NASA announced today (December 28, 2011) that two small spacecraft – the twin GRAIL spacecraft launched on September 10, 2011 – are now on their final approach to orbit around the moon.
The main-engine burns that will place them in lunar orbit are scheduled for New Year’s Eve and New Year’s Day 2012.
This ingenious mission will use the moon’s own gravity to study the lunar interior. GRAIL stands for Gravity Recovery And Interior Laboratory (GRAIL). The idea is that the two craft orbit the moon, always maintaining the most precisely equal distance from each other that they can. Little variations in distance between GRAIL-A and GRAIL-B will occur as they fly over areas of greater and lesser gravity. What causes the change in gravity on the moon? Just as on Earth, the slight change in gravity will be caused both by visible features such as mountains and craters – and by masses hidden beneath the moon’s surface.
In fact, those hidden masses – known as “mascons,” for “mass concentrations,” to scientists – are what cause one face of the moon to stay pointed in Earth’s direction. Scientists are itching to learn more about them, because, they say, this knowledge will help us understand how the moon evolved.
As of today, GRAIL-A is 65,860 miles (106,000 kilometers) from the moon and closing at a speed of 745 mph (1,200 kph). It is scheduled to enter orbit beginning at 1:21 p.m. PST (4:21 p.m. EST) for GRAIL-A on December 31, 2011.
GRAIL-B is 79,540 miles (128,000 kilometers) from the moon and closing at a speed of 763 mph (1,228 kph). Its insertion to orbit will begin at 2:05 p.m. PST (5:05 p.m. EST) on Janurary 1, 2012.
Happy New Year moon fans!
Bottom line: GRAIL-A and GRAIL-B – twin NASA spacecraft designed to study the moon using the moon’s own gravity – are on their final approach to lunar orbit. GRAIL-A will begin orbit insertion on December 31, 2011. GRAIL-B will begin orbit insertion on January 1, 2012.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.