Three astronauts will soon board China's Tiangong 1 space laboratory after the Shenzhou 9 spacecraft docks with it. The first Chinese crew to fly in space in roughly four years includes China's first woman in space. This will also be the first crew to occupy a Chinese space laboratory.

The astronauts will find themselves very busy aboard the laboratory, with tests, tasks and experiments to perform. One astronaut will also remain on board the Shenzhou 9 spacecraft, ready to evacuate the crew in the event of an emergency.

Right now, it isn't clear who will stay on board Shenzhou, or if this role will be rotated between different crew members. It also isn't clear how the astronauts will alternate between work and sleep. Managing a three-person crew occupying two different spacecraft poses challenges to time management, but it also presents some opportunities.

Even if the crew rotate between duties on board Tiangong and Shenzhou, it's likely that there will always be at least one astronaut awake and on duty somewhere on either of the two spacecraft. This will allow work to be performed and systems to be monitored continuously.

It also seems probable that the two astronauts on board Tiangong 1 will both use the same work/sleep routines. This is partially due to the potential nuisance of trying to sleep on board an operational spacecraft, but this is not a serious problem.

Tiangong features two private sleeping bays, similar to those used on other space stations. This would presumably give astronauts a great deal of privacy and isolation from the rest of the cabin.

The main purpose of keeping both astronauts awake at the same time on Tiangong would be experimental. It is expected that much of the work done on board the laboratory will involve physiological studies of the astronauts themselves.

For much of this work, one astronaut will probably administer tests while the other astronaut receives them. Other experiments could also work better with a second crewmember to keep watch, and possibly help to contain spills in the small cabin.

While the astronauts on board Tiangong are at work, it's possible that the third crewmember on board Shenzhou will be sleeping for at least part of the time. This would be easy to do. The astronaut would be in an entirely separate spacecraft, and fairly isolated from the work going on inside the laboratory.

The third astronaut will probably sleep inside the spacecraft's bell-shaped descent module, which is the segment of the spacecraft used for the re-entry and landing. This module is separated from Tiangong by the fairly large Shenzhou Orbital Module at its front, which provides even more peace.

Scheduling pleasant sleep schedules is more than just important for keeping a constant vigil on the mission. It's also probably critical to some of the medical tests. It seems possible that physiological responses to sleep will be monitored, and interrupting sleep would disrupt these measurements.

Although there could be some shifting of duties, it seems unlikely that everyone will rotate between all roles. This analyst does not believe that China's first female astronaut will be placed alone on "Shenzhou duty", ready to activate the spacecraft in the event of an emergency. China's two women astronauts

have been judged fit for the mission, but were given an accelerated training program to prepare them for spaceflight fairly quickly. Commanding and controlling a Shenzhou spacecraft, especially in a critical time, would presumably require an astronaut with more training.

We shall see what happens after the astronauts of Shenzhou 9 begin their work.

Dr Morris Jones is an Australian space analyst and writer. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries.