Space Suits - Definitions for the Clothing & Textile Industry

A space suit is a complex system of garments and equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space. This applies to extra-vehicular activity outside spacecraft orbiting Earth and has applied to walking, and riding the Lunar Rover, on the Moon.

Some of these requirements also apply to pressure suits worn by people such as high-altitude fighter pilots who may fly so high that breathing pure oxygen at surrounding pressure would not provide enough oxygen for them to function: see hypoxia.

Spacesuit requirements

Several things are needed for the spacesuit to function properly in space. It must provide:

• a stable internal pressure. This can be less than earth's atmosphere, as there is usually no need for the spacesuit to carry nitrogen.
• breathable oxygen. Usually a rebreather is used along with a supply of fresh oxygen.
• temperature regulation. Heat can only be lost in space by thermal radiation, or conduction with objects in physical contact with the space suit. Since heat is lost very slowly by radiation, a space suit almost always has only a cooling system and heavy insulation on the hands and possibly feet.
• electromagnetic radiation shielding.
• micrometeoroid protection.
• mobility.
• a communication system.
• means to recharge and discharge gases and liquids.
• a means to maneuver, dock, release, and tether on space craft.

Theories of spacesuit design

A space suit should allow its user natural and unencumbered movement. The only way this is possible is for the space suit to maintain a constant volume no matter what position the wearer is in. This is because mechanical work is needed to change the volume of a constant pressure system. If moving an arm or hand causes a change in the volume of the space suit, then the astronaut has to do extra work every time he bends that joint, and he has to maintain a force to keep the joint bent. Even if this force is very small, it can be seriouly fatiguing to constantly fight against your suit. It also makes delicate movements very difficult.

All space suit designs try to minimize or eliminate this problem. The most common solution is to form the suit out of multiple layers. The bladder layer is a rubbery, airtight layer much like a balloon. The restraint layer goes outside the bladder, and provides a specific shape for the suit. Since the bladder layer is larger than the restraint layer, the restraint takes all of the stresses caused by the pressure of the suit. Since the bladder is not under pressure, it will not "pop" like a balloon, even if punctured. The restraint layer is shaped in such a way that bending a joint will cause pockets of fabric, called gores, to open up on the outside of the joint. This makes up for the volume lost on the inside of the joint, and keeps the suit at a constant volume. However, once the gores are opened all the way, the joint cannot be bent anymore without a considerable amount of work.

In some Russian spacesuits strips of cloth were wrapped tightly round the spaceman's arms and legs outside the spacesuit to stop the spacesuit from ballooning when in space.

There are three theoretical approaches:

• Flexible pressure suits are the kind most in use. They combine all the bad features: heavy weight, the need for a cool suit, and difficult motion because the suit wants to blow up like a balloon. Their one saving grace is that they do not limit the range of motion.
• Hard-shell suits are usually made of metal or composite materials. While they resemble suits of armor, they are also designed to maintain a constant volume. However they tend to be difficult to move, as they rely on bearings instead of bellows over the joins, and often end up in odd positions that must be manipulated to regain mobility.
• Mixed suits have hard-shell parts and fabric parts. NASA's Extravehicular Mobility Unit  uses a hard-shell torso and fabric limbs.
• Skintight suits, or mechanical counterpressure suits, use a heavy elastic body stocking to compress the body. The head is encompassed in a pressurized helmet, but the rest of the body is pressurized only by the elastic effect of the suit. This eliminates the constant volume problem, and reduces the possibility of a space suit depressurization. However, these suits are very difficult to put on and face problems with providing a constant pressure everywhere. Most proposals use the body's natural sweat to keep cool. See space activity suit for more information.

One inconvenience with some spacesuits is the head being fixed facing forwards and being unable to turn to look sideways: astronauts call this effect "alligator head".