China to launch another BeiDou-3 navigation satellite duo
China is gearing up to conduct its ninth flight of this year (2018) by launching another pair of BeiDou-3 navigation satellites on Thursday, March 29.
The satellites, designated BeiDou-3 M5 and M6, are scheduled to liftoff atop a Long March 3B rocket from the Xichang Satellite Launch Center (XSLC).
Given that two previous BeiDou-3 doublets were launched on January 11 and February 12, China initially targeted March 12 for the liftoff of M5 and M6, in order to keep a one-month time span between the launches. However, Beijing postponed the mission by two and a half weeks, not disclosing what was behind this decision.
Like most Chinese missions, Thursday’s launch is shrouded in secrecy. Beijing has not revealed any details about pre-launch preparations or about the orbital flight’s timeline. Despite the informational embargo, Western observers assume that Thursday’s flight should last a few hours as the payload is designed to reside in a medium-Earth orbit (MEO).
As is usual for MEO missions, the Long March 3B rocket will fly in a configuration that includes a 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 spacecraft into MEO.
The two passengers of Thursday’s mission are based on a newly-developed dedicated satellite bus and weigh about one metric ton a piece. Both satellites have two deployable solar arrays and were designed to be operational for about 12 years. Once deployed, the duo will offer their services from MEO at an altitude of some 13,360 miles (21,500 kilometers), with an inclination of approximately 55.5 degrees.
Named after the Chinese term for the plough or the Big Dipper constellation, the BeiDou (BDS) project was formally launched in 1994. The first BeiDou satellite was sent aloft in 2000. By 2012, a regional network had already begun to take 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.
BeiDou-3 M5 and M6 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).
According to Yang Changfeng, the chief designer of the BeiDou system, BDS plays an important role in telecommunications, transport, forest fire prevention and disaster prevention and relief. He added that 18 BeiDou-3 satellites is scheduled to be launched into space this year.
Chinese media report that BeiDou is expected to provide navigation and positioning services to countries under the “Belt and Road Initiative” (more than 60 countries in Asia, Europe, Oceania and East Africa) by late 2018.
The three-stage Long March 3B rocket that slated for use on Thursday’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.
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