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Rosetta Space Probe, Rendezvous with a Comet

On the 2nd March 2004, the european space agency launched the Rosetta Space Probe using an Ariane 5 space rocket. The object of the mission was to study a comet and learn more about its composition and even our origins as to whether we came from comets. The theory that we hitch-hiked to this planet is called Panspermia. The comet that would ultimately be the target was P67/Churyumov-Gerasimenko. The probe would be two parts, a lander craft named Philae and an orbiter called Rosetta.

The project had originally been conceived as a joint project with national aeronautics and space administration (n.a.s.a.), the United States space agency but NASA pulled out due to budgetary constraints. The original plan had seen both teams collaborate on the same design and thus minimise costs. However, rather than cancel the project, ESA decided to carry on with the project and Rosetta was born. The name Rosetta comes from the Rosetta Stone which was discovered by Pierre-Francois Bouchard, a Napoleonic soldier in 1799. 1. The stone carried a decree issued in 196 B.C. in the city of Memphis (Not Memphis, Tennessee) by King Ptolemy IV. The Rosetta Stone is most widely remembered for helping to understand Egyptian Hieroglyphics.

Rosetta had been designed and built to encounter the P46/Wirtanen comet but because of problems with the launch vehicle, that plan had to be scrapped and Churyumov-Gerasimenko was chosen instead for the mission. The original plan had been for a rendezvous in 2011 but because of the change in chosen comet, the encounter would now take place three years later than had been originally scheduled. The pictures below are artists impressions of the probe and lander (the lander picture altered to fit the page).

The Rosetta Space Probe (Copyright ESA)

To get into orbit round the target, Rosetta had to do a number of orbits round the Sun that would see it cross the path of Earth. and take it out past Mars and then onto Jupiter. The reason for the slingshot affect is to build momentum and to reduce the amount of fuel that is needed to get to the rendezvous. Anyone can tell you the quickest time is a straight line to an object but its not always the most efficient which is why the slingshot effect is used. The craft uses the gravity of space bodies to propel it through space. On the ESA website is a very good animation which shows the route that Rosetta and the comet would take until Rosetta catches up with the comet. A word of advice, don't take the default view as being fixed, you can use the mouse wheel to pull back out and see more. The below is a picture showing the full path of Rosetta (Red) and the Comet (Blue). The site is worth seeing for a break down of the journeys.

Path of Comet Churyumov-Gerasimenko and Rosetta (Copyright ESA)

Churyumov-Gerasimenko is a short term comet, it orbits the Sun every 6.5 years compared to long term comets which can take thousands or years which we will never see again. The comet was first discovered in 1969 by Soviet astronomers Klim Churyumov and Svetlana Gerasimenko. Unfortunately, it is not a visible comet like Halley's Comet or Hale-Bopp but nonetheless, the target is perfect for the operation at hand. The below picture shows the size of the comet compared to London.

Comet Churyumov-Gerasimenko compared to London (copyright ESA)

The first approach at the Comet was to take place about January - May of 2014 when the probe was awoken and instructed to slow down its approach to the comet. The next phase was to take place in August of the year when the probe was less than 200 kilometres from the nucleus. The probe was to get closer to the nucleus to prepare for the eventually launch of Philae, a small landing object which would hook itself onto the rock and carry out experiments.

The separation and eventually landing took place, the lander, a small box like object landed succesfully. That was the good news but it soon became clear that the lander had landed in a dark spot on the comet and its battery power was not being replenished. The lander was powered by solar power and although the batteries were full at landing, it wasn't going to be topped up. Scientists took the decision to carry out as many operations as they could before the batteries went dead. The lander could come back in May the following year when the comet rotates and the batteries are charged again 2. All the main experiments were carried out before the batteries went dead.

When Rosetta caught up with the comet, it was able to take photos of the surface of the comet. You will notice that they are not white but a dirty grey. The comet also appears as grey in a colour photo. As the comet is not that close to the Sun, there is no trail.

Comet Churyumov-Gerasimenko Surface (copyright ESA)

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