China has made tremendous progress with its lunar exploration program. It has sent two spacecraft to orbit the Moon and has also landed a robot rover on the surface. Later this year, we expect China to take another step forward with its next robotic lunar mission.

For the first time, a Chinese spacecraft will make a round trip. The spacecraft will be launched on a "free return trajectory" which will carry it around the far side of the Moon and back to Earth. As it approaches home, a capsule will separate and parachute to the ground.

The most immediate purpose of this mission is to test gear designed for a future robot lunar mission. China has plans to land a robot on the Moon to retrieve rock and soil samples. These will be loaded aboard a small rocket, which will carry them into lunar orbit.

The samples will be transferred to another spacecraft in lunar orbit, which will then fly them back to China. The capsule to be used on this upcoming mission is a prototype of the design planned for this sample-return mission.

We have been expecting this mission for some time, even though details were somewhat sketchy. It makes sense for the equipment slated for the complex sample-return mission to be tested under actual flight conditions. But photography of the capsule released by the Chinese has hinted at another agenda.

China could be practicing for a mission to launch an astronaut to the Moon and back. The astronaut would also fly a "free-return trajectory" around the far side of the Moon, and would not land there. If China carries out such a mission, it would send a Chinese astronaut further into space than any previous mission. Assuming that it happens before a private circumlunar mission is launched by a US-Russian space partnership, it would also mark the first return of any human to the Moon in more than four decades.

China has given no official word of such a plan, but this is no reason to dismiss the idea. China has always been secretive about its space plans, and seems to be growing even more secretive under its new media censorship policies. Let's not forget that the very existence of its Shenzhou human spacecraft program was a closely guarded secret for years before its first test launch in 1999.

The creation of this test mission was never previously mentioned in the three-stage lunar mission plan that China announced many years ago. We knew of plans to orbit the Moon, land a rover and then send a sample-return mission. We later discovered that there would be two missions of each type. Later, we were told that the sample-return mission would involve a docking with an orbiter in lunar orbit. But the plans for an intermediate circumlunar mission were announced somewhat late, and the mission doesn't even seem to have an official name.

All other lunar missions have been labelled as "Chang'e" flights, with Chang'e-1 and Chang'e-2 representing China's first lunar orbiters, and Chang'e-3 as the first lander. Chang'e-4 is the next robot lander with a rover.

The strange and somewhat veiled publicity surrounding this mission is suspicious, and suggests that it isn't as neatly stovepiped into the robot lunar exploration program as we previously suspected. Another branch of the space program is also involved, and that's probably the astronaut program.

But wait. Plenty of robot spacecraft send capsules back to Earth. They have no connection to human spaceflight. Why should this be any different?

Photography released by China shows that the capsule is a highly accurate copy of the bell-shaped Shenzhou descent module, the very module used to carry Chinese astronauts to Earth. It is much smaller, so small that it would be unsuitable for launching even a single astronaut, but the design is accurate. There are some practical reasons for using this type of bell-shaped system.

It's very stable, has a good interior volume distribution and its engineering properties are well known. Using a bell-shaped module makes sense, but there was no need to reproduce so many exact design elements of the Shenzhou module.

The curious way that this mission has been shoe-horned into a mission schedule that previously did not include it is thought-provoking. The low-key discussions and lack of an official name, or even an official "Chang'e" designation, is also odd. The fact that a scale model of a Shenzhou astronaut capsule is being sent to the Moon and back is too much of a smoking gun to be ignored.

China is clearly doing the groundwork for a future Chinese circumlunar astronaut mission. We don't know when it could happen, but it is realistic to assume that China could carry out such a flight within a decade. Never mind the lack of an official plan. We don't know if this has been planned for years, or if the relatively new Chinese leader Xi Jinping ordered the mission in recent times. Whatever the case, we should remain alert for this upcoming mission. China's lunar plans are more ambitious than the world at large knows.

Dr Morris Jones is an Australian space analyst who has written for spacedaily.com since 1999. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries.