The world's largest and most expensive interplanetary satellite, Cassini, and its piggy-backing partner, Huygens, are finally on their way on a 2,200-million-mile journey to Saturn.
The pair were carried aloft at 9.43 a.m. (Irish time) on a Titan IV-B rocket from Cape Canaveral, Florida, in what the US National Aeronautics and Space Administration described as a flawless launch. NASA, however, did not get off so lightly.
The controversy and protests which surrounded the use of radioactive plutonium to power Cassini's electrical system during the long cold flight to Saturn has dented NASA's image, both in the US and abroad. Before Cassini, protests in the US against NASA satellite launches were unheard of and its manned and unmanned missions into space were invariably celebrated rather than criticised.
Protesters claimed that plutonium could spread over a wide area and cause thousands of cancers if the satellite exploded during lift-off. NASA countered by saying the heat-resistant iridium and graphite-encased plutonium would simply fall to Earth unbroken for later pick-up. It also pointed out that plutonium had been used without incident during other satellite launches.
This argument is now moot as Cassini is already safely on its way, but we can expect a replay of the plutonium controversy in July 1999 because of Cassini's convoluted and roundabout flight path towards Saturn.
The probe orbits the Earth for a time before heading for the planet Venus on one of four planetary fly-bys, gravity-assisted boosts that will eventually push its speed up to 100 km per second. It swings around Venus in April 1998, and again in June 1999, before returning to Earth for a close-quarters fly-by in July 1999 which will have Cassini flash past 500 miles overhead.
Protesters believe there is a real chance of the satellite missing the target and burning up in the Earth's atmosphere, spreading plutonium dust right around the world. NASA says the chances of re-entry are about one million to one, but distribution of the plutonium won't happen because of its shielding and also because it is in ceramic pellet form.
In their response to this position, a group of international planetary scientists issued a statement days before the launch which said they were satisfied that the risks "had been thoroughly and honestly assessed" and that the health risks in the event of an accident were "negligible".
For all of the controversy, the Cassini/Huygens flight is a remarkable undertaking, with all the drama and adventure of the best of satellite missions. Two-and-a-half storeys tall, Cassini weighs in at 5.6 tonnes and is named after the 17th-century astronomer, Jean-Dominique Cassini, who discovered Saturn's rings.
While it is mostly American, its companion satellite, Huygens, is mostly European, and is named after Christian Huygens, a Dutch scientist who discovered Saturn's moon, Titan, in 1655.
The mission cost £2,100 million and has so far taken 13,000 work-years by US and European scientists, about half of what it took to build the great pyramid of Cheops in Egypt.
The satellite pair will slingshot past Earth in 1999 and then get a final boost from Jupiter in December 2000, before finally arriving at Saturn on July 1st, 2004.
Cassini will orbit Saturn for four years carrying a battery of experiments to study the planet and its complex system of rings and moons. Huygens, meanwhile, will break off on its own little adventure, a landing on the surface of Saturn's largest moon, Titan, during November 2004.
This moon, about the size of the planet Mercury, is of particular interest to scientists because it has a dense organic atmosphere made up of nitrogen, methane and more complex carbon-based molecules. They also believe that hidden at frigid ground level are lakes of ethane over a thin layer of frozen methane and ammonia, which in turn sit on a layer of frozen water ice.
This mix intrigues scientists because many believe the Earth's primordial atmosphere was very similar, although warmer. Though life on Titan is unlikely due to the extreme cold, an analysis of its atmosphere may provide valuable clues to the chemistry of early Earth.
Huygens will plough into this atmosphere at 20,000 km-per-second, a heat shield will prevent it from burning up. A succession of parachutes will slow the probe as it descends. The satellite will study the atmosphere, relaying data back to Cassini. It will study Titan's weather and winds and analyse the chemical haze that hides the moon's surface.
It carries a surface science package but researchers don't know whether it will land on a solid or liquid surface. In either case, Huygens will continue to send data back to Cassini for some hours before its batteries fail and it goes forever silent, having completed its one-way mission.