Rosetta: Europe's Mission that landed on a Comet

Philae lander separating from Rosetta spacecraft. Credit: ESA

• Launch Date: March 2, 2004
• Launch Site: The European spaceport at Kourou, French Guiana
• Launch Vehicle: Ariane-5 G+
• Mission Type: Orbiter & Lander
• Targets: Šteins, Lutetia, and 67P/Churyumov-Gerasimenko
• Dimensions: 2.8 Meters by 2.1 Meters by 2.0 Meters (Orbiter)
• Mass: Orbiter was 3065 Kilograms (Including Propellant) & Lander was 100 Kilograms

You can build your own Philae lander out of LEGO here.

The Mission

Rosetta was a mission to investigate the origins of the solar system, and especially Earth's formation. To do this, it would visit a comet, and land a probe on the surface to analyze it. The mission is named after the famous Rosetta stone, the discovery of which lead to the first translations of ancient egyptian hieroglyphics. The Philae lander is named after a less famous egyptian obelisk that served a similar purpose. The mission's original target was comet 46P/Wirtanen, but this was changed to 67P because of mission delays. It launched on Europe's heavy lift workhorse rocket: The Ariane 5, on March 2, 2004. 

Rosetta's Journey. Credit: ESA

Rosetta made a gravity assist of Earth on March 4, 2005, then moved on to a gravity assist of Mars on Febuary 25, 2007. Rosetta tested many of its scientific instruments and cameras during the Mars assist, and then moved on for another flyby of Earth on November 13. Almost a year later, the spacecraft made a flyby of the asteroid Šteins, with a closest approach of 800 kilometres. 

A month later was the final Earth gravity assist, on November 12, 2009. Before it went on its journey to 67P, Rosetta made a flyby of another asteroid: Lutetia, on July 10, 2010. The spacecraft had an uneventful four years until it approached 67P in 2014. Rosetta performed eight burns to slow down its relative velocity, and get captured in the comet's puny gravitational field. Rosetta arrived at 67P on August 6, 2014.

The spacecraft had to make many complicated maneuvers in order to stay close to the comet. Rosetta then started mapping the comet, in order to find an ideal place to drop down the lander.

Various views of comet 67P from the Rosetta Spacecraft. Credit: ESA

The selected landing site was near the head of the comet, and named "Agilkia." Rosetta released Philae on November 12, 2014. The lander began its slow decent to the comet, at a speed of 1 meter a second. Philae touched down on the comet at 15:33 UTC, but then bounced off the surface because of a failure in the anchoring harpoons. 

The surface of the comet was softer than expected, and Philae bounced two more times before resting at a 30 degree angle in an area shadowed by a cliff. This was a big problem, because Philae relied on solar power, and the batteries would only last a few days. The scientist scrambled to collect enough data as possible in this short time. While they weren't able to complete Philae's primary mission, it still got plenty of good data.

Contact with Philae was briefly regained in mid july of 2015, when the shadowed region was illuminated by the Sun, allowing the lander to recharge. While they were able to contact the lander, no one knew exactly were on the comet it was. Later in September 2016, at the end of Rosetta's mission, the orbiter lowered its orbit to touch down on the comet. High resolution images showed the Philae lander, finally revealing its location.

The locaton of Philae on 67P. Credit: ESA

Rosetta has made many fascinating discoveries around 67P. It discovered that the isotope ratio of the comet's ices, differed from that in Earth's water. Amino acids such as glycine were found to be present in the comet. Rosetta and Philae also made many discoveries about the comet's atmosphere, and even its magnetic properties.
 

Infographic of Rosetta's accomplishments. Credit: ESA

The Targets

Image of Šteins from the Rosetta spacecraft. Credit: ESA

• Date Discovered: November 4, 1969
• Designation: 2867 Šteins (1969 VC)
• Class: Main-Belt Asteroid
• Radius: 2.58 Kilometres
• Rotational Period: 6.05 Hours
• Orbital Period: 1327.26 Days (3.63 Years)

Lutetia as seen by Rosetta at closest approach. Credit: ESA

• Date Discovered: November 15, 1852
• Designation: 21 Lutetia (A852 VA)
• Class: Main-Belt Asteroid
• Radius: 47.88 Kilometres
• Rotational Period: 8.17 Hours
• Orbital Period: 1388.49 Days (3.8 Years)

67P as seen by Rosetta on May 20, 2015. Credit: ESA

• Date Discovered: October 22, 1969
• Designation: 67P/Churyumov-Gerasimenko
• Class: Jupiter-Family Comet [NEO]
• Radius: 1.7 Kilometres
• Rotational Period: 12.76 Hours
• Orbital Period: 2353.08 Days (6.44 Years)