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Like an ancient mariner, NASA’s Galileo spacecraft navigates by using the
brightest fixed stars as reference points. So when the craft misbehaved briefly
en route to Europa last June, engineers wondered if its star tracker was playing
up. After a week’s investigation, they decided that it was the reference star
that was to blame. The star, Delta Velorum, turns out to be two stars orbiting
each other. During an eclipse of one star by the other, its brightness dipped
and the star tracker didn’t recognise it, says Paul Fieseler, an engineer at
NASA’s Jet Propulsion Laboratory in Pasadena.