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Giotto’s brief encounter, Twenty years ago
ngunn
post Nov 16 2009, 11:11 PM
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QUOTE (elakdawalla @ Nov 15 2009, 03:32 AM) *
Must remember to post it tomorrow or Monday!


I'm still waiting. wink.gif

I notice you already have a great Vega 1 animation posted which shows the nucleus looking bright against the background, unlike the Giotto images. I'd be interested to know the geometrical relationship beween the two, the lighting directions etc. Now I've probably complicated the task and will have to wait even longer for your post!
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ynyralmaen
post Nov 17 2009, 09:48 AM
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I very definitely remember staying up late to watch the BBC coverage, and fortunately I still have a copy of the programme (can't find it posted anywhere on the web though). The BBC did show the live stream of gaudy images as released live by ESA; you can briefly see samples of these at 02:37 on this video:
http://www.youtube.com/watch?v=d9m3lPFUeeA&NR=1

... and the way they disappeared from our screens shortly before closest approach, at 02:57 on this one:
http://www.youtube.com/watch?v=oiRghs0SiR4...feature=related

In the book, "Giotto to the Comets", Nigel Calder states that the blame for the release of the false-colour image stream rather than more easily-decipherable ones rests with a TV producer working with ESA who regarded the greyscale images that the camera team had recommended streaming as being too boring. According to the write-up on the encounter in Astronomy magazine (I guess that would be something like the July 1986 issue), apparently Keller did provide a running commentary and instant, apparently pretty accurate interpretation of the greyscale images to the press as the images came in. The TV and radio correspondents were concentrating on their live coverage however, so it was the reporters from the print media who knew best what was going on! The BBC coverage itself was a bit disjointed because it was a joint Sky at Night and Horizon production: Patrick Moore was in Darmstadt with much better access to information on the encounter's progress, but I recall that most of the coverage came from Greenwich, where James Burke was consulting several high profile experts. The only information on which they could base their comments was however the stream of false-colour images alone, and they understandably had a very hard time explaining what they were looking at. On top of the colour scale, added confusion resulted from the fact that the nucleus itself was dark, not bright. The camera software was written to track the brightest part of the scene, so latched on to the two bright jets at one end of the nucleus as the nucleus filled the field of view.

We must bear in mind that capturing these images was particularly challenging because the camera was mounted on the side of a rapidly-spinning spacecraft (spinning was great for the plasma instruments). The images had to be timed to be captured just as the nucleus swept across the camera's field of view during each spin. The camera itself was pointing "outwards", perpendicular to the spin axis, and actually viewed the nucleus through a rotatable flat mirror. The camera mirror and its baffle had to be rotated to keep in step with the nucleus's motion across the sky as viewed from Giotto, under software control based on tracking the brightest point in the image. It appears that the mirror became pitted due to dust impacts, so the quality decreased towards the end, and the large impact just before closest approach caused the spacecraft to lose balance and to start nutating; sporadic signal losses then occurred. The baffle itself was largely destroyed then or shortly afterwards. Communications were restored thanks to dampers in the spacecraft that brought the nutation back to a tolerable range during the outbound phase.

It was the then-16-year-old Lee Sproats, sitting on the panel in Greenwich, who first guessed correctly that something had gone seriously wrong when the images disappeared, and largely because of that he got to appear on the TV programme for Giotto's second encounter in July 1992.
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Stefan
post Nov 17 2009, 01:31 PM
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QUOTE (machi @ Nov 14 2009, 09:50 PM) *
I have a question. Can I put here some improved Halley comet images, or do I have to write to dr. H. U. Keller first? There in an information on PDS data set, that the data are copyrighted and the owner of copyright is dr. H. U. Keller. Data are free of charge for scientific purposes. But if I post them here, are they scientific purposes?

A message from Dr. H.U. Keller:

Hallo machi (and others),

I am really impressed (and not for the first time) what members of the general space community can do with images. The GIF animation impressively shows how small the actual transmitted images (near closest approach) are, only 74 by 74 pixels, and it shows how complex the corrections are for the geometric distortion of the images taken from a rotating spacecraft with a line scanning camera. It also shows that the tracking (autonomous by the computers of the camera) worked very well until Giotto was hit by debris. Here is a movie (6MB) for your viewing pleasure simulating the approach, but made from a composite image where 64 images are inserted in an earlier (large image) image providing more and more resolution around the brightest feature. © 1986-2009 MPS.

Finally a word concerning the copyright. The copyright was introduced to control (or prohibit) manipulated images. Publication in a non-profit environment is free and encouraged. So please help to maintain the integrity of the images and the scientific results.

Thanks for your interest. Regards,
H. Uwe Keller
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ngunn
post Nov 26 2009, 07:49 PM
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Emily has just posted the Giotto Halley movie to her blog, which last September also featured the Vega 1 movie. Here are the two links brought together for convenience:
http://www.planetary.org/blog/article/00001641/
http://www.planetary.org/blog/article/00002230/
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machi
post Jan 13 2010, 11:20 AM
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QUOTE (Stefan @ Nov 17 2009, 02:31 PM) *
A message from Dr. H.U. Keller:

Hallo machi (and others),

I am really impressed (and not for the first time) what members of the general space community can do with images. The GIF animation impressively shows how small the actual transmitted images (near closest approach) are, only 74 by 74 pixels, and it shows how complex the corrections are for the geometric distortion of the images taken from a rotating spacecraft with a line scanning camera. It also shows that the tracking (autonomous by the computers of the camera) worked very well until Giotto was hit by debris. Here is a movie (6MB) for your viewing pleasure simulating the approach, but made from a composite image where 64 images are inserted in an earlier (large image) image providing more and more resolution around the brightest feature. © 1986-2009 MPS.

Finally a word concerning the copyright. The copyright was introduced to control (or prohibit) manipulated images. Publication in a non-profit environment is free and encouraged. So please help to maintain the integrity of the images and the scientific results.

Thanks for your interest. Regards,
H. Uwe Keller


Thanks for message. Even if images from Giotto aren't so perfect like from Deep Impact, I still think, that this images and whole mission was great achievement. Flyby speed over 60 km/s, low datarate, dangerous environment (evidently more dust than in other cometary flybys, in fact most active comet with imagery) and no one knew like cometary body looks (not easy task for automatic targeting).

I send my second mosaic of comet Halley (first isn't available on net).
All images resampled to 50 m/pix. False color from lower resolution images.



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ElkGroveDan
post Jan 13 2010, 02:51 PM
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Amazing work Machi. It's like an entirely new mission to give us a better look at Halley.


--------------------
If Occam had heard my theory, things would be very different now.
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machi
post Jan 15 2010, 12:51 PM
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Thanks Dan!

Third Halley's comet mosaic (and I think my last dayside fullres mosaic for long time). It's full version resampled at 25 m/pix.
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