Running low on fuel and with a successful moon-mapping mission behind them, NASA’s twin GRAIL probes will leave lunar orbit and crash into the moon on Dec. 17.
The spacecraft will smash into an unnamed crater’s ridge near the moon’s north pole, NASA announced today. The endgame will begin tomorrow morning when the team will send commands to the spacecraft to target the polar site and impact the mountain at roughly 1 mile per second.
Even though the mission’s end is going according to plan, some team members are still disappointed to see it happen.
“I’m hoping tonight, a gas station will pull up next to our spacecraft, refuel it, and we can continue on for another six months,” said GRAIL project manager David Lehman of JPL. “The mission is almost over. It’s kind of sad for me. I think our team’s done an outstanding job.”
Launched in September 2011, the two washing machine-size probes slipped into lunar orbit during the New Year. Since then, the twins — named Ebb and Flow — have been chasing one another around the moon, mapping its gravity field, and sometimes dipping down to within a couple of miles of the lunar surface.
The mission has already been a smashing success. Just last week, the GRAIL team shared the most detailed map yet of the moon’s gravity field – it’s the best map of any gravity field, ever – and revealed a few surprises about the moon’s crust and early history: The moon survived a long, sustained beating that pulverized its crust; less dense than imagined, the moon’s crust and composition support a popular theory describing its formation from a giant impact between Earth and a Mars-size object; and finally, magma intrusions deep in the crust suggest that in its first billion years or so, the moon expanded by as much as 6 miles before shrinking.
The twins, named Ebb and Flow, will join a number of other has-been spacecraft on the lunar surface. Ebb will impact first, and Flow will follow about 30 seconds later. Scientists chose the landing site in part to avoid historical heritage sites associated with such programs as Apollo, Surveyor, Luna, and Lunokhod.
“The impacts are going to occur in the dark, so we will not have live images,” said GRAIL principal investigator Maria Zuber of MIT. But the Lunar Reconnaissance Orbiter will be on line to look at the crash site. “We’re not expecting a flash that is visible from Earth. But nonetheless, LRO, which has extremely, extremely sensitive instruments, will attempt to make some observations.”
NASA's Lunar Orbiters Preparing to Crash Into Moon
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NASA's Lunar Orbiters Preparing to Crash Into Moon
