The final satellite needed to complete China’s own navigation and positioning satellite system has passed final on-orbit tests. The completed independent system provides military and commercial value while also facilitating new technologies and services.
The Beidou was launched on a Long March 3B rocket from the Xichang Satellite Launch Center in a hilly region of Sichuan province at 01:43 UTC on Tuesday, 23 June. The satellite was sent into a geosynchronous transfer orbit before entering an orbital slot approximately 35,786 kilometers in altitude which keeps it at a fixed point above the Earth.
Like GPS, the main, initial motivation for Beidou was military. The People’s Liberation Army did not want to be dependent on GPS for accurate positioning data of military units and weapons guidance, as the U.S. Air Force could switch off open GPS signals in the event of conflict.
As with GPS, Beidou also provides and facilitates a range of civilian and commercial services and activities, with an output value of $48.5 billion in 2019.
Twenty four satellites in medium Earth orbits (at around 21,500 kilometers above the Earth) provide positioning, navigation and timing (PNT) services. The satellites use rubidium and hydrogen atomic clocks for highly-accurate timing that allows precise measurement of speed and location.
Additionally, thanks to a number of satellites in geosynchronous orbits, Beidou provides a short messaging service through which 120-character messages can be sent to other Beidou receivers. Beidou also aids international search and rescue services. Vessels at sea will be able to seek help from nearby ships in case of emergency despite no cellphone signal.
The Beidou satellite network is also testing inter-satellite links, removing reliance on ground stations for communications across the system.
Beidou joins the United States’ GPS and Russia’s GLONASS in providing global PNT services, with Europe’s Galileo soon to follow. These are all compatible and interoperable, meaning users can draw services from all of these to improve accuracy.
“The BeiDou-3 constellation transmits a civil signal that was designed to be interoperable with civil signals broadcast by Galileo, GPS III, and a future version of GLONASS. This means that civil users around the world will eventually be getting the same signal from more than 100 satellites across all these different constellations, greatly increasing availability, accuracy, and resilience,” says Brian Weeden, Director of Program Planning for Secure World Foundation.
“This common signal is the result of international negotiations that have been going on since the mid-2000s within the International Committee of GNSS (ICG).”
The rollout of Beidou has taken two decades. The first Beidou satellites were launched in 2000, providing coverage to China. Second generation Beidou-2 satellites provided coverage for the Asia-Pacific region starting in 2012. Deployment of Beidou-3 satellites began in 2015, with Tuesday’s launch being the 30th such satellite.
But this is far from the end of the line. China wants to establish a ‘ubiquitous, integrated and intelligent and comprehensive’ national PNT system, with Beidou as its core, by 2035, according to a white paper.
Chinese aerospace firms are also planning satellite constellations in low Earth orbit to augment the Beidou signal, improving accuracy while facilitating high-speed data transmission. Geely, an automotive giant, is now also planning its own constellation to improve accuracy for autonomous driving.
Although the space segment is complete, China still has work to do on the ground to make full use of Beidou, according to Weeden.
“It’s not just enough to launch the satellites; you also have to roll out the ground terminals and get them integrated into everything you want to make use of the system. Doing so is often much harder and takes much longer than putting up the satellites.
“So, for the Chinese military to make use of the military signals offered by BeiDou-3, they need to install compatible receivers into every plane, tank, ship, bomb, and backpack. That will take a lot of time and effort,” Weeden states.
With the rollout of Beidou satellites complete, inhabitants downrange of Xichang will be spared any further disruption and possible harm. Long March 3B launches of Beidou satellites frequently see spent rocket stages fall near or on inhabited areas. Eighteen such launches have been carried out since 2018.
The areas calculated to be under threat from falling boosters were evacuated ahead of time for safety. Warnings about residual toxic hypergolic propellant were also issued. But close calls and damage to property were all too common.