It is probably no coincidence that modules for China's planned space station will be similar in size to powerful reconnaissance satellites. Rockets designed for one can launch the other. For the same reason, a new factory at Tianjin to build 6-8 outsize spacecraft a year has a clear military role.

The plant's best-known products will be modules for the space station that China plans to build around 2020, but another product line will be “large remote-sensing satellites.” The big spacecraft from Tianjin will join smaller payloads in a launch program that envisages sending up 30 rockets annually over the next seven years, more than doubling the rate of recent years.

Apart from assembly, the factory will be able to test its products, says the government of Tianjin, which is pushing hard to build itself up as one of China's top aerospace centers. Another facility in the city will build launcher rockets China is developing to replace and supplement its old hydrazine-fueled Long March series.

The city's economics and information committee says when the spacecraft plant is complete, it “will be able to build 6-8 outsize spacecraft a year, satisfying requirements for the space station, outsize [communications] satellites, large remote-sensing satellites, large unfolding precision structures and so on.”

The “large remote-sensing satellites” will presumably be military reconnaissance spacecraft. Representatives of the headquarters-level General Armaments Department, which along with the General Staff Department controls China's military satellites, attended the factory's foundation-laying ceremony in September, state media reported at the time. There was no mention of the air force, a sign that its ambitions to take over space operations continue to be rebuffed.

The new launcher family is related to the space station effort, since its largest member, the Long March 5, will be needed to loft modules. No hydrazine-fueled Long March has adequate throw weight, though the standard launcher for the manned space program, the Long March 2F, put the unmanned Tiangong 1 orbital laboratory into orbit in 2011.

Tiangong 1 had a launch mass of 8.5 tons and a diameter of 3.35 meters (11 ft.); the Tianjin plant is presumably needed for larger sizes. A planned cargo craft will also be 3.35 meters across and therefore could also be made at the current facilities of spacecraft builder CAST. But the space station will be built in three modules and have a mass of 60 tons, about 20 tons per module.

And big reconnaissance satellites? No specifications are available from the U.S. National Reconnaissance Office, let alone the General Armaments Department, but the Delta IV Heavy launcher, which is used for such missions, can throw 13 tons to geosynchronous transfer orbit or 23 tons to low Earth orbit (LEO). The largest version of the Long March 5 is designed to lift 25 tons to LEO.

Official drawings show that the Chinese space station's modules will be broader than the cargo craft; quite possibly they will have the Long March 5's 5-meter diameter and therefore use much of its precision manufacturing equipment. That may be one reason the facility is being built in Tianjin. Another reason, as in the Long March 5 program, may have been the port city's access to sea transport to the new launch base under construction on the southern island of Hainan.

The 100,000-sq.-meter (1.08 million-sq.-ft.) spacecraft assembly plant will be substantially complete this August but not ready to begin operations until a year later. It is supposed to satisfy requirements for the next 15-20 years. Since the first Long March 5 is due to fly next year, the factory construction has clearly been timed to fit with the availability of the new launch capability.

The plant's test facilities will attend to the thermodynamic and mechanical properties of spacecraft, their electrical leaks and electromagnetic compatibility, state media report.

CAST has invested in building the factory. As is common elsewhere in the Chinese aerospace and commercial aviation industry, the local government is probably putting up quite a lot of the money. A defense budget contribution is also possible. CAST is a part of national space industry group CASC, which comes under the bureau responsible for defense science and technology industries.

CASC says has averaged 14 launches annually for the past five years and will make 16 this year, lofting 20 spacecraft. They will include the Shenzhou 10 mission, which will complete docking trials China is undertaking in advance of building the space station, and Chang'e 3, which will deploy a lander and rover in a soft landing on Moon. But for the remainder of the decade the launch rate will soar to an average of 30 a year, which CASC reckons will account for about 30% of the global total. By 2020, China will have more than 200 satellites in orbit, about 20% of the total.