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PASADENA — NASA’s Deep Space 1 spacecraft will swoop within 1,240 miles of a comet on Saturday in an attempt to image for only the second time ever the dark nucleus of one of the frozen balls of dust and ice. 

The robotic probe will make its closest approach to the comet Borrelly at 3:30 p.m. PDT Saturday. If the flyby is successful — and the odds are slim — the battered probe’s camera will snap up to 32 black-and-white images of the comet’s heart. 

Confirmation of whether the attempt succeeded will take 12 minutes to reach Earth. Mission members hope to receive the first image of the comet’s nucleus within three hours of the encounter. 

The probe will also attempt to learn more about Borrelly’s surface, measure and identify the gases it gives off and study the interaction of the solar wind with the comet. That process creates the comet’s distinctive tail. 

The risky flyby may be the swan song for Deep Space 1, which wrapped up its main mission to test a dozen new technologies two years ago. 

Engineers at the National Aeronautics and Space Administration’s Jet Propulsion Laboratory fear that dust and debris kicked off by the comet will knock the probe off kilter and possibly destroy it. Even if the probe survives the battering by minute particles traveling at 36,900 mph, its $164 million mission will end in November as its supply of fuel dwindles to nothing. 

At the time of flyby, the comet and spacecraft will be approximately 137 million miles from Earth.