Philae Plays Hopscotch on Comet. Wins.

Philae is safely on the surface of Comet 67P, as these first two CIVA images confirm. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic. Image courtesy of ESA.

by Nur Hussein, staff writer

The European Space Agency (ESA) held a press conference this morning in Darmstadt, Germany, to discuss what they’ve learned about Philae’s historic landing on comet 67P yesterday. We now know that after yesterday’s harrowing landing, the lander is on the surface and operational, and the instruments have started to make their observations. Some data has already been sent back. However, the lander bounced twice after the initial touchdown, and it is somewhere on the comet other than where they intended, but not too far from “site B.” They cannot get an exact location fix yet. They also released some astounding photos. Klim Churyumov, one of the first observers of the comet (after whom it was named) was on-hand, and said he was very happy that the mission was successful, and congratulated the people involved for making the “miracle” possible.

Jean-Pierre Bibring, the principal investigator for the CIVA imager, explained what ESA knows about the Philae lander’s current location. Yesterday, the harpoon anchors failed to fire, as did the top thruster. Because of the lander’s landing bouce, they are unsure of the exact location of the lander, but it has already sent back photos and data from the instruments. Bibring described the lander’s position as “almost vertical.” Two of the lander’s feet are on the ground, but the other foot is not. Bibring showed multiple photos taken by the lander, which places it somewhere within the shadow of a cliff-like structure. He also explained that while they cannot yet confirm the nature of the comet’s crust, the rebound of the lander indicates a “higher strength material” than expected.

Red cross marks likely site of Philae’s first touchdown. OSIRIS narrow-angle image taken from a distance of 30 km on September 14, 2014 (prior to landing). Image courtesy of European Space Agency – ESA.

Stephan Ulamec, the Lander Manager at the Deutsches Zentrum fur Luft und Raumfahrt (DLR) German Aerospace Center, said that lander came in at about 1 meter a second, and rebounded at 38 meters a second. It made a jump that lasted 2 hours and travelled approximately 1 kilometer. It bounced back up again, a smaller bounce this time at 3 cm/s. It was up in space again for about 7 minutes before coming down. The first analysis by CONCERT (the radar tomographer that scanned through the nucleus) came through, allowing scientists to reconstruct where the lander is, by assuming certain properties of the comet. Yesterday evening, they lost contact with the lander when it dipped below the horizon from the orbiter, but re-established the link at 7:22 UTC this morning, when it came back round.

“An interesting thing is we did a lengthy landing site selection process, we weren’t sure about landing site J or I or B, maybe we landed on all three of them!” joked Ulamec.

The lander is still not anchored, but they need to be very careful in activating any mechanisms lest they make the situation worse. Ulamec added, “Can we optimize the position of the thing? There is such low gravity that … if you are clever enough, you can manipulate the position to something more favorable.”

Ulamec explained that some instruments such as the drill might pose a problem to use, due to the unknown landing orientation, but they do not yet want to dismiss any of the experiments. They’re hesitant to use any instruments that might set off the comet in motion, so they may attempt to run the experiments that don’t have the potential to dislodge the lander first, then try drilling afterward. Bibring added that the drill was an important core part of the mission, and they will try to test it step by step as soon as they can. The clock is ticking on the primary battery, so they’re racing to gather enough data to make a decision while there is still enough battery power left to run the drill experiments.

In red, the target landing site. In blue, the likely area in which Philae actually landed. Graphic courtesy of European Space Agency – ESA.

Koen Geurts, Lander Technical Manager at the DLR joined in via remote video feed from Lander Control Center (LCC) in Cologne, France. He described how they saw that the lander was still moving even after the first touchdown, so the know it bounced twice. The lander is now somewhat more occluded from the sun than was expected, so Philae is receiving less solar energy than planned; 1 and half hours instead of six or seven. This will affect their “energy budget” for the future as the lander relies on the sun for recharging during extended operations.

Rosetta Project Manager, Fred Jansen, explained that since there is a limited amount of battery power so they do not know how long they will operate the lander once the initial charge is used up. However, the Rosetta orbiter will continue for 20 months.

Stefano Mottola, principal investigator of the Rosetta Lander Imaging System (ROLIS), also contributed through the Cologne video feed. He shared some more breathtaking images from the mission. They had been very busy through the night, collecting and processing the images (this is still in progress). The images revealed that the comet surface is covered in dust and debris measuring from a few millimeters to a few meters across in size. Researchers hope to trace the origins of the detritus, and the distribution of the particles. The dust that covers the surface may be an indication of active processes at work on the comet.

View from the smaller of Comet 67P two lobes (foreground in lower left) over to the larger lobe. NAVCAM image captured from a distance of 9.7 km from the centre of the comet. Image courtesy of European Space Agency – ESA.

Ignacio Tanco, Deputy Spacecraft Operations Manager, ESA expressed his appreciation for his team and all the hard work they’ve put into the mission. He said he had “enormous professional gratification to have achieved this level of success.”

Holger Sierks, principal investigator for the OSIRIS cameras on board the orbiter had praise for operations and flight dynamics, whom he described as “heroes of this mission.” He said that when he first saw the initial photos of the lander just moments after separation, he was surprised to see it had the landing struts out, prepared to touch down “like a cat.” The OSIRIS team are working very hard analyzing images to visually locate Philae as soon as possible.

Andrea Accomazzo, Flight Operations Director said, “We are all tired, but it was a huge effort of a huge team. I want to mention some masterpieces of effort on this project. Flight dynamics, you are the best in the world, They deserve the image of the day … What we have ahead of us is a fantastic mission. We’ve flown this mission not for operations, but for science. We’re just starting this mission … we hope we’ll be talking about the science from this mission for years to come”


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About Nur Hussein

Nur is a tinkerer of programmable things, an apprentice in an ancient order of technomages. He enjoys fantasy, sci-fi, comic books, and Lego in his spare time. His favourite authors are Asimov and Tolkien. He also loves Celtic and American folk music. You can follow him on twitter: @nurhussein

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