The roving days for NASA’s stuck robotic explorer Spirit are likely over after more than six years rolling across the Martian surface, the space agency announced Tuesday.

“This is not a day to mourn Spirit. This is not a day of loss,” said Doug McCuistion, director of NASA’s Mars exploration program, in a teleconference. “Its driving days are likely over, however its contribution will continue.” [...]

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“For GPS to work, the orbital position, or ephemeris, of the satellites has to be known very precisely,” said Chopo Ma of NASA’s Goddard Space Flight Center in Greenbelt, Md. “In order to know where the satellites are, you have to know the orientation of the Earth very precisely.”

To get a stable reference point for global positioning, GPS systems have to turn to something that is stable. The earth is moving, the sun is moving, the stars are moving so what’s stable? Well quasars are so remote they do not seem to be moving relative to earth and our solar system. [...]

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Source: Space.com – click here for full article