a better focus on shenzhou

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DRAGON SPACE A Better Focus On Shenzhou

Spacewalking astronauts must purge their bodies of nitrogen beforethey 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 wewere seeing. In my previous article, "Two Suits for Shenzhou", I explained

that while some details were clearer, China needed to say more about thebasic mission plan.

Now, we have apparently confirmed some basic details of the spacewalkplanned 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 inspace suits to prepare for extravehicular activities, and one astronautwill conduct a spacewalk and scientific experiments."

The nature of the spacewalk is now clear. Shenzhou 7 will launch with acrew of three astronauts. Shortly before the spacewalk, two of these menwill enter the Orbital Module at the front of the spacecraft. The hatchlinking the Orbital Module to the Descent Module, containing the thirdastronaut, 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 suitsbefore they don them. Next, there will be more checks once the astronautsare inside their suits.

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

The aforementioned plans seemed fairly clear from previous Chinesestatements, but it's nice to see precise confirmation from officialsources.

Now that we have resolved the overall nature of the spacewalk, it's worth

considering some of the deeper technical issues. Spacewalking astronautsmust purge their bodies of nitrogen before they leave their spacecraft.

This is done by pre-breathing pure oxygen, or reducing the overall cabin


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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 toShenzhou'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 thespacesuit. 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 reportedsub-satellite to be carried on the mission, which would seem to be aremote camera designed to photograph the historic spacewalk. Hopefully, it

will still be carried.

Finally, we should ponder the activities of the second astronaut in theOrbital Module, who will be exposed to the vacuum of space, but will notactually leave the interior of the spacecraft.

His role will presumably be to monitor and possibly help his colleague inthe 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 morrisjonesNOSPAMhjotmail.com. ReplaceNOSPAM with @ to send email.

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