Dutch astrophysicist Dr Fred Jansen is no stranger to the difficulties of space exploration. He led the team that put an X-ray observatory in orbit in the 1990s, and has since overseen exploration operations to Mars and Venus. But the Rosetta mission manager described his latest challenge as the most difficult yet.

On Wednesday, the European Space Agency will try to do the equivalent of transferring an object from one speeding bullet to another. More than 500m km away from Earth, between Jupiter and Mars, a probe named the Philae lander will be ejected from the Rosetta spacecraft and land on a comet for the first time in scientific history.

“The comet and Rosetta are flying through space at 60,000km an hour,” said Dr Jansen, “In many, many aspects this is an absolute first.”

Previous missions to planets like Mars have been far less complex, said Dr Jansen, as ESA has already known about the objects, their densities and their atmospheres.

“With Rosetta this wasn’t the case,” he said, “It’s like the mission impossible because you are trying to achieve something at an object, where you don’t know what the object is like.”

Even the unusual double-lobed shape of comet 67P/Churyumov-Gerasimenko was not discovered until the orbiter returned images earlier this year.

Since its launch in 2004, ESA has used the gravity of Earth and Mars like a slingshot to accelerate the orbiter into the comet’s trajectory. In August, Rosetta became the first spacecraft to orbit a comet – but the mission faces further trials.

“The main difficulty in putting the lander on the comet is that the lander is passive”, said Dr Jansen. Once released, it will drift independently onto a landing ellipse as wide as 500m… see more

source: independent UK