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Satellite Twins Slam Into Moon After Mapping Its Gravity


The twin spacecraft of NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission has slammed into a two kilometer-high mountain near the moon's North Pole, marking the end of its successful endeavor to map the moon's gravity.

The two washing-machine-sized spacecraft, named Ebb and Flow, hit the flank of the mountain about 30 seconds apart as planned at 5:28:51 p.m. EST and 5:29:21 p.m. EST on Monday at a speed of 3,760 mph, the U.S. space agency said in a press release.

Navigators on the GRAIL team had designed an end of mission plan that rules out the extremely remote possibility of either of the two spacecraft impacting near any of the historic "lunar heritage sites."

NASA named the site where the spacecraft impacted the moon in honor of the late astronaut, Sally K. Ride, who was America's first woman in space and a member of the Probes' mission team. The location of the Sally K. Ride Impact Site is on the southern face of an approximately 1.5-mile-tall mountain near a crater named Goldschmidt.

Ride, who died in July after a 17-month battle with pancreatic cancer, led GRAIL's MoonKAM (Moon Knowledge Acquired by Middle School Students) Program through her company, Sally Ride Science, in San Diego.

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. Imaging targets were proposed by middle school students from across the country and the resulting images returned for them to study.

Last Friday, before their final flight, Ebb and Flow were commanded to descend into a lower orbit. Fifty minutes prior to impact, the spacecraft fired their engines until the propellant was depleted. The maneuver was designed to determine precisely the amount of fuel remaining in the tanks to 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 (JPL) in Pasadena, California. "It was one final important set of data from a mission that was filled with great science and engineering data," he added.

The mission team deduced that much of the material aboard each spacecraft was broken up in the energy released during the impacts. Most of what remained probably is buried in shallow craters. The craters' size may be determined when NASA's Lunar Reconnaissance Orbiter returns images of the area in several weeks.

Launched in September 2011, Ebb and Flow had been orbiting the moon since January 1, 2012, during which they returned some remarkable data. 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. The map will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

Scientists have reportedly received new insights into the Moon's structure and history. The mission has found that the crust of Earth's neighboring planet is much thinner than what was believed before, BBC quoted GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge as saying.

"We will miss our lunar twins, but the scientists tell me it will take years to analyze 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 added.

JPL manages the GRAIL mission for NASA's Science Mission Directorate in Washington. GRAIL is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft.

by RTTNews Staff Writer

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