The Reg chats with Voyager Imaging Team member Dr Garry E Hunt

Nearly nixed by Nixon

The team spent the next five years finalising the spacecraft and the trajectories. Voyager 2 would be launched first, followed by Voyager 1 a few days later in 1977. An opportunity to visit Pluto was scrapped in favour of a higher-priority target in the form of Saturn's moon Titan. The team decided that Voyager 1 would take a close look at Io and Titan, which would mean it would be on a trajectory that would leave it unable to visit Uranus or Neptune. That would be left to Voyager 2, which could still have its course altered to take a look at Saturnian moon Titan in the event its sister spacecraft failed.

Not that going beyond Saturn was officially on the cards. The mission, renamed Voyager in 1977, was only funded as far as the ringed gas giant when it was approved in 1972. "Nixon was the president. He wouldn't agree to a funding for more than Saturn, because that would obviously take it into another presidential period, and he couldn't be sure of being in office, which he wasn't.

"We had already realised that you could do Jupiter-Saturn-Uranus-Neptune, and we knew that if you filled up to brimming point the spacecraft with all the fuel it ever needed, it'd be OK. We did. But we never told anybody."

Naughty.

Back to school

"You've actually got a 10-day window. That is how close [it was]. A 10-day window in 175 years. That is pretty, pretty tight," Hunt recalled from the run-up to launch. The only Brit on the Voyager project accepted a position at University College London (UCL) and began building a small team to process the images that would be sent back by the probes.

The Interactive Planetary Image Processing System (IPIPS) lab at UCL is something of which Hunt is clearly proud. "We built the most phenomenal team. We wrote every piece of software. We had hardware specially set up to do it." The heart of the hardware in question was a VAX 11/780, with the computer equipment used by the team costing an eye-watering £350,000, nearly £1.5m in today's money.

As for credit for the UK's contribution to the stunning images returned by the Voyagers, Hunt reckoned it was "reasonable". The fact that the cloud-tracking software would later find its way into weather forecasting on Earth and commercial TV contracts, beating out systems from the Met Office, was undoubtedly satisfying.

Launch

With his imaging team in place, and ready to accept reams of magnetic tape delivered direct from JPL to UCL via Boeing 747, and the Pioneer flyby showing that the Voyagers should survive at least past Jupiter, Hunt travelled to Cape Canaveral to watch the Titan IIIE launches of the probes.

Sat behind the press corps, the scientists watched the countdown clock approach zero. Hunt recalled how it felt, waiting for the precious cargo to lift off, knowing there would not be another chance for several lifetimes. "We're sitting there on the countdown, and then the moment has come, and then you're watching it and you think, well, you just think about it. I had put five years of my life on the block to do that. If it had failed, then that was the end of my career."

JPL, we've had a problem

Things began to go wrong for the spacecraft pretty much immediately. After a successful launch, a jubilant Hunt was brought back down to earth by an engineer.

"It had an instant problem... because it goes all folded up, and then it springs up. Well, it didn't spring up. It was still sort of flopping around a little bit, a bit like a garage door.

"What they actually did was to get the thing to spin very fast, and the angular momentum was enough to click it up. And then for Voyager 1, which hadn't been launched, they actually put, effectively, a better garage door opener in."

The spacecraft would suffer more problems on their way to the gas giants. Voyager 2 encountered issues with its radio receiver while Voyager 1's scan platform (upon which the instruments were mounted) jammed briefly after taking humanity's first view of the crescents of both the Earth and the Moon in the same frame.

Two years to Jupiter

For Hunt and his team, the pace of work did not let up. With less than two years until Voyager 1 would encounter Jupiter, there was stuff to do. "The gap between '77 and '79 was to get everything in order, because we were not in order. We hadn't got all the data analysis techniques organised, and we had to get all that dealt with in that period.

"We had to get everything checked and to make sure it worked smoothly so that when we received data it could be properly analysed, so we could produce colour pictures, we could produce proper analyses, so all the cloud-tracking techniques and the surface analyses that Larry [Soderblom] wanted to do had to be dealt with. So all these things had to be properly developed and refined, and all the major objectives that each working group wanted were crystallised and prepared for, because there was quite a battleground between what various people wanted to do."

The code aboard the spacecraft was constantly modified as ground-based discoveries (for example, sodium around Io) required the mission to be tweaked to take in new targets as science objectives changed. Even new information gleaned between Voyager 1 and 2 could result in an adjustment of the scheduling in order to take a more detailed observation of something spotted by Voyager 1 with Voyager 2. Hunt found himself effectively commuting to Los Angeles for JPL meetings while still teaching classes at UCL.

Famously, Voyager transformed our understanding of the outer planets. For Hunt, Io remains a highlight of the mission. He recalled one of the researchers struggling with an image taken of the Jovian moon and telling the imaging team: "There's something wrong with this picture. It's got a bump. I can't quite make it fit." The bump turned out to be the first evidence of a volcano on another planet.

The discoveries at Jupiter came thick and fast. The team found new satellites and discovered a thin ring surrounding the planet. Lightning was discovered in the atmosphere, and data on the structure of the atmosphere, its winds and clouds, began to be built up. Hunt observed wryly: "It was all fascinating. The new discoveries. The new satellites. We were always running out of names for these wretched things!"