A NASA robotic spacecraft, finishing its lunar mission with a bang, was purposefully crashed on the moon's far side at 3,600 mph, scientists say.

Because of the extreme speed, they say, the space agency's LADEE moon explorer likely vaporized on Friday, April 18, and would have left no debris behind to mark its impact.

"It's bound to make a dent," project scientist Rick Elphic had predicted Thursday.

Launched in September, the Lunar Atmosphere and Dust Environment Explorer completed a 100-day science mission then continued to orbit the moon until controllers began lowering its orbit to prepare to the crash and impact.

During its time orbiting the moon, LADEE studied and analyzed the makeup of the moon's tenuous atmosphere, identifying magnesium, neon, titanium and other elements, and also examined the veil of dust the moon carries, created by micrometeorites that constantly bombard it surface.

LADEE has insufficient fuel to remain in orbit for any length of time beyond its mission period, NASA said, and controllers began some time ago to plan its orbital lowering and eventual crash.

Over a number of decades a large number of satellites and jettisoned spacecraft parts during the Apollo moon program have impacted the surface of the moon; the most recent before LADEE were a crater-observing spacecraft named LCROSS in 2009 and the twin Grail gravity-measuring satellites in 2012.

However, the uncertainty of exactly when -- and where -- LADEE would crash into the moon had controllers on Earth "on edge," Butler Hine, project manager at NASA's Ames Research Center in California, said.

They wanted to be sure LADEE's impact point wasn't anywhere near important historic artifacts moonwalking Apollo astronauts had left behind.

They included then landing sections of the six Apollo lunar modules that touched down on the moon's surface, as well as rovers, plaques and flags -- and of course Neil Armstrong's historic first footprints from 1969.

The LADEE controllers took great pains to make sure the spacecraft didn't "plow into any of the historic sites," Hine said.

NASA announced the demise of the vending machine-sized spacecraft Friday morning, April 18, but said it could take several day to confirm the exact impact point.