GRAIL moon mission ends with a bang

After dancing around the moon for months, the twin satellites nicknamed Ebb and Flow performed their final number, crashing into the same peak near the lunar north pole and bringing the GRAIL mission to a close.

A cheer went up in the control room at the Jet Propulsion Laboratory in La Cañada Flintridge as Ebb slammed into the mountain about 2:28 p.m. Monday, followed about half a minute later by Flow. The probes were traveling at nearly 3,800 mph and landed an estimated 25 miles apart.

Even as the team clapped and shook hands in the control room, GRAIL project manager David Lehman acknowledged that the moment was bittersweet.

"Today I brought my handkerchief, just in case," he said.

The GRAIL mission spacecraft, each the size of a compact washing machine, were launched in September 2011 to study every bump and pothole in the moon's gravitational field.

"We have essentially collected more than 99.99%" of the data the team had set out to collect, said Massachusetts Institute of Technology geophysicist Maria Zuber, principal investigator for the mission formally known as the Gravity Recovery and Interior Laboratory.

The two NASA spacecraft worked as a team to do so, flying in formation around the moon and logging all the little tugs the gravitational field exerted on their relative speed.

From March to May, Ebb and Flow flew an average of just 30 miles above the lunar surface.