Cassini has fallen back on a reserve set of propulsion thrusters during its extended tour of Saturn.
Lacking space tugs or robotic repairmen, the Cassini spacecraft activated its backup thrusters because of slow degradation in the performance of its main thrusters. The primary thrusters have kept the space probe going since its launch in 1997 until now.
The Cassini mission has uncovered many new findings about Saturn, its rings and local moons. It sent its Huygens probe down to peer beneath the orange shroud of methane around the moon Titan, sampled icy particles spewing from cold Enceladus and surveyed bizarre weather patterns on Saturn.
The thrusters are used for making small corrections to the spacecraft?s course, for some attitude control functions, and for making angular momentum adjustments in the reaction wheels, which also are used for attitude control. The redundant set represents an identical set of eight thrusters.
This marks only the second time during Cassini's 11 years of flight that engineering teams have decided to go to a backup system. Almost all Cassini engineering subsystems have redundant backup capability.
Cassini has already completed its original four-year planned mission, and is currently in extended mission mode. Plans are underway for a proposal to add even more years to the spacecraft's life by extending its tour through 2017.
NASA's budget currently includes about $80 million a year to continue the spacecraft's operations and science.
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