Tag: Comet 67P/C-G

The magic of engineering: Using the seven images Philae snapped as it made its descent to Comet 67P/C-G, engineers have created a short movie simulating what the surface would have looked like as the lander descended.

I have posted the video below the fold. Be sure to go to the link above however to find out how this was done.
» Read more

Link here.

The story is fascinating because the lander’s behavior and response to commands has been quite puzzling. They have had about a half dozen short contacts of varying length, all interspersed with a lot of intermittencies. At the moment they have not entirely given up on Philae, since based on what they know of its location and condition it could remain functional through the end of this year. They also recognize that re-establishing contact is becoming increasingly unlikely. The big hope is that once the comet moves farther away from the sun and becomes less active, they will be able to move Rosetta in closer, when the chances of contact will improve.

The Rosetta science team today released all data obtained by the mission through Philae’s landing on November 14.

If you go here you can browse all the images the spacecraft’s high resolution camera took during that time period. You might even discover something the project scientists missed in their first perusal.

Cool image time! The Philae science team yesterday published in Science a set of papers describing their results from the lander’s approach and bouncing landing on Comet 67P/C-G.

Data were obtained during the lander’s seven-hour descent to its first touchdown at the Agilkia landing site, which then triggered the start of a sequence of predefined experiments. But shortly after touchdown, it became apparent that Philae had rebounded and so a number of measurements were carried out as the lander took flight for an additional two hours some 100 m above the comet, before finally landing at Abydos.

Some 80% of the first science sequence was completed in the 64 hours following separation before Philae fell into hibernation, with the unexpected bonus that data were ultimately collected at more than one location, allowing comparisons between the touchdown sites.

The images from lander so far released show the approach to the first site, with one boulder getting larger and larger as it descends, followed by images at the final landing site, showing a fractured, uneven, and very rough surface with the lander apparently sitting sideways with one foot off the ground.

An animation of the first touchdown, created by these images, can be viewed here.

Update: A good summary of the results can be read here.

Engineers on the Rosetta team are struggling to figure out why they cannot get a solid communications lock with their Philae lander, and have come up with several explanations.

One possible explanation being discussed at DLR’s Lander Control Center is that the position of Philae may have shifted slightly, perhaps by changing its orientation with respect to the surface in its current location. The lander is likely situated on uneven terrain, and even a slight change in its position – perhaps triggered by gas emission from the comet – could mean that its antenna position has also now changed with respect to its surroundings. This could have a knock-on effect as to the best position Rosetta needs to be in to establish a connection with the lander.

Another separate issue under analysis is that one of the two transmission units of the lander appears not to be working properly, in addition to the fact that one of the two receiving units is damaged. Philae is programmed to switch periodically back and forth between these two transmission units, and after tests on the ground reference model, the team has sent a command to the lander to make it work with just one transmitter. As Philae is able to receive and accept commands of this kind in the “blind”, it should execute it as soon as it is supplied with solar energy during the comet’s day.

They have heard from Philae since July 9. Because of comet activity they have had to pull Rosetta back away from the nucleus to protect it, and are now focusing its primary activity on observations, not communications with Philae. They will continue to try to bring Philae back to full functioning life, but the priority is now the comet.

On July 9 Philae successfully transmitted data to Rosetta for the first time in more than two weeks.

Although the connection failed repeatedly after that, it remained completely stable for those 12 minutes. “This sign of life from Philae proves to us that at least one of the lander’s communication units remains operational and receives our commands,” said Koen Geurts, a member of the lander control team at DLR Cologne.

The mood had been mixed over the last few days; Philae had not communicated with the team in the DLR Lander Control Center (LCC) since 24 June 2015. After an initial test command to turn on the power to CONSERT on 5 July 2015, the lander did not respond. Philae’s team began to wonder if the lander had survived on Comet 67P/Churyumov-Gerasimenko.

The intermittent nature of Philae’s attempts at communication are puzzling. Normally, they either would have communications or they would not. For good communications to break off like this repeatedly is puzzling. It is almost as if there is a loose wire causing communications to go on and off, which seems an unlikely explanation for this problem.

This update describes the status of the effort by the Rosetta science team to re-establish a stable communications channel with the Philae lander on the surface of Comet 67P/C-G.

Confirmed contacts between Rosetta and Philae have been made on 13, 14, 19, 20, 21, 23, and 24 June, but were intermittent during those contact periods. For example, the contact on 19 June was stable but split into two short periods of two minutes each. Conversely, the contact on 24 June started at 17:20 UT (on board Rosetta) and ran for 20 minutes, but the quality of the link was very patchy and only about 80 packets of telemetry were received. Prior to this, on Tuesday, 23 June, there was a 20-second contact, but no stable link was established and consequently no telemetry data were received.

There are many reasons why the contacts have been so intermittent, much of it related to Philae’s position on the surface. To improve things, they are carefully adjusting Rosetta’s position relative to the comet while avoiding placing the spacecraft in a position where the coma’s dust will cause problems.

Engineers have begun shifting Rosetta’s trajectory paralleling Comet 67P/C-G in order to maximize communications with the lander Philae.

Commands to adjust the trajectory were successfully uploaded Monday evening; further commands will be uplinked on Thursday evening. The spacecraft will perform two manoeuvres, one on Wednesday morning and the second on Saturday morning. The effect of the two ‘dog-leg’ burns will be to bring the orbiter to a distance of 180 km from the comet and to reproduce the orbiter-comet geometry of the first contact.

We should therefore not expect further news from Philae for the rest of this week.

With a second short contact on Sunday engineers have confirmed that Philae is healthy and capable of doing science. Now they must re-arrange Rosetta’s orbit and re-establish regular communications to get that science started.

After more than six months of silence after its bouncing landing on Comet 67P/C-G, Rosetta’s Philae comet lander has awakened and resumed communications with the science team.

More details here. The data they have so far received, which is still being analyzed, suggests that the lander has awakened previously and gathered data at that time. More to come!

Cool image time! The Rosetta science team has spent much effort trying to locate Philae, which attempted to land on Comet 67P/C-G in November. The image on the right shows what they think is their best candidate, the bright feature in the center. It was not there prior to Philae’s landing attempt.

Because there are many uncertainties, however, this might not be Philae.

Ultimately, a definitive identification of this or any other candidate as being Philae will require higher-resolution imaging, in turn meaning closer flybys. This may not be possible in the near-term, as issues encountered in navigating close to the comet mean that the opportunity to make flybys at significantly less than 20 km from the surface may be on hold until later in the mission. But after the comet’s activity has subsided, Rosetta should be able to safely operate in close proximity to the comet nucleus again.

The other possibility of further refining Philae’s location would come if the lander were to receive enough power to wake-up from its hibernation and resume its scientific study of 67P/C-G. Then, CONSERT could be used to perform additional ranging measurements and significantly reduce the uncertainties on the lander’s location. At the moment, Philae is still in hibernation, but the mission team remain hopeful that, as the comet moves closer to the Sun along its orbit, the lander will receive enough power in the coming weeks or months to wake up and transmit a signal to Rosetta.

Because of the problems Rosetta experienced during its last close fly-by of Comet 67P/C-G the engineering team has worked out a new approach strategy for future observations.

Essentially, they are postponing any close fly-bys for the near future. Instead, they will observe from farther away, while reassessing the situation and planing for later opportunities.

Meanwhile, on April 12 the next opportunity to listen for Philae begins.