The Rosetta Space Probe was designed to target the comet Churyumov-Gerasimenko, with launch on February 26, 2004 and rendezvous in 2014. The larger mass and the resulting increased impact velocity made modification of the landing gear necessary. After two cancelled launch attempts, Rosetta was launched on March 2, 2004 at 7:17GMT. Besides the changes made to launch time and target, the mission profile remains almost identical.
The first flyby of Earth occurred on March 4, 2005.
On February 25, 2007, the craft was scheduled for a low-altitude bypass of Mars, to correct the trajectory after the first launch in 2003 was delayed by one year. This was not without risk, as the estimated altitude of the flyover manoeuvre was a mere 250 km (155 miles). During that encounter the solar panels could not be used since the craft was in the planet’s shadow, where it would not receive any solar light for 15 minutes, causing a dangerous shortage of power. The craft was therefore put into standby mode, with no possibility to communicate, flying on batteries that were originally not designed for this task.This Mars manœuvre was therefore nicknamed “The Billion Dollar Gamble”.Fortunately, the flyby was successful and the mission continued as planned.
The second Earth flyby occurred on November 13, 2007.
The spacecraft performed a close flyby of asteroid 2867 Šteins on September 5, 2008. Its onboard cameras were used to fine-tune the trajectory, achieving a minimum separation of less than 800 km (497 miles). Onboard instruments measured the asteroid from August 4 to September 10. Maximum relative speed between the 2 objects during the flyby was 8.6 km/s (19,240 mph)
Rosetta’s third and final flyby of Earth happened on November 12, 2009.
The asteroid’s orbit was known before Rosetta’s launch, from ground-based measurements, to an accuracy of approximately 100 km. Information gathered by the onboard cameras beginning at a distance of 24 million km will be processed at ESA’s Operation Center to refine the asteroid’s position in its orbit to a few km.
In May 2014, the Rosetta craft will enter a slow orbit around the comet and gradually slow down in preparation for releasing a lander that will make contact with the comet itself. The lander, named “Philae”, will approach Churyumov-Gerasimenko at relative speed around 1 m/s and on contact with the surface, two harpoons will be fired into the comet to prevent the lander from bouncing off. Additional drills are used to further secure the lander on the comet.
Once attached to the comet, expected to take place in November 2014, the lander will begin its science mission:
- Characterisation of the nucleus
- Determination of the chemical compounds present, including enantiomers
- Study of comet activities and developments over time
The exact surface layout of the comet is currently unknown and the orbiter has been built to map this before detaching the lander. It is anticipated that a suitable landing site can be found, although few specific details exist regarding the surface.
With thanks to Phil Krause & wikipedia