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In Brief

Flying in Formation Around Moon at 5,800 KPH

28 March 2012

Artist's depiction of two GRAIL spacecraft above lunar surface (NASA/Caltech-JPL/MIT)

Ebb and Flow, the twins of NASA’s GRAIL mission, have been painstakingly synched up in altitude and speed while zipping over the craters, mountains, hills and rills of the moon.

The act of two or more aircraft flying together in a synchronized manner is one of the cornerstones of military aviation. But as amazing as the U.S. Navy’s elite Blue Angels or the U.S. Air Force’s Thunderbirds are to behold, they remain essentially landlocked, anchored to the Earth and its tenuous atmosphere. What if you could take the level of precision of these great aviators to, say, the moon?

“Our job is to ensure our two GRAIL spacecraft are flying a very, very accurate trail formation in lunar orbit,” said David Lehman, GRAIL project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We need to do this so our scientists can get the data they need.”

Trail formation means one craft follows directly behind the other. Ebb and Flow, the twins of NASA’s GRAIL (Gravity Recovery And Interior Laboratory) mission, are synched up in altitude and speed while zipping over the craters, mountains, hills and rills of Earth’s natural satellite, as shown in the artist’s conception above.

As the GRAIL twins fly over areas of greater and lesser gravity at 5,800 kilometers per hour, surface features such as mountains and craters, and masses hidden beneath the lunar surface, can influence the distance between the two spacecraft ever so slightly.

The science instrument beaming invisible microwaves back and forth between Ebb and Flow can detect a change in their separation of one-tenth of one micron — one half of a human hair (0.00001 centimeters).

For more on the science behind the Grail mission, and the painstaking work needed to synchronize the two spacecraft, see the NASA press release.