In early December, China will land its first robot spacecraft on the surface of the Moon. Shortly after landing, the Chang'e-3 lander will release a six-wheeled rover that will trundle across the regolith.

We've been expecting this rover to land for a long time, as it represents an intermediate step in China's plans to robotically explore the Moon. China has already sent two spacecraft to orbit the Moon, and is now moving on to landings. The third phase of exploration will involve a lander that collects samples of lunar soil and returns them to Earth.

While most Chinese media coverage has focused on the upcoming first lander, it's worthwhile remembering that China has more to come in the near future. There has been little discussion of these plans in recent times, but roughly three years ago, China made signs in its state-run media that it plans a follow-up to the Chang'e-3 mission. China has two Moon rovers in the pipeline.

This fits in with a trend that China seems to be following with its lunar program. Each type of mission has two essentially identical spacecraft built for it. The first spacecraft is placed in the spotlight and given the prime mission.

The second spacecraft waits quietly in the wings, with almost no publicity. If the first mission fails, the second spacecraft can be rolled out fairly quickly to replace its lost twin. If the first mission succeeds, the second spacecraft is assigned to fly a different mission to the first. Either way, good use is made of the backup spacecraft.

China was very coy about admitting the "twin spacecraft" strategy for years, and only revealed that a second lunar orbiter had been built shortly before the launch of the Chang'e-1 spacecraft in 2007. At the time, China stated that the spacecraft was a back-up. Fortunately, Chang'e-1 performed well in its mission. The back-up spacecraft, now labelled Chang'e-2, was launched on a modified mission in 2010.

Going further (literally) than its twin, Chang'e-2 completed a shorter mission in lunar orbit and then flew deeper into space to fly past the asteroid Toutatis. Chang'e-2 also flew a different trajectory to the Moon and used a slightly more powerful launch vehicle.

Let's examine the next pair of twin lunar spacecraft. Although China has not discussed this in recent times, it seems almost certain that there is a back-up lunar lander and rover that is either mostly constructed or fully constructed.

This spacecraft is probably in mothballs right now, awaiting the outcome of the upcoming Chang'e-3 mission. If Chang'e-3 fails, we could see this backup lander launched within two years on an identical mission profile.

This analyst expects a happier outcome. The maturity of China's space technology suggests that this mission will be as successful as China's previous voyages to the Moon. It will take some time to complete the mission and then digest the copious amounts of data, both scientific and engineering, that the mission will return.

This will mean that the back-up lander will probably be grounded for a few years more. Although the spacecraft will complete the same basic mission objectives of landing on the Moon and deploying a rover, there will be changes. Planning a new mission for the spacecraft will be fun. China's engineers will have the luxury of using a proven system and the benefit of the scientific data it returns. We can expect that the next mission will be a little riskier.

The most significant change will be the landing site. China may wish to explore a region of the Moon that's geologically (ahem, selenologically) different from the first landing site. This could also involve landing in more difficult terrain, if the scientific returns are justified. Scouting areas that could help to select landing sites for Chinese lunar sample-return missions could be useful.

The instruments carried by the spacecraft could also be different. Some instruments will probably be flown again, although it is not clear if those supplied by international partners for the first mission will be repeated. This will provide opportunities for new experiments and new types of data.

Driving the rover on the Moon will be technically challenging. If China finds that the vehicle can handle its tasks, it may elect to give the next rover more autonomy or wider safety margins. This would improve its performance.

The lander and rover are heavy gear, requiring the use of the fairly powerful Long March 3B rocket. This analyst does not expect any changes in the launch vehicle or any increases in the spacecraft mass for the second landing mission.

The Chang'e-3 mission is China's first lunar landing spacecraft, but it will not be an isolated mission. More advanced Chinese lunar plans will be carried out in the decade ahead. The technology and landing systems demonstrated on this first landing will be critical to achieving these feats.

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.