The European Space Agency’s (ESA) Rosetta mission is only three days away from a close fly-by of the asteroid Lutetia. At more than 100km across, the oddly shaped body is something of a mystery to astronomers as they have not been able to determine its composition and structure. At about 15h45 UT this Saturday (Universal Time used to be called Greenwich Mean Time, back when children respected their elders, a loaf of bread cost 5 cents and the world was sepia tinted), Rosetta will pass Lutetia at a speed of about 15 kilometres per second and all of its science instruments will be working at full tilt to collect as much information as possible. The trajectory of the spacecraft has to be precisely controlled to ensure that the distance between the asteroid and Rosetta is just right – if it’s too close then the camera’s won’t be able to photograph the entire asteroid at once, but if it’s too far then they won’t pick up enough detail.
This flyby is just one part of Rosetta’s ten year mission: Launched in 2004, Rosetta has performed a number of gravitational assist manoeuvres to whip up enough speed to catch it’s primary target: Comet 67P/Churyumov-Gerasimenko. Currently it is navigating the Asteroid belt, and in May 2011 will enter a hibernation mode until 2014 when the comet passes nearby. For the next six months, Rosetta will perform braking manoeuvres to slow down and match speeds with the comet, gradually moving in towards the nucleus until it is eventually close enough to snap photographs, collect science data, and land.