Most of the mysteries surrounding the Shenzhou 7 mission have now been solved through media disclosures and some deductive reasoning on the part of analysts. But there's one outstanding mystery. We don't know exactly what is sitting on top of the Orbital Module of the Shenzhou 7 spacecraft.

Photography and diagrams of this part of the spaceship have been rare. When they have appeared, they have usually been vague.

The best photography of the spacecraft reveals a cluster of four small spheres, surrounding a slightly rectangular box.

What exactly is this? The gear placed at the front of the Shenzhou spacecraft has changed on different missions. Sometimes, it's been obvious to see what is was. Antennas look like antennas, and a camera box looks like a camera.

This one is less clear. It seems probable that the spheres are gas tanks. But what do they hold? This could be extra air for Shenhzhou's cabin. When the spacewalk is conducted, all of the air in the spacecraft's orbital module will be vented into space. This will need replenishing. These tanks could supplement the spacecraft's regular atmosphere reserves.

Alternatively, this could be air for the spacewalker. We still don't fully know if the spacewalker will use an internal air supply or a feed from an umbilical.

The box could be control equipment for regulating the gas from the tanks. I once thought that this could be the small satellite camera that will photograph the spacewalk. But recent Chinese statements seem to indicate that this satellite will be hand-launched by the astronauts themselves.

The satellite will probably be stored inside the spacecraft, and thrown out the hatch. The box, in any case, does not seem to resemble a free-flying spacecraft.

The general lack of any remote sensing equipment on the orbital module is understandable. Unlike previous missions, the Orbital Module of Shenzhou 7 will not be flying an extended mission after the main spacecraft returns to Earth.

Dr Morris Jones is an Australian spaceflight analyst. He is the author of "The Adventure of Mars" and "When Men Walked on the Moon". Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will accept media inquiries.