China’s BeiDou satellite system more visible from space than its US rival GPS, study finds

Researchers say a spacecraft travelling at or below an altitude of 2,000km would be able to see 50 per cent more from the Chinese constellation
They concluded that the most precise information could be accessed by using a combination of signals from the two navigation systems

China's space programme

Stephen Chenin Beijing

Published: 11:30pm, 23 Feb 2021

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China’s BeiDou satellite navigation system is more visible – and may be more of a beacon for spacecraft – than its US rival GPS from near-Earth space, according to a new study.

Researchers from the National Space Science Centre in Beijing found that a spacecraft travelling at or below an altitude of 2,000km (1,200 miles) would be able to see 50 per cent more BeiDou satellites than those from the Global Positioning System at any given time.

They said the positioning accuracy of the BeiDou signal was also on par with that of GPS because it used ultra-precise atomic clocks.

“It is possible to get global coverage and an all-time positioning service for space applications using the BeiDou satellite navigation system alone,” the team led by Wu Chunjun wrote in a peer-reviewed paper published in the journal Geomatics and Information Science of Wuhan University on Monday.

Precise location information for spacecraft and satellites has traditionally been obtained using tracking stations on the ground – but sometimes there is no ground station.

The information is critical for a space mission since a tiny mistake in positioning could lead to a miscalculation in the orbit of a spacecraft or other problems.

Tracking stations on the ground have traditionally been used to get precise location information for spacecraft and satellites. Photo: Handout

According to the study, China has been using GPS for its space missions for years. Chinese space scientists developed a GPS signal receiver and tracking software to improve its accuracy so that they could locate spacecraft with a margin of error of no more than 3cm.

China started developing its own version in the 1990s because it wanted a navigation system independent of GPS, which is controlled by the United States military. The final satellite of the BeiDou system was sent into orbit last year to complete the network.

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It is becoming more popular – even some of the newer iPhone models use BeiDou services – but not in space. According to the study, that is because some of the satellites launched in the early stage of the network used older technology.

“There were various concerns” about whether BeiDou could be used in space, the paper said.

Wu’s team analysed data collected by a Chinese weather satellite that can receive both GPS and BeiDou signals, to see how accurate the system was. They found that while there were problems with the older BeiDou satellites, when used in combination with the newer ones the performance was significantly better.

But they said the main advantage of the BeiDou system was that considerably more of its satellites were visible to a spacecraft in near-Earth orbit. The number ranged from six to 29 for BeiDou, versus six to 15 for GPS, the study found.

The global coverage could also help China’s military, according to a Beijing-based space scientist who declined to be named due to the sensitivity of the matter. He said BeiDou could be used to pinpoint the location of a long-range missile throughout its flight so it could evade missile defence systems and hit a target.

The space-based navigation system would allow a missile to change course autonomously rather than have its flight path programmed before launch, he added.

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China’s space assets are increasing as it pushes ahead with an ambitious programme. It plans to start building an orbital space station in the coming months, while cutting-edge satellites to detect extremely weak signals – from gravitational waves to submarines lurking 500 metres under water – are also under development. The Beijing space scientist said many of these new projects could use BeiDou’s atomic clocks for altitude control, timing, measurement and other purposes.

However, Wu and his team concluded that the most precise information could be accessed by using a combination of BeiDou and GPS signals. They said a spacecraft equipped with a receiver that worked with both systems would mean more guiding satellites were visible – over North America, for instance, the number could even double.

Future upgrades of signal receivers and software could see the two systems being used together for deep space missions such as journeys to the moon and beyond, the paper said.