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Earlier in January, a defective spring aboard the FASTSAT mothership had prevented the NanoSail-D from separating from it. For reasons still unknown, however, it spontaneously launched itself free on January 17th. On January 20th, the spacecraft unfurled its solar sail, only the second such to be deployed in space after Japan's IKAROS probe last year, and the mission is now proceeding as scientists had hoped.
NASA has often caught a lot of bad luck in the past on too many missions, so its nice to see them catch some good luck for a change, especially in testing a technology that could be very vital to a number of future space efforts.
(Plus for those who didn't spend (mis-spend?) many hours of their youth playing tabletop RPGs, a 'saving throw' refers to a D&D trope where a character has to avoid a bad outcome by a literal roll of the dice.)