Intelligent Machines Lunar Spacecraft Readied for Launch Two NASA probes will chase each other in orbit around the moon to map its gravity. by Brittany Sauser September 7, 2011 Slideshow: A set of twin spacecraft on a mission to map the moon’s gravity is preparing for launch. The mission, called Gravity Recovery And Interior Laboratory (GRAIL), will create the most accurate maps of the lunar gravity field to date. Slideshow: Aerospace engineers from Lockheed Martin are conducting a fuel tank check on one of the GRAIL spacecraft. Slideshow: One of the GRAIL spacecraft is being inspected by technicians. Slideshow: GRAIL is comprised of two spacecraft, GRAIL-A and GRAIL-B. They are being tested inside a thermal vacuum chamber, which subjects the probes to the atmospheric conditions they will experience in space. Slideshow: The two GRAIL spacecraft will fly in formation around the moon, 55 kilometers above the surface, and maintain a distance of 121 to 262 kilometers apart. Slideshow: The spacecraft will use radio links to communicate with each other and to a station on Earth. Here, technicians check the solar arrays on the spacecraft. Slideshow: The $496 million GRAIL mission will improve scientists’ knowledge of the moon’s gravity field by creating a map 100 to 1,000 times more accurate than anything created to date.