Their mission complete, the satellites were commanded to crash into a mountain to avoid the satellites landing on places of historical value like the Apollo landing sites.
The satellites were the size of washing machines.
Both satellites were placed in the same orbit around the Moon. As they flew over areas of greater and lesser gravity, they moved slightly towards and away from each other. The changes in their relative velocity (speed) was measure precisely using the Lunar Gravity Ranging System. Scientists then translated this information into a high-resolution map of the gravitation field.
The mission was called GRAIL (Gravity Recovery and Internal Laboratory). The aim of the mission was to map lunar gravity and to use that information to map interior and thermal history.
One satellite was named Ebb and the other Flow. Ebb and Flow!
The satellites also carried a set of cameras.
On Monday December 17th, 2012, the twin GRAIL satellites Ebb and Flow, that had been orbiting the moon for nearly a year to map out the Moons gravitational field, were guided to crash land on a mountain on the moon. See commentary of the impact:
The GRAIL launched on a DeltaII rocket from Cape Canaveral Air Force Station on September 10, 2011.
- Satellite - A satellite is something that orbits another body. There are natural satellites, for example the Moon which orbits the earth, and human satellites that have been launched.
- Orbit - The curved path, usually elliptical, made by a planet or satellite.
Figure out how much you weight on the moon!