Artist’s depiction of twin spacecraft (Ebb and Flow) that comprise NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission. Image credit: NASA/JPL.
his image shows the variations in the lunar gravity field as measured by NASA’s Gravity Recovery and Interior Laboratory (GRAIL). The gravity field map reveals an abundance of features never before seen in detail, such as tectonic structures, volcanic landforms, basin rings, crater central peaks and numerous simple, bowl-shaped craters. Credit: NASA/JPL-Caltech/MIT/GSFC.

The NASA twin probes GRAIL is on a crash course to hit the lunar surface on December 17. These two tiny probes will smash into the Moon on Monday after having spent months gathering data from Lunar orbit.

Launched September 10, 2011

The Gravity Recovery and Interior Laboratory (GRAIL for short) is a NASA lunar science mission which uses high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraft GRAIL A (Ebb) and GRAIL B (Flow) were launched on September 10, 2011.

Project manager David Lehman of NASA’s Jet Propulsion Laboratory said to AFP “We’re not expecting a big smash, a big explosion,”,  “Their fuel tank will be empty and they are the size of a washing machine.”.

Small but Fast

Ebb and Flow are set to end their controlled descent on a mountain near the Moon’s north pole at about 22:28 GMT. And will hit the surface at 1,7 kilometers per second or 75 600 km/h (3760 miles per hour).

They are being destroyed after having used up all fuel and going into to lower and lower orbit to continue their mission.

The mission has been a great success and managed to generate the highest resolution gravity map ever gathered from another planet or satellite body.

Lehman adds, “Our lunar twins may be in the twilight of their operational lives, but one thing is for sure. They are going down swinging,”. “Even during the last half of their last orbit, we are going to do an engineering experiment that could help future missions operate more efficiently.”.

GRAIL Mission Page