On September 5, the Rosetta spacecraft detected its lost lander Philae, wedged in a dark corner of comet 67P-Churyumov-Gerasimenko, according to European Space Agency reports. From the time it reached the side of the comet just over two years ago, the spacecraft has been diligently observing its subject and sending home reports. The report on finding Philae will be among its last ones, with its mission set to come to a close at the end of this month.
This has been on the cards since Philae ceased communicating with the spacecraft in July last year. Since then, Rosetta, apart from itself observing the comet, has made several excursions to try and see if Philae would wake up and become operable. But that has not happened.
Also, now, as the comet moves on further and further from the sun, the amount of solar energy the spacecraft will get will decline. Rather than let it hibernate and take a chance that it will remain operable until it is close to the sun once again, the team has decided to end its mission on September 30.
In its final stages, the spacecraft will make a few elliptical orbits around the comet and land on it to rest.
It has been a long association for the team members with the mission. It has lasted for over two decades.
The International Rosetta Mission was approved in November 1993, and it took nearly a decade for the launch (in March, 2004). Having decided that they wanted to build a comet chaser, ESA’s first chosen target was Comet 46 P-Wirtanen, which is also a short period comet, having an orbital period of 5.4 years. However, mission delays meant that it could not be reached comfortably and so the ESA chose to pursue Comet 67P-Churymov-Gerasimenko instead.
There was no rocket powerful enough to launch the spacecraft directly from the earth to the vicinity of the comet. Instead the comet was first launched into a parking orbit and then sent on its way to the outer solar system. During its course, the Rosetta spacecraft underwent multiple flybys near the earth and Jupiter, where it took advantage of what is called a gravitational “kick” to gain velocity from its close encounters with earth and Jupiter and move on to its comet.
A gravitational kick works like this: when the spacecraft flies by a massive planet like Jupiter which is swinging along its path, it gets dragged under this effect and “catapulted” into space at a much higher velocity. The mission members planned and executed this with accuracy.
Further, to limit usage of power during its long sojourn, the spacecraft was put into hibernation for much of its journey.
Communication with the spacecraft over these long distances was achieved through a radio link between the spacecraft and the earth station, which was how the station remotely controlled the instruments on the spacecraft.
The journey of Rosetta has been a long and exciting one – after ten years and traversing nearly 6.4 billion kilometres, looping around the solar system, before finally reaching the comet on August 6, 2014.
Given that it made the long and arduous journey as planned, its agenda was to rendezvous with the comet at a point where it was far from the sun. This also, it did successfully.
The comet reached, Rosetta planted the “lander” Philae on the comet for close observation. To the dismay of all concerned, Philae’s landing did not go as smoothly as planned and the lander fell into hibernation in November and stopped communicating with the spacecraft soon after it landed. It, however, “woke up” on 26 April 2015 and started sending signals in June, enriching and adding to our knowledge of comets.
Now, as calculated on September 2, Rosetta is 676,344,049 kilometres from the earth and moving further every minute, accompanying its comet where it will come to rest on September 30.
Source: The Hindu