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Philae landing on the nucleus of Comet 67P C-G
Gerald
post Nov 12 2014, 08:10 PM
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QUOTE (anticitizen2 @ Nov 12 2014, 09:49 PM) *
The flywheel spun around the Z axis in the X-Y plane, so would that make the induced rotation around the Z axis?

In the case, that there is no contact to the ground, and the flywheel is near the center of mass, yes (Philae is almost symmetric to the z-axis). Otherwise the motion (precession / nutation) can be rather complicated.
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fredk
post Nov 12 2014, 08:40 PM
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Here's a very quick and dirty tweak of the higher altitude ROLIS frame:
Attached Image

Based on comparison with this landing site image with stated 500 m radius circle, I find a width of about 38.5 metres for the ground visible in this frame. With a ROLIS fov of 57.7 deg, that gives a distance from the ground of about 35 metres for this image.

Here's a very dirty job regularizing the closer screenshot image to a roughly rectangular shape. Can't be sure about the aspect ratio since it appears some of the image is missing on the bottom:
Attached Image

Comparison with the previous frame gives a width of about 9.1 metres for this image, with corresponding distance of about 8.3 metres from the ground. In other words, still well before landing.

There are big caveats here, of course: the original 500 metre scale was only approximate, the leaked images may only be crops of the full images, and any errors compound as you go from one image to the next.
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machi
post Nov 12 2014, 09:04 PM
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Landing site Agilkia from different imagers and in different scales.
The last one "published" ROLIS image has resolution ~4 cm/pix.
I suppose that full image will be (was) downloaded at 1 Mpix resolution, then full resolution will be ~1 cm/pixel from distance 10 meters.



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PaulM
post Nov 12 2014, 09:15 PM
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The BBC has released a video of Stephan Ulamec's statements in the ESA press briefing:

http://www.bbc.co.uk/news/science-environment-30031531
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MarsInMyLifetime
post Nov 12 2014, 09:17 PM
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I found it curious that those last two ROLIS images depict some apparent rotation which should not have been the case if both were during the same descent. Is it possible that the last image is a post-bounce image that now represents some translation effects of the flywheel? If so, my eyes might be deceiving me but there is perhaps an imprint of a length of leg in the upper right on a "sandbar."


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chemman
post Nov 12 2014, 09:20 PM
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QUOTE (machi @ Nov 12 2014, 02:47 PM) *
Localisation of the published ROLIS image.


Scientists at DPS14 discussing your image smile.gif https://twitter.com/maxmutchler

Attached Image


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OWW
post Nov 12 2014, 09:26 PM
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QUOTE (MarsInMyLifetime @ Nov 12 2014, 10:17 PM) *
I found it curious that those last two ROLIS images depict some apparent rotation which should not have been the case if both were during the same descent. Is it possible that the last image is a post-bounce image that now represents some translation effects of the flywheel? If so, my eyes might be deceiving me but there is perhaps an imprint of a length of leg in the upper right on a "sandbar."

No, apparently philae was spinning once every 9 minutes during the descent. It was mentioned earlier in the stream I think.
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chemman
post Nov 12 2014, 09:33 PM
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QUOTE (MarsInMyLifetime @ Nov 12 2014, 05:17 PM) *
I found it curious that those last two ROLIS images depict some apparent rotation which should not have been the case if both were during the same descent. Is it possible that the last image is a post-bounce image that now represents some translation effects of the flywheel? If so, my eyes might be deceiving me but there is perhaps an imprint of a length of leg in the upper right on a "sandbar."


They did detect a slow rotation during decent, which apparently surprised them. They also think it might have done a little bounce turn when it landed. Also the flywheel was designed to disengage upon touch down. The bar in the upper right is one of the lander legs that's in the camera's field of view.


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MarsInMyLifetime
post Nov 12 2014, 09:48 PM
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QUOTE (chemman @ Nov 12 2014, 03:33 PM) *
They did detect a slow rotation during decent, which apparently surprised them. They also think it might have done a little bounce turn when it landed. Also the flywheel was designed to disengage upon touch down. The bar in the upper right is one of the lander legs that's in the camera's field of view.


I missed the earlier comment about rotation, so thanks for the reminder. I'm aware of the hardware in the corner. The very faint mark I saw is beneath the "shark tooth" shadow on the middle right (upper as in quadrant I but very low in it). I'm not convinced it is real, particularly given the poor resolution and possibility that the photo is still during the original descent. It just happened to match nicely with the meter-length legend below it. I see that conspiracists are seeing alien shadows as well now, so I'm even more removed from my tenuous hypothesis now! Next topic...


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Phil Stooke
post Nov 12 2014, 09:52 PM
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Fantastic work with the landing site location, Machi!

Phil



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... because the Solar System ain't gonna map itself.
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SpaceScout
post Nov 12 2014, 10:03 PM
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...still no images from the surface..


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Gladstoner
post Nov 12 2014, 10:14 PM
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QUOTE (SpaceScout @ Nov 12 2014, 04:03 PM) *
...still no images from the surface..


Images could be delayed if there is something of scientific interest.
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djellison
post Nov 12 2014, 10:18 PM
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I would be surprised if we see anything more before the press conf tomorrow afternoon CET.

FWIW - reading very much between the lines ( the notion that after the first touchdown there was an approx 2hr period of the spacecraft exhibited rotation and then came to a stop which infers a long bounce ) - my basic math suggests a 2hr bounce would reach about 530m altitude and start with a 0.3m/sec rebound.
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Explorer1
post Nov 12 2014, 10:23 PM
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And with the speed of the nucleus's rotation, the surface was moving underneath a great distance too! Hopefully they can track down where it ended up.
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djellison
post Nov 12 2014, 10:30 PM
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2 hrs would put us 1/6th of a comet rotation apart and therefore the second touchdown might be off the 'head' and closer to the back of the neck of the comet. Or it might have got a direction to the rebound sending it another direction completely. I'm not very confident that a 500m 2hr bounce really did occur - but it's a thrilling thought. 2 landings for the price of one smile.gif

Fingers crossed OSIRIS can spot Philae on the surface and we can then compare that to Machi's exceptional location chart.
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