BEIJING - China is developing a cargo spaceship to supply the nation's future space station, said Zhou Jianping, chief designer of China's manned space program.

Supply technology is one of the keys to sustaining a space station's operation with regular deliveries of fuel, food and equipment, as well as experimental devices.

"The Soviet Union's Mir space station, which de-orbited in 2001, needed supplies from a cargo ship four times a year. Our cargo spaceship will have more capacity than that, so we will need to make fewer deliveries," Zhou said.

"It is unlikely we will rely on a manned spaceship to ferry food and fuel to a space station, as a manned spaceship can take only 300 kg of cargo, far from enough for future space station operations," he said.

This cargo spaceship, yet unnamed, will weigh 13 tons when fully loaded, Zhou said without elaborating on how much cargo exactly it can carry.

With a diameter of 3.35 meters, it will look like the Tiangong-1 space module that was launched on Thursday as part of China's first spacecraft rendezvous and docking mission. It is a two-module structure - a resource module providing propellant and electricity and another module carrying supplies, he said.

Different from the manned Shenzhou spaceships that transport astronauts between Earth and space, a cargo spaceship will not return to Earth, which will save costs, he said.

At present, a new launch vehicle, Long March VII, is under development for sending the cargo spaceship into space, he said.

China plans to build a 60-ton space station around 2020, made up of three capsules, according to China's manned space program.

Pang Zhihao, a researcher and deputy editor-in-chief of the monthly magazine Space International, said earlier that the space station is rather small compared to the International Space Station (419 tons), and the Mir space station (137 tons).

"But it is the world's third multi-module space station, which usually demands much more complicated technology than a single-module space lab," he said.