For the NASA team tasked with the latest lunar mission, New Year's Day seems like Groundhog Day. Twenty-four hours after a probe safely entered orbit around the moon, its twin was poised to do the same on Sunday.
The moon has come a long way since Galileo first peered at it through a telescope. Unmanned probes have circled around it and landed on its surface. Twelve American astronauts have walked on it. And lunar rocks and soil have been hauled back from it.
Four decades after landing men on the moon, NASA is returning to Earth's orbiting companion, this time with a set of robotic twins that will measure lunar gravity while chasing each other in circles.