Ebb and Flow, the Gravity Recovery and Interior Laboratory (GRAIL) mission probes, are being sent purposely into the lunar surface because their low orbit and low fuel levels preclude further scientific operations. The duo's successful prime and extended science missions generated the highest-resolution gravity field map of any celestial body, providing a better understanding of how Earth and other rocky planets in the solar system formed and evolved.
Maria Zuber of the Massachusetts Institute of Technology in Cambridge. "Our little robotic twins have been exemplary members of the GRAIL family, and planetary science has advanced in a major way because of their contributions."
The mountain where the two spacecraft will make contact is located near a crater named Goldschmidt. Both spacecraft have been flying in formation around the moon since Jan. 1, 2012. They were named by elementary school students in Bozeman, Mont., who won a contest. The first probe to reach the moon, Ebb, also will be the first to go down, at 2:28:40 p.m. PST. Flow will follow Ebb about 20 seconds later.
Both spacecraft will hit the surface at 3,760 mph (1.7 kilometers per second). No imagery of the impact is expected because the region will be in shadow at the time.
Ebb and Flow will conduct one final experiment before their mission ends. They will fire their main engines until their propellant tanks are empty to determine precisely the amount of fuel remaining in their tanks. This will help NASA engineers validate fuel consumption computer models to improve predictions of fuel needs for future missions.
"Our lunar twins may be in the twilight of their operational lives, but one thing is for sure, they are going down swinging," said GRAIL project manager David Lehman of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Even during the last half of their last orbit, we are going to do an engineering experiment that could help future missions operate more efficiently."
Because the exact amount of fuel remaining aboard each spacecraft is unknown, mission navigators and engineers designed the depletion burn to allow the probes to descend gradually for several hours and skim the surface of the moon until the elevated terrain of the target mountain gets in their way.
The burn that will change the spacecrafts' orbit and ensure the impact is scheduled to take place Friday morning, Dec. 14.
"Such a unique end-of-mission scenario requires extensive and detailed mission planning and navigation," said Lehman. "We've had our share of challenges during this mission and always come through in flying colors, but nobody I know around here has ever flown into a moon mountain before. It'll be a first for us, that's for sure."
During their prime mission, from March through May, Ebb and Flow collected data while orbiting at an average altitude of 34 miles (55 kilometers). Their altitude was lowered to 14 miles (23 kilometers) for their extended mission, which began Aug. 30 and sometimes placed them within a few miles of the moon's tallest surface features.
|The published impact coordinates for the GRAIL twins has been well-surveyed by the Lunar Reconnaissance Orbiter Camera (LROC), at least nine times at high-resolution. LROC QuickMap 125 meter resolution [NASA/GSFC/Arizona State University].|
For more information about GRAIL, visit: http://grail.nasa.gov and http://www.nasa.gov/grail.
Will they be collecting data until the bitter end?
Is the mountain where they will crash a volcano? The crater on top of the right-hand peak looks suspiciously like one.
Hmmm...26.63E? Guess it'll be crashing somewhere south of crater Euctemon then. Haha...good one :)
Note that the text box in the top image gives the longitude as east when it should be west!
The ironic part about those coordinates is they were the only part of the NASA graphic I ended up using, and, having noted their error, I compounded it by using it anyway!
Never underestimate the value of a good night's sleep!
While resembling a volcano, very little else other than the location of the ancient crater is characteristic of the Moon's volcanism elsewhere. Instead, it appears to be very ancient anorthosite bed that, on first glance, seems to carry the grooving of the Imbrium basin forming impact.
The coordinates' mistake obviously isn't yours as they were generally used, 'cross-wise', throughout all of the media reports. The blame, of course, lies with NASA...sometimes the reports know little of the Moon, and so are, wel, generally incorrect.
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