Washington: A pair of unmanned NASA spacecraft that are orbiting the Moon were renamed Ebb and Flow on Wednesday by a middle school class in Montana, the US space agency announced.

The original names for the twin probes Gravity Recovery and Interior Laboratory (GRAIL) -- A and B -- were not very inspired, admitted principal investigator Maria Zuber of the Massachusetts Institute of Technology.

"We were so busy in the design and getting these two spacecraft launched on time that when we gave them names, we gave them names of A and B, and that isn't too creative. So we asked the youth of America to assist us," she said.

More than 11,000 students took part in the contest to rename the twin craft which aim to map the Moon's surface, determine its gravity field and reveal the contents of its inner core.

The winners were a fourth grade classroom of nine- and 10-year-olds at Emily Dickinson School in Bozeman, Montana.
"They noted the fact that GRAIL is going to be studying gravity on the Moon, and that the effect of gravity on the Earth is seen every day in terms of tides," said Zuber.