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http://www.universetoday.com/99035/end-of-mission-grail-spacecraft-impact-a-mountain-on-the-moon/End of Mission: GRAIL Spacecraft Impact a Mountain on the Moon<br />
by Nancy Atkinson on December 18, 2012<br />
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The planned path of the GRAIL spacecrafts’ final orbit. Credit: NASA<br />
“So long, Ebb and Flow, and we thank you,” said GRAIL project manager<br />
David Lehman of NASA’s Jet Propulsion Laboratory after the twin GRAIL <br />
spacecraft completed a planned formation-flying double impact into the <br />
southern face of 2.5-kilometer- (1.5-mile-) tall mountain on a crater <br />
rim near the Moon’s north pole. Mission team members estimate the two <br />
spacecraft were traveling at a speed of 1.7 kilometers per second (3,760<br />
mph), and likely broke apart on impact. NASA said that most of what <br />
remains of the washing machine-sized spacecraft are probably buried in <br />
shallow craters, and the size of those craters will hopefully be <br />
determined when NASA’s Lunar Reconnaissance Orbiter is able to image the<br />
impact site in about two weeks.<br />
NASA has honored the GRAIL team’s request to name Ebb and Flow’s <br />
impact sites after astronaut Sally Ride, who passed away earlier this <br />
year. She was America’s first woman in space and a member of the GRAIL <br />
mission team.<br />
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A simulation of the GRAIL impacts:<br />
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Impact occurred at 10:28:51 UTC (5:28:51 p.m. EST) and 10:29:21 UTC <br />
(5:29:21 p.m. EST). Right now it is night at the impact site, so <br />
sunlight should return within two weeks, enabling imaging of the site. <br />
LRO also took “before” images of the site during previous daylight <br />
orbits. <br />
The impact marked a successful end to the GRAIL(Gravity Recovery and <br />
Interior Laboratory)mission, which in just a 90-day prime mission <br />
generated the highest-resolution gravity field map of any celestial body<br />
— including Earth — and determined the inner crust of the Moon is <br />
nearly pulverized. <br />
“Ebb and Flow have removed a veil from the Moon,” said GRAIL <br />
principal investigator Maria Zuber during a televised commentary of the <br />
impacts today, adding that the mission will enable discoveries for years<br />
to come. <br />
Data from GRAIL’s extended mission and main science instruments are <br />
still being analyzed, and the findings will provide a better <br />
understanding of how Earth and other rocky planets in the solar system <br />
formed and evolved.<br />
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GRAIL was NASA’s first planetary mission to carry cameras fully <br />
dedicated to education and public outreach. Ride, who died in July after<br />
a 17-month battle with pancreatic cancer, led GRAIL’s MoonKAM (Moon <br />
Knowledge Acquired by Middle School Students) Program through her <br />
company, Sally Ride Science. The camera took more than 115,000 total <br />
images of the lunar surface, and imaging targets were proposed by middle<br />
school students from across the country and the resulting images <br />
returned for them to study.<br />
“Sally was all about getting the job done, whether it be in exploring<br />
space, inspiring the next generation, or helping make the GRAIL mission<br />
the resounding success it is today,” said Zuber. “As we complete our <br />
lunar mission, we are proud we can honor Sally Ride’s contributions by <br />
naming this corner of the Moon after her.”<br />
Last Friday, Ebb and Flow, the two spacecraft comprising NASA’s <br />
Gravity Recovery and Interior Laboratory (GRAIL) mission, were commanded<br />
to descend into a lower orbit that would result in an impact Monday on a<br />
mountain near the Moon’s north pole.<br />
Fifty minutes prior to impact, the spacecraft fired their engines <br />
until the propellant was depleted. The maneuver was designed to <br />
determine precisely the amount of fuel remaining in the tanks. This will<br />
help NASA engineers validate computer models to improve predictions of <br />
fuel needs for future missions.<br />
<br />
Screenshot of engineering data showing trajectory of the two GRAIL spacecraft about 2 minutes before Ebb’s impact. Via NASA TV. <br />
“Ebb fired its engines for 4 minutes 3 seconds, and Flow fired its <br />
for 5 minutes 7 seconds,” Lehman. “It was one final important set of <br />
data from a mission that was filled with great science and engineering <br />
data.”<br />
Launched in September 2011, Ebb and Flow had been orbiting the moon <br />
since Jan. 1, 2012. The probes were intentionally crashed into the lunar<br />
surface because they did not have sufficient altitude or fuel to <br />
continue science operations.<br />
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GRAIL moon probes' crash site named for astronaut Sally Ride<br />
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