China has again confirmed the widely reported statement that Shenzhou 7 is to feature a spacewalk. This is a logical follow-on to China's previous missions of placing an astronaut into orbit, then demonstrating the capability of supporting more than one astronaut on an extended mission. China has again indicated that the mission will fly in 2007, in keeping with China's consistent but slow pacing of flights.

China has offered little clues about its systems for spacewalking. The in-flight pressure suits worn by Shenzhou astronauts have been extensively documented and exhibited. The similarities to the Sokol spacesuits worn by Russian Soyuz crewmembers are striking. China is known to have derived much inspiration from the Russian space program, so it's reasonably to suspect that their extravehicular spacesuits have been influenced by Russia's Orlan suits. Modifications could be made to allow the suit to pass through the hatch in Shenzhou's Orbital Module.

But China could still be blazing a new trail, as far as comparisons to Soyuz are concerned. Extravehicular activities performed directly from Russian Soyuz spacecraft are rare, and none have been attempted using a modern Orlan suit. In 1968, Soyuz 4 and 5 docked in orbit. Two crewmembers spacewalked from one Soyuz to the other.

The small Soyuz orbital modules on both vehicles were used as airlocks, while the non-spacewalking crewmembers remained inside the pressurized descent modules of both spacecraft. The suits used on this occasion were not really comparable to current Russian EVA systems. Since then, every Russian EVA has involved the use of a space station. Russia never carried out EVA from a Soyuz vehicle flying unattached to anything else.

It's likely that the Shenzhou EVA protocol calls for a spacewalking astronaut to enter the Orbital Module and don the EVA suit, which will be stored in this module for launch. Due to space limitations, there will probably be only a single EVA suit on the flight. A second crewmember will probably help him dress for vacuum, inspect the suit and carry out safety checks. Then the support astronaut will return to the Descent Module and seal the hatch to the Orbital Module.

The EVA astronaut will depressurize the Orbital Module and open the large cylindrical hatch used to enter the spacecraft. He should be tethered to Shenzhou by a leash which will prevent him from floating away, but will probably not carry power or consumables. These will be provided by a backpack, or possibly by a distributed system of tanks and pouches on his thighs.

The spacewalking astronaut will climb outside of Shenzhou using handrails attached to the exterior of the Orbital Module. Cameras pointing through the hatch of the orbital module, and probably outside the module, will record this historic moment. An astronaut inside the Descent Module will also be pointing cameras through the window. There will be obligatory speeches by the astronauts and carefully coordinated responses by officials at Mission Control. The performance of the spacesuit and the health of the spacewalking astronaut will be checked. Then, if everything has gone well, the EVA will probably move onto another phase.

One of the main goals of EVA is to inspect, repair or retrieve components outside a spacecraft. So the first Shenzhou spacewalker will soon be at work. He will probably photograph the exterior of the spacecraft using a hand-held camera. Next, a small sample package, placed on the exterior of the Orbital Module, will probably be retrieved. This could contain seeds, aerospace materials, or even the elusive pig spermatozoa experiment which apparently vanished from Shenzhou 6.

The EVA will probably be kept short, possibly for a total duration of half an hour. The astronaut's movements will probably be restricted to areas where he can be monitored constantly by his crewmates, and by television cameras. He will probably not be permitted to touch or approach the Descent Module, or sensitive areas such as the solar panels.

Afterwards, China's first spacewalker will return to the Orbital Module, close the hatch and repressurize the module. He will soon be joined by his colleague from the Descent Module, who will probably perform rudimentary medical checks on him. And Shenzhou will have reached another milestone.

Previous reports have hinted that Shenzhou 7 could carry three astronauts. China's latest statements say nothing about crew size, but the earlier reports seem logical. Shenzhou has been designed to accommodate a crew of three. Having launched one astronaut, then two, a full crew load would be the next obvious step. It would also allow Shenzhou 7 to accomplish the other major task for a "solo" Shenzhou flight: maximum crew size.

China will want to demonstrate that it can support a crew of three, but it may also be considering if this is really ideal for future missions. Russian Soyuz, Salyut and Soyuz-dependent ISS crews have sometimes been launched with three crewmembers, but have generally settled on a standard crew complement of two. This, according to Russian mission planners, seemed to offer the most optimal use of resources. China may eventually reach the same conclusions.

The duration of Shenzhou 7 will probably be similar to that of Shenzhou 6. A flight of four or five days would offer enough time for mission goals to be satisfied, but not stretch logistics too far. Given the added complications of another crewmember and the EVA, a slightly shorter mission could be favoured.

China has also given more clues about missions beyond Shenzhou 7, which essentially represents the start of China's space station program. More discussion of this will follow in another article.

Dr Morris Jones is a lecturer at Deakin University, Australia

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