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A Better Focus On Shenzhou

Spacewalking astronauts must purge their bodies of nitrogen before they leave their spacecraft.
by Morris Jones
Sydney, Australia (SPX) Jun 25, 2008
Information on the upcoming Shenzhou 7 has been gradually improving in recent months. It's like watching a badly focused image gradually sharpen, while we looked at some imprecise details and wondered exactly what we were seeing. In my previous article, "Two Suits for Shenzhou", I explained that while some details were clearer, China needed to say more about the basic mission plan.

Now, we have apparently confirmed some basic details of the spacewalk planned for this mission.

A short June 20 report in People's Daily, China's state-run newspaper, states that "two astronauts will enter the spaceship orbital module in space suits to prepare for extravehicular activities, and one astronaut will conduct a spacewalk and scientific experiments."

The nature of the spacewalk is now clear. Shenzhou 7 will launch with a crew of three astronauts. Shortly before the spacewalk, two of these men will enter the Orbital Module at the front of the spacecraft. The hatch linking the Orbital Module to the Descent Module, containing the third astronaut, will be sealed soon after the crew splits in two.

The Orbital Module will house the EVA suits during the flight, and the two astronauts will spend a considerable amount of time checking the suits before they don them. Next, there will be more checks once the astronauts are inside their suits.

The air pressure inside the orbital module will be gradually reduced to vacuum, and the large circular outer hatch on the side of the Orbital Module will then be swung inwards. One astronaut will then carefully step outside the module, clutching handrails on the outside of the spacecraft, to become China's first spacewalker.

The aforementioned plans seemed fairly clear from previous Chinese statements, but it's nice to see precise confirmation from official sources.

Now that we have resolved the overall nature of the spacewalk, it's worth considering some of the deeper technical issues. Spacewalking astronauts must purge their bodies of nitrogen before they leave their spacecraft.

This is done by pre-breathing pure oxygen, or reducing the overall cabin pressure in the spacecraft. This prevents the onset of the "bends", familiar to sea divers as decompression sickness, when they are exposed to space in the reduced pressure environment of their spacesuit.

How will the Shenzhou spacewalkers pre-breathe? Will the entire spacecraft be subjected to reduced atmospheric pressure, or will there be a pre-breathe session inside the sealed Orbital Module? References to Shenzhou's cabin environment suggest that, under normal flight conditions, the pressure and oxygen balance is fairly similar to Earth's atmosphere. Clearly, something will have to be done to allow the spacewalkers to adapt.

We have been given another vague reference to "experiments" to be conducted by the spacewalker, but nothing specific.

Presumably, much of the work conducted by the spacewalker would be tests of the spacewalker's ability to move and manipulate objects inside the spacesuit. Other activities could be planned, but we just don't know yet. One option would be to retrieve exposed material samples from outside the spacecraft, and return them to Earth.

The latest article makes no reference to the previously reported sub-satellite to be carried on the mission, which would seem to be a remote camera designed to photograph the historic spacewalk. Hopefully, it will still be carried.

Finally, we should ponder the activities of the second astronaut in the Orbital Module, who will be exposed to the vacuum of space, but will not actually leave the interior of the spacecraft.

His role will presumably be to monitor and possibly help his colleague in the event of an emergency, but he could also end up as a camera jockey for the event. This astronaut will probably open and close the hatch, as well as handle the pressurization of the module.

The mission still seems to be on schedule for October this year. Bring it on!

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

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