Long-dormant Cassini Instrument Back Online

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NASA engineers have revived a science instrument aboard the Cassini spacecraft in orbit around Saturn, bringing the 15-year-old probe back to full strength for the first time in nine months.

On March 16, engineers reactivated Cassini’s plasma spectrometer, one of 12 instruments used by the spacecraft to study Saturn and its many moons. It is designed to measure the energy and electrical charge of particles around Saturn.

The spectrometer suffered an apparent short circuit last year and was switched off in June to avoid further damage while mission managers studied the glitch.

“The investigation led to the conclusion that tin plating on electronics components had grown ‘whiskers,’” NASA officials explained in a mission update March 19. “The whiskers were very small, less than the diameter of a human hair, but they were big enough to contact another conducting surface and carry electrical current.”

Scientists still do not fully understand why the so-called metal whiskers develop on tin and other metal materials on spacecraft, as well as on machines on Earth. But the whiskers inside the Cassini electronics should not pose a problem.

“It is believed that these or additional tin whiskers that may grow on Cassini cannot carry enough current to cause problems, but will burn out on their own like a lightweight fuse,” explained NASA officials with the Jet Propulsion Laboratory in Pasadena, Calif., which oversees the Cassini mission.

Cassini’s odd metal whisker problem began May 1, when engineers first detected surprising voltage changes in the spacecraft’s equipment. The voltage readings hinted that a short circuit was in process. When the glitch occurred again June 11, mission managers opted to shut down the plasma spectrometer until it could be explained.