China to launch another duo of BeiDou-3 navigation satellites on Sunday
China is gearing up to launch the nation’s latest duo of BeiDou-3 satellites into space atop a Long March 3B rocket on Sunday, February 11.
The mission is currently planned to take to the skies at around 5:10 GMT (0:10 a.m. EST) from the Xichang Satellite Launch Center (XSLC). When launched, it should mark the third flightof a BeiDou-3 doublet in just three months.
The BeiDou-3 M3 and M4 spacecraft, which are being readied for Sunday’s flight, were initially planned to be sent aloft on Jan. 11. However, China decided to send BeiDou-3 M7 and M8 on that day instead of M3 and M4.
Sunday’s mission, like most Chinese missions is shrouded in secrecy as Beijing does not inform the public about pre-launch preparations and does not offer many details regarding the Long March 3B’s flight to orbit.
However, given that the BeiDou-3 M satellites are designed to reside in a medium-Earth orbit (MEO), the flight should last a few hours in order to place the payload into their desired orbital location. If everything goes as planned on Sunday, the Long March 3B rocket will fly in a configuration with the Yuanzheng-1 (YZ-1) upper stage, which is expected to ignite its YF-50D engine some 20 minutes after liftoff and should burn out about six hours into the flight, deploying the two passengers into MEO.
BeiDou-3 M3 and BeiDou-3 M4 are based on a newly-developed dedicated satellite bus and weigh about one metric ton a piece. Both spacecraft have two deployable solar arrays and were designed to be operational for about 12 years. The duo will offer their services from MEO at an altitude of some 13,360 miles (21,500 kilometers), inclined 55.5 degrees.
BeiDou-3 M3 and M4 satellites represent the third phase of the BDS system (BeiDou-3). It is the final stage of the establishment of a Chinese space-based navigation architecture. The constellation should consist of 27 BeiDou-3M satellites in MEO, five BeiDou-3G satellites in a geostationary orbit (GTO), and three BeiDou-3I satellites in an inclined geosynchronous satellite orbit (IGSO).
China’s busy 2018 launch manifest envisions around 35-40 missions, includes 18 BeiDou-3 satellites, according to Yang Changfeng, chief designer of the BeiDou system.
“The intensive launches will pose a great challenge. We must exercise strict control over quality specifications to ensure each of them is a success,” Yang said last month.
Named after the Chinese term for the Plough or the Big Dipper constellation, the BeiDou project was formally launched in 1994. The first BeiDou satellite was not launched until 2000, however. Nonetheless, by 2012, a regional network had already taken shape, which provided positioning, navigation, timing, and short message services in China and several other Asian countries. The first BeiDou-3 satellite was launched in March of 2015.
The three-stage Long March 3B rocket that will be used for Sunday’s flight is a 180-foot (55-meter) tall launch vehicle that is capable of sending up to 12 metric tons of payload to low-Earth orbit or 5 metric tons of cargo into GTO. For some launches, this rocket can be equipped with a Yuanzheng-1 upper stage.
As noted, Sunday’s mission will be the third launch of a BeiDou-3 duo within a time span of three months. On Nov. 5, 2017, China launched BeiDou-3 M1 and M2, while on Jan. 11, 2018 M7 and M8 satellites were sent to orbit.
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