PASADENA, Calif. -- A pair of NASA spacecraft tumbled out of orbit around the moon and crashed back-to-back into the surface yesterday, ending a mission that had peered into the lunar interior.

Engineers commanded the twin spacecraft, Ebb and Flow, to fire their engines and burn their remaining fuel. Ebb plunged first, slamming into a mountain near the moon's north pole. Flow followed a half-minute later, aiming for the same target.

By design, the final resting place was away from the Apollo landing sites and other historical moon sites.

After the double impacts, mission chief scientist Maria Zuber of the Massachusetts Institute of Technology said the spot has been named after team member Sally Ride, the first American woman in space, who died earlier this year.

"It's really cool to know that when you look up now at the moon, there's this little corner of the moon that's named after Sally," said Ride's sister, the Rev. Bear Ride, adding that she hoped schoolchildren will be inspired.

As the crash site was in darkness, the final act was not visible from Earth. The Lunar Reconnaissance Orbiter circling the moon will pass over the mountain to photograph the skid marks left by the washing-machine-sized spacecraft as they hit the surface at 3,800 mph.

After rocketing off the launchpad in September 2011, Ebb and Flow took a roundabout journey to the moon, arriving over the New Year's holiday on a gravity-mapping mission.

More than 100 missions have been flung to Earth's nearest neighbor since the dawn of the Space Age, including NASA's six Apollo moon landings that put 12 astronauts on the surface.

Ebb and Flow focused exclusively on measuring the moon's lumpy gravity field in a bid to learn more about its interior and early history. After flying in formation for months, they produced the most detailed gravity maps of any body in the solar system.

Secrets long held by the moon are spilling out. Ebb and Flow discovered that the lunar crust is much thinner than scientists had imagined.

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Data so far also appeared to quash the theory that Earth once had two moons that collided and melded into the one we see today.

Besides a scientific return, the mission allowed students to take their own pictures of craters and other lunar features as part of a collaboration with a science education company founded by Ride, who died in July of pancreatic cancer at age 61.