Vid NASA's twin lunar-orbiting GRAIL spacecraft are preparing to smash into the surface of the Moon as a final send-off.
The Gravity Recovery and Interior Laboratory (GRAIL) ships, Ebb and Flow, will be intentionally crash-landed on the Moon now that their low orbit and fuel levels have ended their mission abilities.
The crash and burn, scheduled for 22.28 GMT on Monday, will hit a mountain located near the Goldschmidt crater, finishing a mission that start on 1 January this year.
"It is going to be difficult to say goodbye," said GRAIL principal investigator Maria Zuber of MIT. "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 two craft have generated the highest-resolution gravity field map of any celestial body, which will help boffins understand more about how Earth and other rocky planets in the Solar System formed and evolved.
Just before they impact on the Moon, Ebb and Flow will do one final experiment, firing their main engines until their propellant tanks are empty to show NASA scientists exactly how much fuel they have left. This will help engineers to improve predictions about how much fuel missions need.
"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. "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."
Both spacecraft will hit the surface at 3,760mph, with Ebb going down first, followed 20 seconds later by Flow. NASA won't be able to get images of the crash because the mountain will be in shadow at the time of impact.
"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 colours, 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." ®