Spacecraft orbiting Saturn
2004-07-01 08:22
California - The international Cassini spacecraft threaded a gap between two of Saturn's dazzling rings and entered orbit around the giant planet, completing one of the mission's most critical manoeuvres more than 1.4 billion kilometres from earth.
Mission control at Nasa's Jet Propulsion Laboratory erupted in cheers shortly before 21:00on Wednesday (04:00 GMT Thursday) when a radio signal indicated Cassini had been captured by Saturn.
Propulsion engineer and mission commentator Todd Barber said the announcement came earlier than predicted because the signal had been tracked so well. Cassini's engine was to continue burning for another 12 minutes or so.
The manoeuvre, which brought Cassini within 20 112 kilometres of Saturn's cloud tops, came after two decades of work by scientists in the United States and Europe.
The craft could have simply flown past Saturn if the burn failed to brake its acceleration properly.
Cassini was programmed to perform a high-speed ballet, turning its big radio dish forward to shield against particles as it ascended through the rings, pirouetting to point its engine forward and fire, then spinning around to put the shielding antenna forward again for a descent back through the rings.
The $3.3bn mission, funded by US and European space agencies, was designed to give scientists at least a four-year tour of Saturn and some of its 31 known moons. Cassini is scheduled to make 76 orbits and repeated fly-bys of the moons.
Scientists hope the mission will provide important clues about how the planets formed. Saturn, the sixth planet from the sun and the second-largest, intrigues scientists because it is like a model of the early solar system, when the sun was surrounded by a disk of gas and dust.
Cassini has travelled 3.5 billion kilometres since it was launched in 1997, getting gravitational assists from earth and Venus as it caromed around the solar system.
The spacecraft took the roundabout route because the 6.6 metre -long, 3.9 metre wide craft was too massive to be launched on a direct trajectory to Saturn.
Cassini also carried with it a probe - named Huygens - to be sent into the atmosphere of Saturn's big moon Titan in January. The moon, blanketed by a thick atmosphere of nitrogen and methane, is believed to have organic compounds resembling those on earth billions of years before life appeared.
Cassini and its probe are named for 17th-century astronomers Jean Dominique Cassini and Christiaan Huygens.
Previous expeditions to Saturn were brief. There were fly-bys by Pioneer 11 and the Voyager missions from 1979 to 1981.
- AP