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- Chinese satnav system allows ground team to maintain contact with hypersonic vehicle during rapid evasion manoeuvres, says paper
- BeiDou ‘hotline’ has a time delay of less than a second, theoretically allowing Beijing to call off the strike at the last minute: researchers
A Chinese satellite navigation system will allow the Chinese military to monitor, or even control, a hypersonic flight from China to the United States, according to a new study by Chinese space scientists.
BeiDou is a satellite positioning system similar to GPS that also offers a communication service with global coverage.
In the study, the Chinese researchers simulated the flight of a hypersonic vessel launched from Jinan, in China’s eastern Shandong province, to New York via the Arctic Ocean.
Although China has put several satellite communication networks in orbit, the researchers found that only BeiDou allowed the command centre back on Earth to maintain contact with the hypersonic vehicle while it made wild manoeuvres in the high atmosphere to evade air-defence systems.
The BeiDou “hotline” had a time delay of less than a second, theoretically allowing Beijing to control the flight down to the last minute, the research team said.
These findings “will inspire some engineering applications”, said spacecraft communication researcher Li Shenyang, of the China Aerospace Science and Technology Corporation, in a paper published in the domestic peer-reviewed journal Electronic Design Engineering last week.
Maintaining communication with a hypersonic vessel in flight is no easy task. China’s global communication satellite systems, such as Tiantong and Tianlian, are considerably smaller in scale and coverage area compared with SpaceX’s Starlink.
Only BeiDou, currently comprising more than 50 positioning satellites equipped with microwave and laser communication devices – including 30 satellites for communications – could support an intercontinental flight in near space between any two locations on Earth, according to calculations by Li’s team.
The flight attitude of hypersonic vessels differs from that of a traditional ballistic missile, with changes to attitude, such as roll and pitch, affecting the antenna’s receiving angle. As a result, a hypersonic weapon has to switch its communications frequently from one satellite to another.
Heat also poses a challenge as the surrounding air is ionised because of the high temperature and pressure that form a shell known as plasma sheath. The shell potentially reflects electromagnetic waves to cause a communication blackout during the flight.
By optimising signal transmitters and designing new satellite-jumping methods, Li and his team say they have solved those problems to simulate flight from Jinan, the headquarters of the People’s Liberation Army Northern Theatre, to the largest American city, New York.
According to the simulation, at least two of BeiDou’s communication satellites are visible to the hypersonic vessel at any given time during the flight. The vessel will select the satellite directly above as its main communication satellite. Several other satellites direct their antenna beams to the vessel and stand by as an alternative.
When the vessel has a radical attitude adjustment, the computer will calculate and find a new satellite using real-time location. The new inter-satellite link will be established to allow ground control to give the next orders, according to Li’s team.
It is rare for Chinese researchers to openly simulate a direct strike on the US via the Arctic route with hypersonic technology.
Most hypersonic weapons that China has revealed to the public have had a relatively short range. But in some recent experiments the Chinese military has reportedly demonstrated an ability to fly hypersonic glide vehicles around the globe using technologies that other countries, including the US, have struggled to understand because they appeared “to defy the laws of physics”, the Financial Times reported last year.
Taking inter-satellite delay into consideration, the inherent latency of the BeiDou communication system is about a third of a second, according to an estimate by Li’s team. This gives ground control opportunities to guide the flight simultaneously.
Li and his colleagues did not specify how to overcome the blackout issue. But according to some recent studies by other researchers in China, the problem can be solved by putting the antenna at the back of a hypersonic weapon, where the blocking effect of plasma sheath appears to be the weakest.
