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Cassini set to zip through Saturn rings

Cassini orbit insertion

An artist's impression of Cassini's insertion into Saturn's orbit (Image: NASA)

NASA's deep-space tracking station in Australia will be keeping a giant ear out this week as the Cassini spacecraft flies through Saturn's rings to insert itself into the planet's orbit.

After seven long years, Cassini will reach Saturn on Thursday, 1 July, 11:12 AEST (01:12 UTC) to begin its closest encounter yet with the ringed planet.

But we will not know about the event until 12:36 AEST (02:36 UTC) as the signal takes an hour and half to travel the nearly 1.5 billion kilometres to Earth.

Scientists at the NASA Jet Propulsion Laboratory in Pasadena will wait as the Canberra Deep Space Communication Complex (CDSCC) at Tidbinbilla, 35 kilometres south-west of Canberra, relays confirmation signals from the spacecraft to them.

"For seven years we've been tracking the Cassini spacecraft as it hurtles towards Saturn," CDSCC spokesperson Glen Nagle told ABC Science Online. "If we're not here, nobody finds out about what's going on out there."

Cassini will approach Saturn from beneath and plunge at 80,000 kilometres per hour towards the planet at a sharp angle. It will travel through the two outermost rings, named F and G, which are 2500 kilometres apart.

Once above the ring plane, Cassini's engines will reverse thrust for a scheduled 96 minutes to slow down the spacecraft, allowing it to be captured by Saturn's gravity and pulled into orbit. This orbit insertion burn is expected to be completed by 12:48 AEST (02:48 UTC), or by the time the signal reaches Earth, 14:15 AEST (04:15 UTC).

"If the engines don't fly we'll just fly right on past," said Nagle. "So this is a critical moment for this mission after seven years."

Cassini will then begin a four-year period of large elliptical orbits around Saturn, taking it past some of its moons. "It's a bit like a spirograph," said Nagle.

But the spacecraft will never again come as close to Saturn as it is expected to during its orbit insertion burn, within 20,000 kilometres.

Before the Cassini mission, Nagle said scientists had only ever had a "fleeting glimpse" of Saturn as the Voyager mission flew past in the 1980s.

"The role of the Deep Space Tracking Station will be to link our 70-metre and two 34-metre antennas into an array providing one big ear to listen in for this tiny signal coming from this spacecraft," said Nagle.

The signal from the joint NASA, European Space Agency and Italian Space Agency Cassini mission will be relayed to the Jet Propulsion Laboratory scientists who will then confirm whether the spacecraft has safely inserted into Saturn's orbit.

"Usually the first time we know that things are going well is by actually seeing the reaction of scientists at mission control at Jet Propulsion Labs that are on the live TV feed," said Nagle.

"We have a little thing here called the glee meter," he said. "When we see them happy, jumping up and down and cheering and hugging and kissing, we know we've done a good job and things have gone well. If they're looking sad, things have got bad."

Cassini beams back to Tidbinbilla radio signals packed with digital data from on-board scientific instruments and computer systems.

The key questions the mission is investigating are the composition of Saturn, its rings and its moons, how the planet was formed and why it has rings.

Tags: astronomy-space, computers-and-technology