In just a few months, China's Shenzhou 7 spacecraft will lift off on a mission to perform China's first spacewalk. The mission is exciting, but the media silence is deafening. We know almost nothing about the spacesuit, or how the astronaut will be connected to his spacecraft. Trying to work out what's happening behind closed doors requires a bit of deductive reasoning.

In my previous 2008 article("Breaking the Silence on Shenzhou"), I discussed what little is known about the spacesuit and the procedures for the spacewalk. But alongside the technical preparations for Shenzhou 7, there's a human element. We don't know who is going to fly on the mission, or how they are being selected.

China has announced that Shenzhou 7 will fly with a three-person crew. This is the maximum crew level for Shenzhou. With this fact, and some knowledge of previous training procedures for China's astronauts, we can speculate on how crews are being prepared for the mission.

China reportedly has an astronaut corps of 14 men, who were all selected in 1998. The group has apparently experienced no change in its makeup since then. The names, faces and some minor biographical details are known for most of these men. But generally, China keeps its astronauts under wraps, just like its spacecraft. But we know that these men represent the pool for potential Shenzhou 7 crews.

China formed several two-man teams to train for its previous Shenzhou 6 mission in 2005, which carried two astronauts. The teams trained in parallel, competing for the honour of carrying out the flight. A few months before the mission, some of the teams were apparently shortlisted for the final selection, and others were stood down.

Selection was allegedly based on the performance of the teams in simulations and training. The final prime crew for Shenzhou 6, consisting of Fei Junlong and Nie Haisheng, was reportedly selected just prior to the mission.

It seems reasonable to expect that China is following similar procedures for Shenzhou 7. Three-man teams are training in parallel, and one team will eventually be selected for the flight. But some simple arithmetic makes this practice interesting. You cannot neatly divide a pool of 14 people into teams of three people, without leaving two behind. How is China managing its astronauts?

The simplest strategy would be to assume that there are four separate teams of three astronauts, plus two leftovers. Who has been left out of the crews? China could have elected to sideline some of its already-flown astronauts, which includes the Shenzhou 6 crew and Yang Liwei, the sole astronaut on Shenzhou 5.

Then again, China could have placed one experienced astronaut on three of the teams, to serve as mission commanders. The sidelined astronauts could either be low-ranking performers, people who have fallen out of political favour, or the two astronaut candidates who trained in Russia as instructors.

But again, this is just speculation. We don't know who's in, who's out, or how the candidates are being managed. We also don't know for sure if anyone has left the astronaut corps, or has been unofficially sidelined. We will probably only know the final crew of Shenzhou 7 shortly before liftoff. It is unclear when the Chinese themselves will decide on the crew. But a full analysis of the selection procedures will probably not appear for a long time.

Dr Morris Jones is an Australian spaceflight analyst and writer. He has covered the Shenzhou program since 1999. Email morrisjonesNOSPAMhotmail.com Replace NOSPAM with @ to send email.