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Headshot of Emily Lakdawalla

Philae status, a day later

Posted by Emily Lakdawalla

13-11-2014 13:26 CST

Topics: Rosetta and Philae, pretty pictures, pics of spacecraft in space, comets, mission status, comet Churyumov-Gerasimenko, spacecraft

The Philae team scrambled all morning to comprehend the initially confusing status of the lander, and the picture is much clearer today. But I can't talk about clear pictures without showing you the best thing from this afternoon's press briefing, an animated gif of the descending Philae, captured by the OSIRIS camera:

Philae falling


Philae falling
This animation shows the Philae lander falling away from Rosetta from 10:24 to 14:24 on November 12, 2014, in images taken an hour apart, beginning about two hours after the spacecraft separated at 08:35.

I now appreciate why there was so much confusion yesterday. When Philae initially touched down, that triggered the end of its descent sequence and the start of its first block of science activity. Its instruments dutifully performed their measurements and Philae relayed these back to the orbiter -- all while Philae was steadily climbing away from the comet at a speed of 38 centimeters per second. At the same time, the internal flywheel was slowly being braked, and that caused Philae to rotate, which was incredibly confusing to a team that thought the spacecraft was stationary on the comet surface.

Here are a few bullet points from the press briefing:

  • They do not yet know exactly where Philae landed (more on that below).
  • After the initial impact, they rebounded at about 38 centimeters per second -- about a third of their 1-meter-per-second impact velocity.
  • They saw rotation for about 2 hours after impact, and then rotation stopped (this was while the spacecraft was on its long first bounce).
  • They lost the link about 30 minutes after its final touchdown.
  • The solar panels are only getting illuminated for 1.5 hours of each 12-hour comet day, which is much, much less than they need in order to keep the lander going after its batteries run out.
  • Contrary to earlier reports, the solar panels are not damaged.

Here are few more bullet points on spacecraft activity and status from an ESA update:

  • Rosetta is operating nominally; the network systems and overall ground segment to control the mission are nominal
  • Last night, Rosetta lost contact with Philae as expected when it orbited below the horizon just after 20:00 CET.
  • Contact was re-established this morning at 06:01 UTC / 07:01 CET, and the Philae-Rosetta radio link was initially unstable.
  • As Rosetta rose higher above the Philae landing site, the link became very stable and the lander could transmit telemetry (status and housekeeping information) and science data from the surface.
  • This morning's surface link was again lost due to Rosetta's orbit at about 09:58 UTC / 10:58 CET. Ignacio explains that with the current orbit, Rosetta will have, typically, two Philae communication windows per day.
  • The next window opens at 19:27 UTC on the spacecraft and runs through to 23:47 UTC spacecraft time.

Where is the lander on the comet? They don't know yet. They think they know approximately where it is, thanks to data from the CONSERT instrument. But at least one member of the science team disagrees with this assessment; Holger Sierks thinks it's about the same distance away from the initial landing site, but in a 10:00 direction rather than a 3:00 direction.

Where did Philae land?


Where did Philae land?
Where did Philae land? Its initial impact point is precisely located within the red square. Its final landing location is not yet known, but CONSERT radar sounder data suggests it is somewhere within the blue diamond.

I was initially surprised by this location because it is located prograde (in a rotational sense) from the touchdown site, but after a little further thought I think it makes sense. Here's the important detail: When Philae was descending, it was in an elliptical orbit around the center of gravity of the comet. That orbit intersected the ground at the intended landing site in such a way that the horizontal component of Philae's motion was parallel to the orbital motion of the surface at that point, which is another way of saying that the spacecraft landed vertically. (Mission manager Stephan Ulamec described this geometry in a press briefing earlier this week.) So when it bounced off, it bounced off close to vertically in the reference frame of the comet's surface, and then when it landed it landed a relatively short horizontal distance away from the initial impact site. (By this logic, either the blue diamond location from CONSERT or Sierks' location makes equal sense.)

They had representatives from all the camera teams -- Jean-Pierre Bibring for CIVA, Holger Sierks for OSIRIS, and Stefano Mottola for ROLIS. Mottola showed a ROLIS image captured just 40 meters above the very first impact point. Mottola said the gravels at the initial impact site ranged in size from millimeters to meters in diameter. He pointed at a small boulder in the upper right of the image and mentioned the dust that appeared at its base; he said it is not clear whether the dust is accumulating at the base, or if the rock is being exposed by sublimation.

ROLIS view of Churyumov-Gerasimenko from 40 meters altitude

ESA / Rosetta / Philae / ROLIS / DLR

ROLIS view of Churyumov-Gerasimenko from 40 meters altitude
The large block at upper right is about 5 meters across; the Philae landing gear intrudes into the upper right corner.

The star of the morning was ÇIVA. Bibring showed 6 ÇIVA images forming a 360-degree panorama around the lander.

ÇIVA's view around Philae

ESA / Rosetta / Philae / CIVA

ÇIVA's view around Philae
Philae has returned the first panoramic image from the surface of a comet. The view, captured by the CIVA-P imaging system, shows a 360° view around the point of final touchdown. Parts of Philae’s landing gear can be seen in some of the frames.

