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OU Lecture 2007: Brave Giotto

Updated Tuesday, 26th June 2007

Giotto was approching Halley's Comet. Would the DIDSY team come good?

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Our predictions had said that we would detect our first dust impact between minus ninety and minus eighty-five minutes. The clock kept on ticking. The minutes passed. Nothing. We were the only one not working. So there we are: the DIDSY team – we were the Dust Impact Detection System – sitting there at our monitors, very, very quiet. We were watching a row of zeros literally passing through our screen. Was DIDSY going to become DUDSY? Had our instrument packed up? Important scientific thoughts were going through my brain – such as, “where could we hide?” “Who was responsible?” “Who could I blame” Then, thank the lucky stars, the sweetest “1” I had ever seen. It happened at minus seventy-two minutes. We had the first dust impact. It was wonderful. Fingers uncrossed, cheers went up. We were happy too. My goodness were we happy!

But we were still more than a hundred and fifty thousand kilometres away from the target but closing fast. We converted the data into a sound file so you could hear it as if you had been sitting on the front shield of the spacecraft. This is how it would have sounded when we were far out – just the occasional hit on the shield. We moved in. The hits started to build up. Twenty minutes to go and the spacecraft is beginning to take quite a battering. In fact, we now start to get the occasional impact on the rear shield, so bigger particles are beginning to bombard Giotto. Will the shields hold, Scotty? We are now minutes away from the closest approach. Whatever happens, it doesn't matter. It's a success. We have got lots of data. But how close could we get? Moments later and some of the data channels started to saturate, we are getting so many hits. We are within one minute from closest approach. And then – it happened. We lost everything. Screens go blank. We assumed a big particle – the spacecraft had been lost. But it exceeded our wildest dreams. Cheers, hugs, the champagne started to flow. The end.

Well was it? No. We hadn’t finished the first glass of champagne before a voice piped up from the other side of the control room. We have still got some data. What’s going on? But there is something strange about it. It wasn't like before. It was coming through in bursts. We were getting a burst of data then a blank, then a burst of data again. What we think happened was that a particle had hit, probably on the very edge of the shield, and it had set the spacecraft nutating – or wobbling. Now the radio transmission back to the earth was in a narrow beam so, with the spacecraft wobbling, this meant that the beam was waving around. So it was literally going backwards and forwards across the Earth and we were just picking up bursts of data. But there was actually an on-board system to damp out the wobbling and, over the next twenty minutes the wobbling gradually died down. And so we had the situation about twenty minutes later that we were actually receding from Halley’s Comet still taking data, which we never imagined could happen. But actually, Giotto was not quite as before. The camera was blind. It wasn't sending any pictures. The temperatures were all over the place and actually fifty per cent of the instruments were dead. But DIDSY was alive, or at least ninety per cent of it was alive. Well, what do you do with a half-working comet-probe? Well, you send it to another comet of course.

But hang on. One small problem. We had virtually no fuel left. Well there is a way around that because in space there is something, we do have something, that is very close to a free lunch and it's called the gravity assist manoeuvre. If you send your spacecraft to fly past a planet or a large body, and if you get everything just right, the geometry,the speed and so on, you can actually use that planet to sling you off in another direction. You can change the course for free. And the clever people who were controlling the Giotto spacecraft realised that the orbit, it was actually an orbit that would bring it back to Earth, about four years later. So in 1990, Giotto flew over the rooftops. About a thousand kilometres. And it was shot off towards another comet – Grigg-Skjellerup – a comet that you will never have heard of – totally anonymous. But that is what we wanted. We wanted to compare it with Halley.

Well, what happened? We got there. At Halley we got about fifteen thousand impacts that we measured. At Grigg-Skjellerup we got three. A lot less active a comet and we were also travelling more slowly, relatively speaking, which meant we had less sensitivity. Anyway, it was wonderful. We got more scientific papers. European taxpayers got wonderful value for money. Giotto survived that too. We built it well. But what to do with it next? Well I actually formally suggested to ESA, because I worked out that we could actually crash it into the moon, not for a bit of fun – well it would have been fun to be honest – but I think we could have got some good science out of it. But that was a step too far for ESA. So it was sadly turned off. And where is it now? Well, it's trolling around the solar system, forgotten by almost everybody but certainly not forgotten by those who worked on it over twenty years ago. Actually I think this mission was very, very important for the European Space Programme. It really put Europe on the map in terms of the world exploration, space exploration scene. And from then on I think Europe and ESA was taken very seriously.


With thanks to:

  • ESA

The Open University Lecture 2007

This is part six of ten

Next: Beagle 2





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