We're getting closer to the launch of China's Tiangong 1 space laboratory. We've seen video footage and artwork of the exterior of this vehicle, but so far, information on Tiangong's interior has been scarce.

We don't know exactly what lies inside Tiangong, but we can take some educated guesses. Tiangong is a small spacecraft, and its interior fixtures allow little room for unnecessary items. This leads this author to reach one conclusion. There's probably no toilet on Tiangong.

Astronauts who visit the Tiangong 1 laboratory will travel aboard Shenzhou spacecraft, which are roughly the same size as the Tiangong module itself.

The Shenzhou spacecraft has enough room for three astronauts, along with all the equipment needed to keep them alive and functioning. Two Shenzhou spacecraft are expected to carry crews to Tiangong 1. These will be Shenzhous 9 and 10, expected to fly in 2012.

During an astronaut visit to Tiangong, the Shenzhou spacecraft will remain docked to the laboratory. The astronauts will also use this spacecraft for their return to Earth.

Shenzhou carries simple toilet facilities, as well as food preparation equipment and stores. These will all be within easy reach of the astronauts during their mission. Given this fact, it seems reasonable to assume that the toilet, as well as some of the food preparation gear, will not be replicated on Tiangong.

This will allow more space for experiments and other gear on board Tiangong itself. It also helps to solve a hygiene problem. Toilet and food preparation gear can be cleaned and emptied, but they still remain potential sources of odours and bacteria.

Leaving this type of gear on board the laboratory for an extended period could be messy for subsequent crews who visit the laboratory. If the toilet and kitchen are both replaced when each mission flies, then the gear should be kept relatively clean.

There's also another good reason for flying a fresh toilet with each crew. It minimizes the chance that the gear will break down. A broken toilet on board a cramped spacecraft would be a serious nuisance, as astronauts who have lived with the problem can attest.

Given the relatively small size of the Tiangong laboratory, it is probable that the astronauts will work inside it, but still spend much of their flight inside their own Shenzhou spacecraft.

This will not only allow them to use the facilities on board Shenzhou, but give them extra personal space. Shenzhou will offer more than a bathroom and kitchen. It will probably also serve as a bedroom.

Overall, the combined space aboard Shenzhou and Tiangong will not be large, but there will still be more personal space per crewmember than many other space missions. The astronauts themselves should also be fairly comfortable with the facilities and the food.

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