On July 25, 2015, the 18th and 19th satellites were successfully launched from the Xichang Satellite Launch Center, marking the first time for China to launch two satellites at once on top of a Long March 3B/Expedition-1 carrier rocket. The Expedition-1 is an independent upper stage capable of delivering one or more spacecraft into different orbits.
During which month of 2007 was the 18th satellite launched?