Giotto’s brief encounter, Twenty years ago Options

[Rakhir]

Giotto’s brief encounter
http://www.esa.int/esaCP/SEMSZ0NVGJE_index_0.html

Twenty years ago, in the night between 13 and 14 March 1986, ESA’s Giotto spacecraft encountered Comet Halley.

[ollopa]

A wonderful reconstruction, but in the interests of absolute historical accuracy I must remind people that these were not the images we saw on the night. I anchored a two-hour TV programme during the encounter and no-one warned us that Giotto was not Voyager. The first and only picture on the night - during hours of live TV coverage across Europe - was this one.

The implications for European space policy were profound. Margaret Thatcher was Prime Minister in the UK and was watching the BBC coverage in the private apartment at Downing Street with, I think, Sir John Fairclough, her science advisor. She asked: "What are we paying for this?". And I'm afraid the rest is history.

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[ynyralmaen]

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.