Spacecraft Juno to make closest flyby to Jupiterâs largest moon, Ganymede The flyby will be the closest-known since NASA's Galileo spacecraft made its penultimate close approach back on May 20, 2000. Washington: NASA's Juno spacecraft will come within 645 miles (1,038 kilometres) of the surface of Jupiter's largest moon, Ganymede on June 7, the US space agency said on Friday. The solar-powered Juno spacecraft will fly past Ganymede at 1:35 p.m. EDT (10:35 a.m. PDT). The flyby will be the closest-known since NASA's Galileo spacecraft made its penultimate close approach back on May 20, 2000. The flyby will yield striking insights into the moon's composition, ionosphere, magnetosphere, and ice shell. Juno's measurements of the radiation environment near the moon will also benefit future missions to the Jovian system -- encompassing Jupiter, its rings and moons, NASA said.