The Spacecraft: Ebb & FlowThe twin GRAIL spacecraft, named Ebb and Flow, launched into space Sept. 10, 2011. After a nearly 4-month journey to the Moon, Ebb arrived in lunar orbit on New Year's Eve and Flow arrived shortly after on New Year's Day.
Although each GRAIL satellite was only about the size of a washing machine, standing 3.58 feet high and 3.12 feet wide, the spacecraft each weighed 677 pounds when fully fueled. Instruments on board the spacecraft included a microwave ranging instrument, accelerometer, and star camera. While in lunar orbit, the GRAIL satellites used energy from the Sun as well as 10 nickel-hydrogen battery cells to power their trip.
The distances traveled by Ebb and Flow to the Moon were similar but not identical. Ebb traveled about 2,594,378 miles to reach the Moon, while it took Flow about 2,663,793 miles. While in lunar orbit, Ebb traveled 13,193,550 miles and Flow traveled 12,800,869 miles.