Watching the comet chaser


Launched six years ago with the goal of visiting a comet and dropping a lander on its surface, the Rosettasatellite is finally preparing for a fly-by of one of its targets on Saturday

A CLOSE encounter of a remarkable kind takes place on Saturday when a European satellite millions of kilometres from home flashes past an asteroid. For two hours the Rosetta satellite will beam back a stream of pictures giving us our first glimpse of a space rock named Lutetia.

But this feat is only a prelude to an even more demanding challenge when Rosetta continues on its journey for a rendezvous with a comet in 2014. Once there, scientists hope to drop a lander onto the comet’s surface, an amazing accomplishment provided everything works to plan.

This will be our first look at the asteroid, which appears as no more than a dot of light through our most powerful Earthbound telescopes. Rosetta’s controllers will flip on the cameras and send back two hours of live footage, finally putting a “face” on this piece of rock.

Scientists believe that Lutitia is a bit like a giant potato, with a diameter of about 134km and an elongated shape. At its closest point, Rosetta will be less than 3,200km from Lutetia, the minimum distance that would allow the satellite to keep the entire asteroid in its camera’s field of view.

The European Space Agency controllers also hope that the fly-by will deliver important information about Lutitia’s composition.

The astronomers can’t make up their minds about Lutitia’s origins because of conflicting information. Either Lutitia is a C-type asteroid, a leftover bit of space rock that did not get mopped up by planets when the solar system formed, or it is an M-type asteroid. These are much more interesting to astronomers because they have metal on their surfaces. If significant amounts of metal are present then Lutitia must certainly be a fragment from a much larger asteroid, shattered to pieces by collisions in the asteroid belt beyond Mars.

It is no small thing to get a working satellite into position to make such observations, but this segment of the mission will seem as child’s play by 2014 when Lutitia really goes into action. Launched in March 2004, it is travelling a half a billion kilometres to meet up with a comet 67P/Churyumov-Gerasimenko – a full 10 years after the satellite was sent on its way.

The distances are so great that Rosetta will be put into deep hibernation during 2012 through 2013 to keep demands on it to a minimum. Then by July 2014 the satellite will be slowed allowing it to drop into orbit around the comet where it will stream back pictures and map the surface.

All the time Rosetta will be searching for useful landing sites for its piggy-backed cargo, the Philae lander. By September Rosetta will move into an even closer orbit and them on November 20th, 2014, Philae will be released and sent to drop softly onto the comet’s surface.

The lander will be fitted with a spike and hooks so it can fix itself down before sending back never before seen results about the comet’s composition.

Comets have been likened to “dirty snowballs”, water, rock, dust and carbon compounds that were left over after the formation of the planets. Yet some theorists also believe that cometary collisions delivered at least some of the abundance of water that covers our planet today.

The handlers at the European Space Operations Centre in Darmstadt, Germany, liken the depositing of Philae on the 5kmdiameter comet to dropping a pinhead onto the surface of a small coin in Berlin from Paris.

The lander will conduct experiments on the surface for at least five days, relaying data up to the orbiter for relay back to Earth. We won’t have to wait long however for the first images of Lutitia, which should reach Darmstadt some time before 11pm Irish time on Saturday.


AN IRISH company has played a crucial role in ensuring that the Rosetta mission to visit a comet will deliver spectacular pictures and unique data.Captec, of Malahide, Co Dublin, won two important contracts for Rosetta and its lander Philae, explains managing director Fred Kennedy. The company worked directly for the European Space Agency’s research centre to develop the satellite’s “electrical support system”.

Despite its rather unassuming name, the system manages the vital communications links between the lander Philae and the Rosetta orbiter – and between the orbiter and controllers on Earth.

“It manages the data interface,” says Kennedy. Without it Rosetta would not be able to collect and relay data coming from the surface.

Captec won a second Rosetta contract with main contractor Astrium to conduct an independent software validation check.

Captec tested all of the software onboard the satellite to ensure “it did what the prime contractor wanted it to do,” says Kennedy.

Another company with a long history of winning ESA contracts is Space Technology Ireland. Founded by Susan McKenna-Lawlor while professor of physics at NUI Maynooth, her company was also involved in early work on the electrical support system for the Rosetta mission.