Philae

During my ongoing literature review I often discover interesting facts about things I’ve never thought about. Sometimes I can connect these facts with my own observations: The result is mostly a completely new idea why things are as they are. Maybe these ideas are new to you, too. Therefore I’ll share my new science based knowledge with you!

This week: This time, I think about the successful landing of Philae on Comet 67P/Churyumov-Gerasimenko on November 12th, 2014.

Wednesday afternoon was a very exciting time for spaceflight, science and mankind. All the tension evolved around the small robotic lander „Philae“ which was descending towards the surface of the comet 67P/Churyumov-Gerasimenko. Around 09:03 GMT the Lander Control Center (LCC) received the data that the lander was released from the mothership „Rosetta“. After the separation, the lander started its descent towards the icy and rocky surface of the comet in order to land there after a seven hours flight.

A few hours after the separation, the first pictures of the two spacecrafts arrived at the LCC.[1] Rosetta took several pictures of the descending lander with its landing gear and instrument booms extended. At this point the lander was still in the middle of its slow descend towards the surface of comet 67P. The tension reached its climax around 16:00 GMT or about seven hours after the spacecraft separation. All the scientists and misson controllers were waiting for the confirmation of a successful landing.

Finally, at 16:03 GMT the signal with the great news about the successful landing arrived at the LCC. Philae managed to land on the surface of the comet Churyumov-Gerasimenko. However, the data were a bit different than expected and indicated a rotation of the lander. The lander was equipped with some harpoons and some anchors in order to attach the spacecraft to the surface of the comet due to the weak gravity. Unfortunately, the harpoons were not fired and it turned out that the lander bounced up into space once again after the first landing. The lander reached an altitude of about 1km during its second flight and bounced up a second time after a second landing. Finally, after the third landing on comet 67P the lander remained on the surface. Mission accomplished![2]

The lander Philae is only able to communicate with the LCC when the mothership is flying over the landing site and is acting as a relay. The signal then needs about 30 minutes to reach the antennas on Earth. After several hours, the Rosetta spacecraft finally returned into the line of sight of Philae and the first observations, data and pictures were transmitted to Earth.

The first pictures from the surface of a comet were a huge success and an amazing result after the ten years flight of the Rosetta spacecraft out to the comet. Although it was just mind-blowing seeing these pictures, the pictures revealed a problem for the Philae mission as well. The third and final landing of the robotic lander ended in a spot that is surrounded by cliffs and rocks which are casting a large shadow on the solar panels of the lander. Moreover, the comet has currently a distance of about 3 AU to the Sun (the Earth has a distance of about 1 AU to the Sun). This distance reduces the light of the Sun by a significant degree and the solar panels are not as effective as they would be on Earth. The lander is equipped with two batteries which are able to supply the lander with electricity for about 60 hours.

The lander continued with its research and transmitted more data to the Earth every time a communication with Rosetta was possible. After 60 hours on the surface of the commet, the batteries were almost depleted and the lander was transmitting the last set of data back home. Afterwards, the lander switched to hibernation and began to sleep on the surface of Comet-67P. However, this does not necessarily mean the end of the Philae mission. The comet is currently flying towards the Sun and over time, the electricity generated by the solar panels will increase and maybe it is possible for Philae to wake up once again.[3]

The whole landing on the comet was a very ambitious mission and it were very exciting last days following the results and the activities of this mission. Congratulations to everyone who was involved in this spectacular mission!