The European Space Agency (ESA) probe Rosetta is on a ten year journey to visit the comet Churyumov-Gerasimenko. Launched on 2nd March 2004, it will finally arrive at its target in May 2014. Once there, Rosetta will place a lander, called Philae, on the comet. Rosetta will then orbit around Churyumov-Gerasimenko, following it for approximately 18 months. Rosetta is the first ever mission to orbit around and land on a comet. The data that we will receive from both the lander and orbiter will hopefully tell us more about the early solar system, since comets contain some of the oldest material in the solar system.


The reason for this long 10 year journey is that Rosetta’s orbit around the Sun must be matched with the orbit of the comet. Like all comets, Churyumov-Gerasimenko orbits around the Sun in an elliptical (oval shaped) orbit. It swings in towards the Sun, just closer than Mars, and then out again beyond Jupiter, every 6.6 years. At the moment, there is no rocket powerful enough to put the probe into this orbit directly. Instead, we rely on another method called ‘gravity assist slingshots’.
 

Rosetta has made several close fly-bys of planets. Each one uses the force of gravity from the planet to speed up the probe and sling it out again into space. The vast majority of space missions use these gravity assist slingshots; they are a way of accelerating spacecraft for free, since no fuel is used up. Rosetta has done three slingshots already; the first was past Earth in March 2005, then Mars in February 2007, followed by Earth again in November 2007. It’s due to complete the fourth and final slingshot around Earth on November 13th 2009 at 7.45 GMT, flying almost 2,500 km above the surface. Every one of the slingshots must be calculated accurately. The onboard guidance system will be working hard to make sure Rosetta is on the correct course, as will the mission controllers back on Earth.


Another thing we will be looking for is a rather strange effect that sometimes seems to occur during gravity slingshots. Some probes get sped up slightly more than expected. Rosetta’s first Earth fly-by increased the speed by 1.8 millimetres per second more than predicted. This is a tiny amount, but we have no idea at the moment what causes it!

Thanks to ESA and New Scientist

 
For more information, visit the official ESA Rosetta site: http://www.esa.int/SPECIALS/Rosetta/index.html

Rosetta makes final Earth fly-by