LOS ANGELES — NASA says its twin spacecraft are on course to arrive back-to-back at the moon after a 3 1/2-month journey.
The space agency said today the probes named Grail-A and Grail-B are poised to slip into orbit around the moon over the New Year's weekend on a mission to study lunar gravity.
The probes launched from the same rocket in September but have been traveling separately to their destination. Though the moon is relatively close at about 250,000 miles away from Earth, the spacecraft took a roundabout journey to save on costs by launching on a small rocket.
Once in orbit, the spacecraft will spend the next two months tweaking their positions before they start collecting data.
The $496 million mission is managed by the NASA Jet Propulsion Laboratory.