Twin NASA probes plunge into lunar mountain on purpose (3)

（Xinhua）  14:41, December 18, 2012

Fifty minutes prior to the impact, the spacecraft fired their engines until the propellant was depleted. The maneuver was designed to determine precisely the amount of fuel remaining in the tanks. This will help NASA engineers validate computer models to improve predictions of fuel needs for future missions.

The mission team has deduced that much of the material aboard each spacecraft was broken up in the energy released during the impacts. Most of what remained probably is buried in shallow craters. The craters' size may be determined when NASA's Lunar Reconnaissance Orbiter returns images of the area in several weeks.

When launched in September 2011, the probes were named GRAIL A and B. They were renamed Ebb and Flow in January in a nationwide contest. Ebb and Flow were placed in a near-polar, near-circular orbit at an altitude of approximately 34 miles (55 km) on Dec. 31, 2011, and Jan. 1, 2012, respectively.