China launched a pair of navigation satellites on Monday afternoon, moving closer to building a global network. On Feb. 12, two more navigation and positioning satellites were launched into medium Earth orbits, following the successful launch of a pair of BeiDou satellites on Jan. 11, said Chinese state media. The twin satellites are the fifth and sixth satellites to join the BeiDou-3 family to form a network. They entered orbit more than three hours after launch from the Xichang Satellite Launch Center in southwest China's Sichuan Province. They are now working from a medium Earth orbit thousands of kilometers above the planet, and will operate for at least 12 years in space, according to the China Satellite Navigation Office. Beidou is the world's fourth space-based navigation system, following GPS by the United States, GLONASS by Russia and Galileo by the European Union. Four strap-on boosters and a core stage fueled by hydrazine and nitrogen tetroxide fired for around two-and-a-half minutes. The Long March 3B dropped the spent booster tanks over Chinese territory as the rocket flew southeast from Xichang, and the launcher’s second stage fell into the South China Sea after completing its burn. A third stage engine placed the two Beidou satellites and the Yuanzheng upper stage into a preliminary elliptical orbit. The upper stage engine was programmed to place the twin payloads into a circular orbit approximately 13,700 miles (22,000 kilometers) above Earth. Chinese state media confirmed the launch was a success, and U.S. military tracking data showed the Beidou satellites were orbiting on their planned trajectory inclined 55 degrees to the equator. In 2019 and 2020, China will send six third-generation Beidou satellites into medium Earth orbits, three to inclined geosynchronous satellite orbits and two to geostationary orbits. According to plans from the satellite office, the network will be made up of 35 satellites before the end of 2020－several now in orbit will be decommissioned by then－to give Beidou global coverage.
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