Ebb and Flow, the Twin Gravity Recovery and Interior Laboratory (GRAIL) Space Ships, which have been employed to provide detailed gravitational mapping of the Moon’s geology, have apparently served their purpose and will be reprogrammed in a few hours from now to crash into the moon on Monday.

PASADENA, Calif. — Twin lunar-orbiting NASA spacecraft that have allowed scientists to learn more about the internal structure and composition of the moon are being prepared for their controlled descent and impact on a mountain near the moon’s north pole at about 2:28 p.m. PST (5:28 p.m. EST) Monday, Dec. 17.

“Controlled Descent” means “Crash Into the Moon.” At least they might have one final glimpse of Moon Santa before their fateful demise.

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. The map will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

NASA has one hell of a retirement policy. Take note future Space Robots!

“It is going to be difficult to say goodbye,” said GRAIL principal investigator 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.”

If this is what they do to the “exemplary” Space Robots, I’d hate to see what becomes of the slackers.

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.

That’s “Goldschmidt” as in “Hermann Goldschmidt, a nineteenth century astronomer and painter famous for discovering a bunch of asteroids. I don’t think he saw this coming.

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.

Clearly, it is not a good idea to name farm animals or Space Robots.

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.

Whut?

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.

So, their last job is to be a pair of glorified gas station inspectors.

“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.

That’s interesting. So it’s going to be more of a Wiley Coyote thing, then.

“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.”

Boys and their toys.

The NASA press report is here.