For years, the official line on China's robot lunar program was a simple case of 1-2-3. There would be an orbiter (Chang'e 1) followed by a lander bearing a rover (Chang'e 2), and finally, a robot lander with a sample return rocket (Chang'e 3).

Prior to late 2007, that was the plan regularly published in Chinese media sources. Shortly before the launch of Chang'e 1 in 2007, China's first lunar orbiter, the story began to change. China officially revealed that a back-up spacecraft had been assembled, ready to fly in case Chang'e 1 failed. In reality, Chang'e 1 flew a highly successful mission, giving China a solid foothold in lunar exploration.

This meant that China had a spare spacecraft. Subsequently, China announced plans to launch the back-up orbiter on an independent mission, to expand on the discoveries of Chang'e 1.

The new mission was dubbed Chang'e 2. Its launch on China's national day (October 1) went smoothly. If the performance of the first mission is any guide, we can expect a satisfying set of outcomes from this orbiter over the course of its six-month mission.

The numerical designations of the landers underwent a short-term reshuffle. The rover-lander was now dubbed Chang'e 3 and the sample-return mission was Chang'e 4.

But there seem to be more missions planned than this. Evidence in the Chinese media increasingly supports the concept that China plans at least four lunar landers.

In an earlier article this year (China's Lunar Twins, SpaceDaily August 19, 2010), I drew attention to a small fact table published in the Global Times, a state-run newspaper aimed at an international audience. The table spoke of Chang'e 3 and 4 as being part of the second stage, or "landing" missions and Chang'e 5 and 6 as the third stage, or "returning". Despite this, the article that accompanied the table did not explicitly state that four landers were being planned. The evidence was intriguing, but tentative.

Recently, China Daily has supplied more evidence for the four-lander plan. Like the table published in the Global Times, three missions are included in the "second stage" of lunar exploration, previously identified as landing without returning. These are Chang'e 2, 3 and 4.

By itself, this yields little insight, but the article then goes on to say that "Chang'e 4 will be a backup satellite for Chang'e 3." This suggests that both spacecraft are mostly identical, and both are landers bearing rovers. Chang'e 2 is technically and orbiter, but it will perform very low sweeps across the lunar surface. This will allow landing sites to be inspected, and also give engineers practice in making a spacecraft descend to a near-landing trajectory.

China Daily makes no mention of Chang'e 5 or beyond. However, the new information dovetails precisely with the earlier data, and offers no contradictions to the idea that Chang'e 5 and 6 are both sample-return missions.

We can expect that a similar strategy to the orbiters is being played out. Two identical spacecraft will be built simultaneously. One will be launched as the primary spacecraft. If it fails, the second spacecraft will be outfitted with the primary set of scientific instruments, then launched on a repeat of the first mission.

If the primary mission succeeds, there will be a review of its performance, and the planning of a second mission. The next flight will probably carry a different set of instruments, and perform different tasks.

China will also probably elect to wait at least a year before launching the second lander. This will allow time to evaluate the scientific data from the first mission, and make plans to build on it.

We can see how this approach was used with Chang'e 1 and 2. Chang'e 2 was converted from being a mere backup for the first spacecraft to something different. Chang'e 2 was outfitted with a high-resolution camera, in addition to other changes. There were alterations to its trajectory to the Moon and its planned orbit.

These changes from the first mission have been so extensive that the Long March 3A rocket, used for the first orbiter, can't be used for this second mission! Instead, Chang'e 2 was launched aboard the more powerful Long March 3C.

We expect that the first lander will fly around the year 2012. Chinese media statements have been cautious about the timetable in recent years, suggesting a launch in 2013. However, the case for a 2012 launch seems to be getting stronger. Phrases such as "before 2013" or "around 2012" are appearing. It would seem that the development of the landing platform and its rover are fairly on-track.

The first lander will be launched aboard a Long March 3B rocket, similar to the 3C rocket used to launch the Chang'e 2 orbiter. The Long March 3B resembles a 3C rocket, but it has four strap-on boosters instead of two, and is thus more powerful than the 3C.

It seems fair to expect the next lander to also use this rocket. This assumes, of course, that there has been no significant increase in the lander's payload or size of the rover. If we assume that roughly two years pass before China's second lander is launched, we could expect Chang'e 4, carrying the second rover, to fly around 2014.

China has previously tipped its first sample-return lander to be launched by the Long March 5 rocket, a new, heavy launch vehicle currently under development. This will fly from a new near-equatorial spaceport under construction on Hainan Island.

The Long March 5 hasn't been mentioned much by the media in recent months, fuelling speculation that its development could be going slowly. The new rocket could be held back by anything from technical problems to financial issues. It was originally expected to make its debut in 2014, but it's not clear if it will be ready then.

It seems likely that the sample-return missions are probably too heavy to fly without the use of this new rocket. If this is the case, then the launch times for the second set of landers will be strongly influenced by the readiness of the Long March 5. Chinese statements have placed the sample-return mission as launching anywhere between 2017 to 2020. Hopefully, the Long March 5 will be operational by then.

Dr Morris Jones is an Australian space analyst and author. Email morrisjonesNOSPAMhotmail.com Replace NOSPAM with @ to send email.