WASHINGTON — NASA’s Gravity Recovery and Interior Laboratory (GRAIL) satellites completed their prime mission May 29 and were placed in hibernation until August when they will be reawakened for three months of extended science operations.

Instruments onboard the Lockheed Martin Space Systems-built satellites were turned off May 29 at 1 p.m. EDT as the craft were 37 kilometers above the Moon’s Sea of Nectar.

NASA launched the twin spacecraft -– dubbed Ebb and Flow – in September from Cape Canaveral Air Force Station aboard a United Launch Alliance Delta 2 rocket. Ebb entered lunar orbit Dec. 31 followed by Flow on Jan. 1. The pair have been studying the Moon from crust to core since March 8.

“GRAIL delivered to Earth over 99.99 percent of the data that could have been collected, which underscores the flawless performance of the spacecraft, instrument and the Deep Space Network,” Maria Zuber, Grail principle investigator at the Massachusetts Institute of technology in Cambridge, said in a statement.

The GRAIL spacecraft will have to endure a partial lunar eclipse on June 4 that will subject them to sudden changes in temperature and while cloaking their solar arrays in darkness. A second eclipse will happen Nov. 28.

In a May 29 press release announcing the completion of Grail’s primary mission that its engineers are not worried about the spacecraft surviving the eclipses.

“Before launch, we planned from GRAIL’s primary mission science to occur between lunar eclipse,” David Lehman, GRAIL project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. “But now that we have flown Ebb and Flow for a while, we understand them and are confident they can survive these eclipses in good shape.”

NASA plans to reactivate the spacecraft Aug. 30 and use the twin probes — dubbed Ebb and Flow — to take an even closer look at the Moon’s gravity field then they did during their first 89 days of science operations. The extended mission is scheduled to conclude Dec. 3.



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