Philae landing on the nucleus of Comet 67P C-G |
Philae landing on the nucleus of Comet 67P C-G |
Nov 12 2014, 08:10 PM
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#256
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
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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Nov 12 2014, 08:40 PM
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#257
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Senior Member Group: Members Posts: 4246 Joined: 17-January 05 Member No.: 152 |
Here's a very quick and dirty tweak of the higher altitude ROLIS frame:
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: 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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Nov 12 2014, 09:04 PM
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#258
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Member Group: Members Posts: 796 Joined: 27-February 08 From: Heart of Europe Member No.: 4057 |
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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Nov 12 2014, 09:15 PM
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#259
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Member Group: Members Posts: 206 Joined: 15-August 07 From: Shrewsbury, Shropshire Member No.: 3233 |
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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Nov 12 2014, 09:17 PM
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#260
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Member Group: Members Posts: 148 Joined: 9-August 11 From: Mason, TX Member No.: 6108 |
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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Don |
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Nov 12 2014, 09:20 PM
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#261
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Junior Member Group: Members Posts: 33 Joined: 15-April 09 From: Wilmington, NC U.S.A. Member No.: 4738 |
Localisation of the published ROLIS image. Scientists at DPS14 discussing your image https://twitter.com/maxmutchler -------------------- -------------
-Ned |
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Nov 12 2014, 09:26 PM
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#262
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Member Group: Members Posts: 710 Joined: 28-September 04 Member No.: 99 |
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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Nov 12 2014, 09:33 PM
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#263
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Junior Member Group: Members Posts: 33 Joined: 15-April 09 From: Wilmington, NC U.S.A. Member No.: 4738 |
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. -------------------- -------------
-Ned |
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Nov 12 2014, 09:48 PM
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#264
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Member Group: Members Posts: 148 Joined: 9-August 11 From: Mason, TX Member No.: 6108 |
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... -------------------- --
Don |
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Nov 12 2014, 09:52 PM
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#265
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Solar System Cartographer Group: Members Posts: 10153 Joined: 5-April 05 From: Canada Member No.: 227 |
Fantastic work with the landing site location, Machi!
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Nov 12 2014, 10:03 PM
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#266
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Junior Member Group: Members Posts: 31 Joined: 3-August 14 From: Germany Member No.: 7229 |
...still no images from the surface..
-------------------- space scout
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Nov 12 2014, 10:14 PM
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#267
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Member Group: Members Posts: 714 Joined: 3-January 08 Member No.: 3995 |
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Nov 12 2014, 10:18 PM
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#268
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
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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Nov 12 2014, 10:23 PM
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#269
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Senior Member Group: Members Posts: 2082 Joined: 13-February 10 From: Ontario Member No.: 5221 |
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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Nov 12 2014, 10:30 PM
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#270
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
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
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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