All launch activities had been put on hold after two failures in June and July that have delayed Beijing’s ambitious space programme, which includes lunar exploration.
The three Yaogan-30 satellites were launched from a centre in Sichuan province. They will join a larger probe launched in May last year to form a constellation to “monitor electromagnetic signals” and other unspecified missions, state news agency Xinhua reported.
The satellites are capable of intercepting radio signals from communications on Earth. They could also pick up the electromagnetic pulses generated by a nuclear explosion to gather intelligence after a thermonuclear weapon test, according to scientists.
But the mission and technical details of the satellites was not disclosed.
“These are military assets – they are not for civilian use, there’s no access,” said Li Xiaoming, a researcher at the Institute of Remote Sensing and Digital Earth at the Chinese Academy of Sciences in Beijing.
The Yaogan satellites are owned and operated by the People’s Liberation Army. The Chinese military has carried out more than 30 launches of the satellites since 2006, according to state media reports.
In the past, official announcements have listed civilian applications for the probes such as land use analysis and disaster relief, but this time there was no mention of any civilian uses.
They were developed by the Micro-Satellite Research Institute at the Chinese Academy of Sciences in Shanghai, according to Xinhua.
They are “just the first batch” of a number of similar satellites being developed for a planned global surveillance network, according to a researcher familiar with the project.
Equipped with cutting-edge sensors, the small satellites orbit the Earth in large numbers and at relatively low altitudes – meaning they can take continuous, high-definition images and pick up extremely faint signals, a job previously done by bigger satellites, the researcher said.
China was also developing large reconnaissance satellites, the researcher said, some of them equivalent to the biggest spy satellites of the United States.
But problems with the Long March rocket have delayed their launch.
The new Long March-5 heavy-lift launch vehicle lost power and plunged into the Pacific Ocean in July, taking with it China’s largest communications satellite.
That came just weeks after the unsuccessful launch of the Long March-3B due to a technical glitch in June.
Tian Yulong, secretary general of the China National Space Administration, told an international space conference in Beijing early this week that they had yet to determine what went wrong during the July launch.
Chinese space scientists and engineers have identified the cause of previous failures within weeks and sometimes hours of the malfunction. This time, months on, the authorities have yet to provide any details.
More than 80 per cent of the technology used in the Long March-5 – China’s biggest and most sophisticated rocket – was new, according to state media reports.
Tian said the team hoped to determine the cause of the problem by the end of this year. All space flights requiring heavy-lift launch vehicles would be delayed, including its mission to build a space station, he added. Stephen Chen, South China Morning News