The incredible journey of the Rosetta probe

The history of Europe’s Rosetta probe is hectic. After the principle of a comet mission was officially adopted by the European Space Agency, the agency initially envisaged a collection of cometary samples, but this project seemed technologically risky (in fact it was only in 1999 that NASA launched Stardust). In 1994, the ESA opted for a probe accompanying a comet, with two landers deposited on its nucleus, one provided by Germany and the other one by France and NASA. After NASA dropped out of the project, only a single lander remained, named Philae, while the orbiter around the comet was Rosetta, named for the famous stone that helped archaeologists to decipher Egyptian hieroglyphics. Rosetta was supposed to reach comet 46P/Wirtanen, a very active comet, with the hope that the dust flow would not damage the probe. The launch was scheduled for the beginning of 2003 by an Ariane 5 rocket. However, on December 11, 2002, an Ariane 5 rocket exploded on launch. Thus the schedule was upset and it was clearly impossible to reach the planned comet. Another target had to be chosen. This was comet 67P/Churyumov-Gerasimenko, discovered in 1969 by two Ukrainian astronomers. The celestial mechanics calculations defining the trajectory of the probe to reach the comet had to be redone.

L’incroyable périple de la sonde Rosetta - 1

Lancement de Rosetta à Kourou (Guyane) par une fusée Ariane 5, le 2 mars 2004

Crédit : ESA/CNES/ARIANESPACE-Service Optique CSG, 2004

Rosetta was successfully launched by an Ariane 5G+ on March 2, 2004. The trajectory of the probe was very complex, because it was not easy to reach and to accompany with little fuel a comet whose orbit was very different from that of Earth. This required several passages near planets that accelerated the probe and diverted its path. This is what experts call the gravitational assistance. After a first passage near the Earth, a Mars flyby and two flybys near the Earth, and consuming a ton of fuel, the probe finally reached the comet 10 years after the launch, a great success for celestial mechanics.

During its journey, Rosetta passed near two asteroids, Steins and Lutetia, of which beautiful images were obtained. Then the probe began to hibernate on June 8, 2011. Its awakening — a critical time — took place on January 20, 2014.






L’incroyable périple de la sonde Rosetta - 2

La trajectoire de Rosetta. La sonde a subi une première déviation (assistance gravitationnelle) par la Terre, puis une par Mars, puis encore deux autres par la Terre, afin de rejoindre la comète 67P et de l’accompagner sur sa trajectoire.

Crédit : ESA

The mass of the comet being relatively small, it was virtually impossible for Rosetta to orbit freely around it immediately. With the small jet engines it contained, it was made to maneuver in triangles around the nucleus. Only at a later stage was the probe close enough to the nucleus to orbit around it. Even then, its course had to be corrected frequently to send it away from the nucleus rapidly enough to prevent damage by the dust the comet ejected.

Crédit : ESA – C. Carreau