Human ingenuity does not really have limits when a big goal is set. We wanted to lift ourselves off the ground and fly around the Earth, and we did it. We wanted to go to the moon, and we did it. Then at some point we wanted to go on a comet, orbit around, drop a lander and collect information with a detail never seen before. And guess what? We did it.
Rosetta, this is the name of the historic ESA mission that brought for the first time an object built by man to orbit around a comet. The origin of this mission dates back to 1985, when in the context of Horizon 2000, it was established that one of the main objectives would be to arrive on a comet, collect samples on the spot and bring them back to Earth. Both NASA and ESA went to work, independently, on the development of the mission, based in both cases on the Marineer Mark II project to save a little on the tight budget available. Budget that, unfortunately, slowed down NASA as early as 1992 and that led ESA the following year to rethink the mission from scratch. It was then opted for a probe able to reach a comet and a lander, to carry out the analysis on the spot, because bringing the samples back to Earth would have cost too much.
That’s how the mission went ahead, and the 46P/Wirtanen comet was chosen as the target that the Rosetta spacecraft was supposed to reach in 2011. However, two Ariane rocket failures postponed the launch until March 2, 2004, and the chosen target it was changed in favor of the comet 67P/Churyumov-Gerasimenko.
Finally Rosetta was traveling, along with Philae, the lander who would have the daunting task of landing on the surface of the comet. Now we had to do nothing but wait: in fact, to contain the amount of propellant to be consumed, the probe was placed in a trajectory such as to pass near Mars once and close to the Earth three times, in order to receive an acceleration. This maneuver, also known as gravitational assist, makes it possible to exploit the gravity of the planets to change trajectory and give an acceleration to the space probes. Thanks to this technique, for example, the Voyager 2 probe was able to reach Uranus and Neptune.
The first close flyby with the Earth took place on March 4, 2005. Two years later, on February 25, 2007, the probe carried out the gravitational assist maneuver with Mars, passing only 250 km away. On November 13, 2007, Rosetta made her second close pass around the Earth at a distance of about 5,700 km. During its travel, Rosetta also closely met two asteroids, 2867 Šteins and 21 Lutetia. The latter belongs to the asteroid belt and this meeting has made Rosetta the first European probe to reach this type of object.
During the month of August 2014, after ten years of travel in the solar system, Rosetta began a series of approaching orbital maneuvers using an integrated system of propellers. The probe was placed on triangular trajectories in order to progressively reduce the speed of the probe and the distance from the comet. On September 10, finally, the final maneuvers began and went into orbit around the comet 67P/Churyumov-Gerasimenko.
It was made, for now. Ten years of travel, some technical problems, corrections of course calculated with incredible precision. He could go wrong with everything, but it was not like that. And the Rosetta probe, became the first object built by man to orbit around a comet and to show us, finally, close, these fascinating celestial bodies.
In the next article, we will discover the next phases of the Rosetta mission, the landing of the Philae lander and the incredible scientific results obtained by Rosetta.