GRAIL's Dynamic Moon Duo Set to Impact Lunar Surface Today

On Oct. 14, the lunar twins of NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, Ebb and Flow, each completed a rocket burn that sealed their fate. The burns modified the orbit of the formation-flying spacecraft, carrying the twins lower and lower over the moon’s surface. On Monday afternoon, Dec. 17, at about 2:28 p.m. PST, their moon-skimming will conclude when a portion of the lunar surface – an unnamed mountain near the natural satellite’s north pole – rises higher than their orbital altitude.

The maneuvers began on Oct. 14 at 7:07 a.m. PST when the Ebb spacecraft fired its main engines for 55.8 seconds, changing its orbital velocity by 10.3 mph (4.6 meters per second). Sixteen seconds later, still at 7:07 a.m. PST, the Flow spacecraft began its maneuver, executing a burn 55.4 seconds in duration with a resulting change in orbital velocity of 10.3 mph (4.6 meters per second).

The spacecraft were named Ebb and Flow by elementary school students in Bozeman, Mont., who won a nationwide contest.

Ebb and Flow are being sent purposely into the lunar surface because their low orbit and low fuel levels preclude further scientific operations.

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