THE GRAND TOUR

The idea behind the Voyager project originated in 1964, when NASA scientists noticed that an unusual planetary alignment would occur in the late 1970s, allowing a single spacecraft trajectory to pass close to Jupiter, Saturn, Uranus and Neptune in turn. The gravitational boost acquired at each encounter would send the probe on its way to the next planet. Initially dubbed the ‘Grand Tour’, the mission went through various design changes as NASA struggled to match scientific aspirations to the available budget. In the end, two virtually identical spacecraft were launched: Voyager 2 on 20 August 1977, and Voyager 1 – on a faster trajectory which saw it reach Jupiter first – 16 days later.

Although the Grand Tour could have been completed with a single spacecraft, there were advantages in using two. First, it meant one of them could take greater risks. For example, Voyager 1 got twice as close to Jupiter, with its hazardous radiation field, than Voyager 2, which erred on the side of caution. When Voyager 1 reached Saturn, NASA also wanted to explore its intriguing moon Titan, but this diversion prevented Voyager 1 from reaching Uranus and

Neptune – a task that was left for Voyager 2.