NASA has a free
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Here's the description:
NASA’s GRAIL mission is comprised of a pair of mirror-identical spacecraft to the Earths Moon to perform precision gravity measurements. The gravity field will allow scientists to determine the structure of the Moon’s interior from the surface to the deep interior, advance our understanding of the thermal evolution of the Moon and our understanding of how other rocky planets in the solar system are formed.
The GRAIL spacecraft are scheduled for launch on September 8th 2011 aboard the Delta II Heavy rocket from Kennedy Space Center. The voyage to the moon will take approximately 5 months at which point the two spacecraft will enter precision formation orbit ranging from 50km to 200km above the moons surface.
In addition to the gravity measurements the GRAIL Mission also carries the MoonKAM payload, operated by Sally Ride Sciences, which will engage middle schools across the country in the GRAIL mission lunar exploration. Tens of 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 (MOC).
Photos of the target areas will be sent back by the GRAIL satellites and made available in the Images section of this Web site. Students will use the images to study lunar features such as craters, highlands, and maria while also learning about future landing sites.
This app has specific information about the science and purpose of the GRAIL Mission, and features daily mission news updates, images of the spacecraft during assembly and testing, videos and a countdown timer to launch. Later versions of the app will include images captured by MoonKAM