Gravity lends a hand
Stories from Physics for 11-14 14-16
Gravity assists are used to alter the path and speed of spacecraft. Perhaps the most extended gravity assist ever achieved was proposed by the Italian mathematician Gaetano Crocco and applied in the Voyager mission. In a ‘rare moment of great elation’, Crocco noted that a spacecraft launched in 1977 would encounter an alignment of the planets highly favourable to providing multiple gravity assists that hadn’t occurred since 1801 and wouldn’t reoccur for 176 years. The spacecraft would first encounter Jupiter, two years after launch, where it would be accelerated by 11 km/s and deflected though 97° towards Saturn, which it would reach the following year, then encounter Neptune and Pluto. He labelled this route the ‘grand tour’.