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.