Article Posted on : - Dec 18, 2012

An artist's depiction of the twin spacecraft (Ebb and Flow) that comprise NASA's Gravity Recovery And Interior Laboratory (GRAIL) mission. A NASA/JPL photo

WASHINGTON (PTI): NASA's Ebb and Flow gravity mapping satellites have ended their successful mission to the Moon, climaxing with a well-orchestrated crash onto a crater's rim.

The lunar surface where they crashed will be named after Sally Ride, America's first woman in space, who passed away earlier this year, NASA said in a statement.

Ebb and Flow, the two spacecraft comprising NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission were, last Friday, commanded to descend into a lower orbit that would result in an impact on a mountain near the Moon's north pole.

A year after their arrival on the Moon, the formation-flying duo hit the lunar surface as planned at 5:28:51 pm EST and 5:29:21 pm EST respectively at a speed of 1.7 kilometres per second.

The location of the Sally K Ride Impact Site is on the southern face of an approximately 2.5-kilometre tall mountain near a crater named Goldschmidt.

"Sally was all about getting the job done, whether it be in exploring space, inspiring the next generation, or helping make the GRAIL mission the resounding success it is today," said GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge.

"As we complete our lunar mission, we are proud we can honour Sally Ride's contributions by naming this corner of the Moon after her," she said.

The impact marked a successful end to the GRAIL mission, which was NASA's first planetary mission to carry cameras fully dedicated to education and public outreach.

Along with its primary science instrument, each spacecraft carried a MoonKAM camera that took more than 115,000 total images of the lunar surface.

Fifty minutes prior to impact, the spacecraft fired their engines until the propellant was depleted. The manoeuvre was designed to determine precisely the amount of fuel remaining in the tanks. This will help NASA engineers validate computer models to improve predictions of fuel needs for future missions.

"Ebb fired its engines for 4 minutes, 3 seconds and Flow fired its for 5 minutes, 7 seconds," said GRAIL project manager David Lehman of NASA's Jet Propulsion Laboratory.

Launched in September 2011, Ebb and Flow had been orbiting the Moon since January 1, 2012. The probes intentionally were sent into the lunar surface because they did not have sufficient altitude or fuel to continue science operations.

Their successful prime and extended science missions generated the highest resolution gravity field map of any celestial body.

"We will miss our lunar twins, but the scientists tell me it will take years to analyse all the great data they got, and that is why we came to the Moon in the first place," Lehman said. "So long, Ebb and Flow, and we thank you," he said.