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Programme Manager, Bob Mitchell
"We should have some spectacular pictures of Saturn"
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Sue Nelson reports for the BBC
"Plutonium dust is deadly if inhaled"
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Wednesday, 18 August, 1999, 13:47 GMT 14:47 UK
Saturn probe swings by Earth

The Earth flyby will boost Cassini's speed on its way to Saturn
The plutonium-powered Cassini probe successfully swung past Earth, skimming within 1,170km (727 miles) of the planet on its way to Saturn.

A mission control spokesperson said simply: "It's on its way out," after the spacecraft received a gravitational slingshot to send it on the final leg of its seven-year mission.

Cassini is the largest and most expensive unmanned spacecraft launched by the US space agency, Nasa.

It carries with it more than 32kg (70 pounds) of highly radioactive plutonium.

Environmental groups had warned of the possibility of an accident, which would risk spreading poisonous carcinogenic plutonium dust around the world.

Boosted speed

However, scientists said they calculated the chances of such a mishap as about one in 1.2 million - and in any case, they said, the plutonium core is well protected.

Anti-nuclear protesters fears proved unfounded
The probe's nearest approach to Earth came over the south-eastern Pacific Ocean, above the Easter and Pitcairn islands.

In comparison, most space shuttle flights orbit at about 210km (130 miles) from the Earth's surface.

The effect of the Earth's gravity is expected to boost its speed from about 56,000 km/h (35,000mph) to more than 74,000km/h (46,000mph).

Scientists have been using planetary "gravity assists" since 1973 to fling probes to the outer Solar System.

"It's purely gravity and no more sophisticated than the Moon moving around the Earth," says Cassini programme manager Bob Mitchell.

He added that a Nasa planetary "swing-by", as the manoeuvre is called, has never missed its target beyond an acceptable range.

Galileo was here

Cassini will send a probe on to the surface of Saturn's largest moon, Titan
The Galileo spacecraft flew by Earth twice on its way to Jupiter.

In 1990, it flew within 952km (592 miles) of the surface and was within eight kilometres (five miles) of total accuracy. And in 1992, it flew as close as 300km (189 miles) and came within a kilometre of total accuracy.

Launched two years ago, the $3.4bn Cassini probe is expected to reach Saturn in 2004 when it will photograph the giant planet's rings, atmosphere, and moons.

It will also deploy a sub-probe to study Saturn's largest moon, Titan.

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