Help! I woke up 800 million km from home

Imagine going to sleep one night and when you wake up you are 800 million km from home. This happened to the comet-hunting Rosetta spacecraft this week after nearly three years of hibernation.

Rosetta was built by the European Space Agency and launched in 2004. It has been busy: It passed close to the Earth three times, in 2005, 2007 and 2009, and it had close encounters with Mars (2007) and two large asteroids (2008 and 2010). But its main mission is to study a comet called 67P/Churyumov–Gerasimenko.

WAKE UP! You've got work to do.
A computer generated image of the Rosetta. Public Domain image

The aim is to be the first spacecraft to orbit the nucleus (main body) of a comet and the first to land a robot on the surface of a comet.

A computer generated image of the lander on the comet. Image supplied.

In June 2011 Rosetta went to sleep. To save energy on the long trip out to the comet, most of Rosetta's instruments and communications equipment were shut off. This is called 'Deep Space Hibernation Mode' or DSHM.

And then this week, 31 months later, everyone at the European Space Agency was delighted when Rosetta powered up and sent a message home saying everything was OK.

The plan is for Rosetta to meet up with the comet in August and then in November drop a robot onto its surface. Rosetta will then continue to orbit the comet for a year as it travels around the sun.

They want to use this mission to better understand comets and to find out more about how the solar system was created.

When Rosetta phoned home, it's signal was picked up by two satellite dishes in Australia, one in Canberra and one in Western Australia. The European Space Agency has dishes in Australia because Europe is pointing at the wrong part of the sky to communicate with Rosetta. It is similar to what happened during the moon landing in 1969, when satellite dishes in Australia were used to communicate with the astronauts as they landed on the moon.

One of the Aussie dishes that spoke to Rosetta. Image supplied.

Dishy Links

• The movie The Dish is all about Australia's role in the moon landing.
• In 2007, a group of scientists saw Rosetta in their telescopes and thought that it was an asteroid that was heading for Earth. Wikipedia has the story.
• Another comet recently flew around the Sun, but it got a bit too close.