Part II. The Rosetta Mission 9

(10) One of the most ambitious projects of cometary exploration was the Rosetta mission. It established a series of firsts; it was: the first spacecraft ever planned that will have to go into orbit around a comet; the first to observe the changes in comet activity, the first to carry a small Lander that will descend onto a comet's icy nucleus to determine its properties. The prime scientific objectives are to study the origin of comets, the relationship between cometary and interstellar material and its implications with regard to the Solar System. (line 67)

(11) Rosetta is a robotic spacecraft of the European Space Agency (ESA) on a mission to study comets. It consists of two main elements: the Rosetta space probe and the Philae Lander. Both the probe and the Lander carry a large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted. (line 71)

(12) Rosetta was set to be launched on January 12, 2003 to rendezvous with the comet 46P/Wirtanen in 2011. However, this plan was abandoned after a failure of the planned launch vehicle Ariane 5 on December 11, 2002. A new plan was formed to target the comet 67P/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 7:17 GMT. Besides the changes made to launch time and target, the mission profile remains almost identical. (line 79)

(13) Rosetta is scheduled to arrive at Comet by mid 2014 and go into its orbit. It will collect detailed information about comet nucleus and its environment and it will survey it, seeking a suitable landing site, once that is selected, the Rosetta Lander will separate from the spacecraft and slowly descend a few kilometers to the surface of the icy nucleus. It is expected that the data gathered by the Lander (close-up pictures, samples of the primordial ices and gases, and probes below the surface of the "cosmic iceball") will greatly change our understanding of comets. But even more exciting for some scientists is what the data will reveal about the most primitive building blocks of the Solar System. (line 87)

(14) To gain enough orbit energy to reach its target, one Mars and two Earth gravity assists¹¹ will be required. It will take the spacecraft eight years to reach the comet. The long mission duration requires that there be extended hibernation periods. On route, it will pass close to two asteroids, Šteins and Lutetia, and gather information about them as well. (line 91)

(15) The spacecraft has already performed two successful asteroid flyby missions on its way to the comet. In 2007, Rosetta performed a Mars swing-by (flyby), and returned images. The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010, and is presently in "hibernation" mode and on-target for its final destination. The spacecraft will remain in this state until 20 January 2014 when the hibernation exit sequence will be initiated. (line 97)

(16) If this project succeeds, then we will probably know just about everything there is to know about comets. Our scientific knowledge will be gained at the expense of the mystery, myth, and conjecture that mankind has projected onto these exciting heavenly bodies, these volatile travellers in space. We will also know a lot more about the universe in its earlier stages of formation. (line 102)

This is the planned timeline for the mission after its launch:

• First Earth flyby (March 4, 2005)

• Mars flyby (February 25, 2007)

• Second Earth flyby (November 13, 2007 )

• Flyby of asteroid 2867 Šteins (September 5, 2008)

• Third Earth flyby (November 13, 2009)

• Flyby of asteroid 21 Lutetia (July 10, 2010)

• Deep-space hibernation (June 2011 - January 2014)

• Comet approach (January–May 2014)

• Comet mapping / Characterisation (August 2014)

• Landing on the comet (November 2014)

• Escorting the comet around the Sun (November 2014 - December 2015)

• End of mission (December 2015)

Rosetta's current location can be found on the ESA website.^[7]