It's a little hard to understand what's going on in this photo, so I've stretched the contrast a bit and annotated it, and rotated it so that the horizon is level:

ÇIVA's view around Philae (annotated)

ESA / Rosetta / Philae / ÇIVA / annotated by Emily Lakdawalla

ÇIVA's view around Philae (annotated)

So the lander is clearly tilted, with one image showing only sky. The lander has three legs, one in "front" and two to the side rear. The rear right leg is "down" in the image, while the front and rear left legs are up. Taken together with the geometry of the horizon -- which curves more than 180 degrees around the lander -- and it appears that the lander may actually be in a hole. When I imagined this, I laughed, imagining a comet jet suddenly popping Philae out of the hole like a pea from a straw. Or maybe an exogorth is down there somewhere! But, to get more serious, being in a hole would explain why the solar panels are getting so small an amount of illumination, and may unfortunately doom the lander to the short life dictated by its battery power.

What happens from here? They're doing as much science as they can without making any mechanical motions. That means no MUPUS surface properties experiments, or use of the APXS, and no deliveries to the gas chromatograph mass spectrometers. There is discussion of possibly using some of these moving devices to attempt to pop the lander up off the comet again, to try to get it into a position where they could recharge the battery. But if they do that, it will be a last-ditch effort.

I have more to report but no more time to report it today. I'll be at ESOC for one more day, tomorrow, and I'll try to bring you another update then.

See other posts from November 2014


Or read more blog entries about: Rosetta and Philae, pretty pictures, pics of spacecraft in space, comets, mission status, comet Churyumov-Gerasimenko, spacecraft


CosmosQuest: 11/13/2014 03:37 CST

Thanks for another excellent recap Emily. One thing that has confused me why do they keep flip flopping on whether or not the harpoons fired? this is especially disturbing in light of the fact that they are discussing as a last ditch effort possibly engaging the harpoons again to try to move the Landers position. should not they first determine for sure if the first time possibly added to the rebounding of the craft on initial landing?

Adolf Schaller: 11/13/2014 03:49 CST

Is that y direction (i.e., in the 3 o'clock direction) in the graphic (corresponding to the orientation of the first Rolis image) the prograde direction? If so, it would make sense and the weird right-angle ricochet I was trying to understand vanishes. I had assumed the first Rolis image was oriented so that it was rotating towards the top (the z or noon) direction, which was the source of my confusion. I am of the same opinion of what Buzz Aldrin had pointed out in a tweet I saw somewhere yesterday: the planned choreography to exploit the rotation of the comet to minimize lateral or fore-aft motion with respect to the surface was indeed a nifty way to cancel such motion and ensure a near-vertical drop onto the surface. Its a shame that none of the devices the lander was equipped with to secure it on the surface at that initial touchdown point failed. One can't help fantasize on the distribution of outcomes of a thousand trial Philae landers sent on their way under identical circumstances...we are forced deal with the one outcome that was dealt. 8/ Oh well...we are reminded we live in an accidental universe.

Rakesh: 11/13/2014 03:58 CST

I wished Esa a hearty congratulations yesterday due to the landing news but looks like the landing isn't all that great after all. Thrusters did not fire, harpoons did not fire, and one leg is not on the ground. The craft bounced 3 times. Now they say the battery life is an issue and Philae may die but overall the Philae story is a "success". How so if Philae won't be been able to perform all the experiments ? I wager that the scientists got caught in the hoopla (and politics) of "history making" and spoke too soon without delving into the landing data coming out.

Adolf Schaller: 11/13/2014 04:42 CST

Such total disappointment is not justified. A complex craft equipped with a suite of complex science experiments and cameras HAS, as a matter of absolute, incontrovertible FACT, been delivered alive onto the surface of a comet adorned with undreamed complex topography, and IS as a matter of FACT transmitting data from most if not all of the experiments that are operating (if not necessarily under optimum conditions). Its not 'hoopla', or 'politics' to characterize this as a historic achievement. Philae and the Rosetta team has as a matter of demonstrable fact succeeded in delivering our senses intact to the surface of a comet.

lodaya: 11/13/2014 10:46 CST

Emily, thanks for the annotations. The question seems to be: when Philae bounced, did it move faster at relative velocity +p or did the comet rotate faster under it at a relative velocity -c? But then the travel distance could be anything between the two extremes. My guess is they have to search the Osiris images of the comet head, looking for cliffs and pits. Some of the recovered data might give clues. A question: at what point in the battery balance situation is it worthwhile to take the chance and drill? Either you stay where you are and get some data, or you fall further into the pit, which gives you access to more of the interior which you try to get data out of before the batteries go, or by the reaction (which one can try to anticipate) you might be bounced out of the pit and hope to live another day.

andrevh: 11/14/2014 05:00 CST

The problems with the harpoon were already known in 2013: The makers claimed to have found a solution to the problem of nitrocellulose not working in a vacuum. During the landing it did not work, so maybe the changes that a second attempt at firing them will also not work.

thebigh: 11/14/2014 05:50 CST

I have a quetion regarding the solar power. Why does less solar power endanger the mission? Can't Philae just remain dormant for longer while its battery charges, then do science when it has enough energy? Or is it necessary that Philae be powered on continually?

R. Scott Russell: 11/14/2014 09:22 CST

thebigh: I think at minimum they would need the batteries and solar panels to maintain some type of thermal control, maintaining just the right temperature for some of the equipment and delicate electronics and optics. Without this the equipment might quickly degrade.

nealmcb: 11/14/2014 10:05 CST

Wonderful reporting - thank you! I want to visualize all this on the 3D models that they provided (.obj and .wrl format) . Can we get any data on where rosetta was when taking its pictures of the landing site? Any precise data on rosetta's current orbit, to correlate with the times they're giving for link availability?

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