the frequency of the transmission to shift in accordance to the spacecraft's speed relative to the receiving stations on the Earth. Despite concerns earlier today, the 70-meter dish at Canberra, Australia, is fully operational and was available to receive the transmission from the spacecraft. It is the only antenna in NASA's Deep Space Network sensitive enough to receive signals from Cassini's Low-Gain Antenna.June 30, 2004, 11:30 a.m., PDTLatest weather reports from Australia indicate that the 70-meter dish at Canberra, Australia may have to be stowed away due to high winds. This antenna is the only one in NASA's worldwide Deep Space Network sensitive enough to detect the signal from Cassini during the orbit insertion maneuvers. If the dish is not operational scientists will have to wait several more hours before contacting the spacecraft. The orbit insertion itself will not be affected in any way. "We can control things better on Saturn than on Earth," commented Cassini Project Manager Robert Mitchell. Because of Cassini's orientation at the end of the burn, the signal will be transmitted by the spacecraft's Low-Gain Antenna. Most subsequent signals will be transmitted by the High-Gain antenna, and will be received by several listening stations around the world. |
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