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Last Updated: Friday, 26 October 2007, 14:45 GMT 15:45 UK
Factfile: Walking in space
When astronauts step through an airlock on the Space Shuttle or the International Space Station into the harsh void of space, they are wearing a state-of-the-art EMU - or Extravehicular Mobility Unit.

QUICK FACTS
Cost per suit: $12m
Mass: 140kg
Manufacturers: Hamilton Sundstrand/ILC Dover
Spacesuits are designed to protect the human body from the extreme conditions of space, where temperatures can range from about 135 Celsius in direct sunlight to minus 82 Celsius in areas of shadow.

The spacesuit must be pressurised to protect against the near-vacuum of space, and sufficiently tough to withstand impacts from potentially lethal micrometeoroids and other orbiting debris.

Space suit graphic (BBC)

A fully fitted spacesuit consists of 13 layers of material nearly 9cm thick. Some key elements of the suit are:

Liquid Cooling and Ventilation Garment [LCVG]: Spacewalking is often strenuous work, so regulating body temperature is important. The LCVG is a double-layered bodysuit containing a network of fine, water-carrying tubes. This water is pumped around the garment to remove excess heat.

Pressure Garment: This double-layered garment maintains pressure at slightly below normal atmospheric levels. Without it, body fluids would boil under the intense force produced by exposure to the zero-pressure conditions found in the near-vacuum of space.

See a spacesuit up close

Thermal Micrometeoroid Garment [TMG]: Eight layers thick. Some consist of toughened substances such as Kevlar and protect against tiny pieces of space rock travelling at high speed.

Other layers of durable, breathable materials insulate the suit from extreme temperatures.

The outer layer is made of white ortho-fabric, which helps reflect radiation. Spacesuits only offer minimal protection from radiation however, so spacewalks can only take place during periods of low solar activity.

Maximum Absorbency Garment [MAG]: Because spacewalks usually last several hours, the MAG is worn underneath the LCVG to absorb and hold urine and faeces hygienically.

Hard Upper Torso [HUT]: This is a toughened fibreglass shell to which the various "limbs" of the suit are attached, as well as the helmet assembly. It also has mountings for various instrument units and at the back - most importantly - the Life Support System.

The HUT also has a holder for a rice-paper-wrapped cereal bar that astronauts can bite into in case of hunger. To avoid floating crumbs though, the whole bar must be eaten at once.

Space suit graphic (BBC)
Life Support System [LSS]: Worn as a "backpack", the LSS stores and regulates the oxygen supply and removes carbon dioxide breathed out via the Contaminant Control Cartridge.

The LSS holds enough oxygen to last for about seven hours. Prior to walking in space, astronauts must "pre-breathe" pure oxygen to remove nitrogen from the blood and prevent painful decompression sickness.

Another function is to pump cooling water around the suit and remove heat generated from both the astronaut's body and the spacesuit's various electrical systems.

In-suit drink bag: Spacewalking can be thirsty work, so astronauts are provided with a 900cl water bag which is attached by Velcro to the inside of the helmet. A special valve system prevents droplets of water from escaping and floating around the helmet.

Helmet Assembly and Extravehicular Visor Assembly: The helmet assembly is a transparent poly-carbonate shell attached to the hardened upper torso. It is designed to give a very clear field of vision; the inside faceplate is also sprayed with an anti-misting agent.

The visor assembly is impact-toughened and designed to reflect heat and light. The visor itself functions a little like a two-way mirror; externally tinted to restrict incoming solar glare, but allowing the astronaut a clear view from inside.

Powerful lamps are fitted to the top of the helmet to enable astronauts to see into areas of shadow. These also act as a light source for the helmet-mounted TV camera which relays images back to the space shuttle's flightdeck and mission control.

Space suit graphic (Nasa)





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