On 1 January 2012, NASA's GRAIL-B spacecraft, the second of the two Gravity Recovery And Interior Laboratory (GRAIL) spacecrafts, successfully entered orbit around the Moon. Its twin, the GRAIL-A spacecraft, entered Moon orbit on 31 December 2011. Working together, GRAIL-A and GRAIL-B will conduct an unprecedented study of the Moon. The mission’s prime object is to map the lunar gravitational field, and probe the internal structure of the Moon.
"NASA greets the new year with a new mission of exploration," said NASA Administrator Charles Bolden. "The twin GRAIL spacecraft will vastly expand our knowledge of our Moon and the evolution of our own planet. We begin this year reminding people around the world that NASA does big, bold things in order to reach for new heights and reveal the unknown."
The GRAILs were placed into a near-polar, elliptical orbit around the Moon. They last a period of approximately 11.5 hours, to orbit the Moon once. Over the coming weeks, the GRAIL team will adjust their orbital period to just under two hours. When the GRAILs begin collecting data, in March 2012, the two probes will be in a near-polar, near-circular orbit with an altitude of about 55 km.
As they orbit the Moon, the GRAILs will transmit radio signals precisely determining the distance between them. When they fly over areas of greater and lesser gravity caused by terrains such as mountains and craters, and masses hidden below the lunar surface, the distance between the two spacecrafts will change slightly.
Scientists will translate these distance measurements into an accurate map of the Moon's gravitational field. The data will allow scientists to better understand the interior structure of the Moon. This information will increase knowledge of how Earth and its neighboring rocky planets evolved into the diverse worlds we see today.
Each of the GRAILs carries a small camera, known as the GRAIL MoonKAM (Moon Knowledge Acquired by Middle school students), only for education and public outreach purposes. GRAIL MoonKAM will engage middle schools across the USA in the GRAIL mission and lunar exploration. Thousands of fifth- to eighth-grade students will select target areas on the lunar surface and send requests to the GRAIL MoonKAM Mission Operations Center. Images of the target areas will be sent back by the GRAILs, for students to study.
References
NASA
www.nasa.gov/
Further Reading
GRAIL Mission
http://www.nasa.gov/grail
MoonKAM
http://solarsystem.nasa.gov/grail/education.cfm