Despite Glitch, European Spacecraft's Asteroid Flyby a Success
The 5-km wide Asteroid Steins seen from a distance of 800 km, taken from two different perspectives. At the top of the asteroid (as shown in this image), a large crater, approximately 1.5-km in size, can be seen. Scientists were amazed that the asteroid survived the impact that was responsible for the crater.
Credit: ESA ©2008 MPS for OSIRIS Team.

PARIS - Europe's Rosetta comet-chaser satellite successfully detoured to take a look at a rare type of asteroid Friday, getting a close-up view of the diamond-shaped Steins asteroid, a gray, 3-mile (5-km) wide rock that appears in images as a pock-marked with multiple craters that ultimately will help determine its age.

The European Space Agency (ESA) probe?s narrow-angle camera apparently switched off as it closed in on the asteroid Steins, but the photo survey was ultimately ?a sideline? mission to the actual flyby and another camera worked perfectly, ESA officials said in a post-flyby briefing early Saturday at the agency?s ESOC space operations center in Darmstadt, Germany.

"We were very conservative, perhaps too conservative," said Uwe Keller, principal investigator for Rosetta's OSIRIS camera, adding that the tool was put into safe mode and was not damaged.

"Steins looks like a diamond in the sky," Keller added.

The billion-dollar Rosetta satellite, carrying a small instrument package on a lander that will attempt to land on a comet in 2014, came to within 500 miles (800 km) of Steins as it hurtled through space at about?223 million miles (360 million km) from Earth.

Fifteen instruments were trained on Steins. Much of the data will be delivered in the coming weeks, but Rosetta mission managers said Saturday that they have already downloaded enough data to say the flyby was a success.

?This was a very big test of the waters" for Rosetta, which was launched in March 2004, said David Soutwood, director of science and robotic exploration at the European Space Agency (ESA). "Three hundred and sixty million kilometers is not just down the street. It is the first big step toward our grand exploration of asteroids and comets. They're small but important. Our solar system grew out of things like this. "

One of the flyby?s most challenging aspects of the flyby was what ESA officials called a "flip" maneuver in which the satellite changed its attitude by 180 degrees for a brief period during the approach.

Andrea Accomazzo, Rosetta spacecraft operations manager, said the maneuver, and the brief exposure of the temperature-sensitive underside of Rosetta to the sun, "stretched the limits" of what ground teams felt they could do to accommodate scientists' desire to see Steins in full sunlight, from as close a distance as possible.

Satellite operations managers and Rosetta scientists eventually agreed that 500 miles (800 km) was as close as the satellite would be allowed to Steins.

Mission managers hope that an analysis of the flyby data that will be arriving in the next few weeks will permit them to estimate Steins' age, in part from an examination of the many craters on its surface.

Rosetta's principal mission is to take a close examination, in 2014, of the comet 67/P Churyumov-Gerasimenko, and ultimately to send its small Philae lander to the comet's surface, where it will attempt to use a spear-like system to attach itself to the comet. But before reaching the comet, Rosetta is due to swing past another asteroid - the space rock Lutetia - in June 2010.

"It looks like a typical asteroid, but it is really fascinating how much we can learn from just the images,? ESA?s Rosetta mission manager Gerhard Schwehm said of Steins. ?This is our first science highlight; we certainly have a lot of promising science ahead of us. I?m already looking forward to encountering our next diamond in the sky, the much bigger Lutetia."

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