The Cassini/Huygens mission was set to lift off from Cape Canaveral in Florida on 13 October. The flight was delayed, not because of protests by environmentalists, who are concerned that the craft is carrying plutonium, but because of strong winds and technical problems. NASA officials tried a second successful attempt on the 15 October.

A joint mission between NASA and the European Space Agency (ESA), the Cassini spacecraft is designed to orbit Saturn – exploring the planet, its satellites and rings – while the Huygens probe will examine Titan and its atmosphere. The £2.2 bn mission is due to arrive at Saturn on 1 July 2004.

Cassini/Huygens will carry 24 experiments – 18 on the orbiter and six on the probe. The Cassini spacecraft will try to discover more about Saturn’s interior structure, the chemical composition of its rings and how many satellites it has. Its instruments will gather optical and microwave images of Saturn, its satellites and rings, and will also analyze the planet’s magnetosphere and the particles trapped in it.

Some of the Cassini instruments will also gather data en route to Saturn. A cosmic dust analyzer, for example, will examine interplanetary and interstellar dust on the way to Saturn and on arrival will study the planet’s rings. “We know that interstellar dust is passing through the solar system and could even be reaching the Earth, ” says Eberhard Grün of the Max Planck Institute for Particle Physics in Heidelberg, Germany, who is principal investigator on the experiment. “Interstellar dust is extremely interesting stuff. It is very important as it is what the planets are made of, ” he says.

Four months after arriving at Saturn, the Huygens probe will separate from Cassini and make the 22-day journey to Titan. Researchers are particularly interested in Titan because it is thought to resemble the Earth as it was before life began – its nitrogen atmosphere is thick with carbon compounds.

The Huygens probe will parachute through Titan’s atmosphere, making measurements of its physical and chemical properties as it descends. After its journey of more than seven years, the probe will take data for just two hours and 15 minutes – and researchers do not even know whether it will then hit a solid surface or a molten one. “It is due to arrive on 27 November 2004 – that’s a Saturday if I remember right, ” says Michael Bird of Bonn University, who is principal investigator on an experiment to measure Titan’s wind speeds.

To reach Saturn, Cassini/Huygens will make a series of slingshot manoeuvres, using the gravitational pull of Venus, the Earth and Jupiter. Even if the launch passes off without any problems, environmental protesters are concerned that the spacecraft could crash back to Earth as it swings by in August 1999. Electrical power for Cassini and its instruments will be provided by three radioisotope thermoelectric generators containing about 33 kg of plutonium. Protesters are concerned by the consequences of any accident. However, NASA says that the chances of any accident are minimal. A similar campaign failed to halt the 1989 launch of the Galileo mission to Jupiter.