BEIJING — The heaviest and most technologically challenging member of China’s new space launcher family, the Long March 5, has been delayed by at least another year, to 2015, due to challenges in building its structure.

Another launcher, which would improve China’s ability to launch military satellites on short notice thanks to its solid fuel, is due to fly in 2016 under the designation Long March 11, while the industry is also preparing to seek funding for an enormous Moon rocket.

The problem that is holding up Long March 5, with a hydrogen-fueled core first stage and comparable to the U.S. Delta IV, is one long identified by Chinese space engineers: the difficulty in precise manufacturing of its 5 meter (16.4 ft.) dia. body. Propulsion, which usually ranks high in the challenges of space launcher technology, is not mentioned as a problem.

“Our plan has encountered some difficulties” in three recent test failures, Liang Xiaohong, deputy head of the China Academy of Launch Vehicle Technology (CALT), tells the China Daily, an English-language state-mouthpiece newspaper aimed at foreign readers.

The main difficulty is structural, Liang says. “... When an object is bigger, its technical risks and functional defects are also magnified,” he says. The specific challenge is in machining — exactly the issue that Chinese space engineers have spoken of for several years. CALT is pushing manufacturers for better precision.

In 2007, the Long March 5 was due to make its first flight in 2013. A year ago, the target slipped to 2014. The China Daily now says the first flight will “probably” occur in 2015. The launcher is needed to loft the 20-metric-ton modules of China’s manned space station and — as indicated by construction of a factory for outsize spacecraft — big reconnaissance satellites.

Long March 11 will launch much smaller satellites. With solid fuel, it will be ready for firing on short notice, offering the ability to send a reconnaissance spacecraft aloft almost as soon as a tactical need for one arises — for example, to sweep a patch of ocean for enemy ships. Liang describes Long March 11 as having value in civil missions such as post-disaster reconnaissance. But Chinese space officials routinely refer to non-military applications of equipment that have obvious military uses. One official last year said the payload of a then-planned but unnamed solid launcher might be 1 ton.

The second member of the new liquid-propellant Chinese launcher family, Long March 7, has also been delayed. A year ago it was due to fly late in 2013. Now the target is 2014. Liang adds that it may become China’s manned launcher. As such, it would replace the Long March 2F, a member of the hydrazine-fueled Chinese launcher family that dates to the 1960s and should ultimately be superseded by the rocket family now under development.

But the authorities will surely not rush to anoint Long March 7 as their manned launcher. Apart from redundant and more robust systems, it will presumably need a long record of successful unmanned launches before it is trusted to carry people.

The state space industry intends during the current five-year planning period, 2011-2015, to ask the government for approval for development of a launcher for manned Moon missions, the China Daily says in the same report.

Since that planning period is already well under way, the industry must hope to launch full-scale development no earlier than 2016. The Moon rocket, with a diameter of at least 8 meters, would loft 100 tons to low Earth orbit, making it smaller than the U.S. Saturn V used in the 1960s and 1970s. The Tianjin space manufacturing base has been sized for up to 10-meter dia.