Chinese scientists are developing a family of high altitude airships that can help with Earth observation, maritime monitoring and communication signal relays.

Researchers at the Chinese Academy of Sciences are working on the stratospheric airships, so-called because they are capable of conducting long-term operations in the stratosphere－the second major layer of Earth's atmosphere at an altitude of 20 to 50 km.

According to the academy's development plan for the 13th Five-Year Plan period (2016-2020), which lists 140 research and development priorities, researchers are to develop key technologies and techniques for controllable stratospheric airships and perform flight tests before the end of 2020.

"Our stratospheric airships will come in various sizes, and we have test-flown two of them already," said Wang Yuechao, director of the academy's Bureau of Major Research and Development Programs.

"The latest test took place in August, when we flew an airship and achieved our goals."

He said that almost all of the world's major powers are exploring high-altitude aerospace craft, with China among the top players in the field.

The academy's stratospheric airships can operate autonomously or be remotely controlled by ground personnel, according to earlier reports.

Solar-powered, reusable and unmanned, such vehicles can spend a long time aloft and serve a wide range of purposes. At least five nations, including the United States and Japan, are developing such systems.

Wang Ya'nan, editor-in-chief of Aerospace Knowledge magazine, said that compared with spacecraft and satellites, stratospheric airships do not need a launch pad and are convenient to retrieve and reuse. They also provide a wider view of the Earth and a much longer operational time than aircraft.

"Therefore, they provide a better platform for Earth monitoring and maritime surveillance," Wang said.

Moreover, because airships are closer to the Earth than satellites, they can act as a better hub for relaying communications signals.

"In addition, stratospheric airships are able to carry payloads that will be as much as 10 times that of a spacecraft," Wang said.

Zhu Ming, an associate professor at Beihang University in Beijing, said they could have many uses in the public sector.

"They have a lot of potential in environmental protection, disaster relief and weather forecasting," he said.