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1 Spacesuit requirements

In order to function properly in the environment of space, there are several requirements which must be fulfilled to achieve proper system operation. A suit must provide:

• internal pressure stabilization (like the air pressure on Earth),
• breathing gas storage
• breathable gas mixture regulation (to balance oxygen and nitrogen, etc,.. for conditions)
• Exhaled gas storage or recycling
• temperature regulation, specifically cooling: While space is very cold, there's nowhere for the heat from the astronaut to go; also, the astronaut will likely be warmed by sunlight.
• radiation shielding.
• appropriate wear surfaces for use (shoes, knee pads, etc.)
• appropriate mount interfaces for loading and unloading gases and liquids.
• appropriate system mounts for maneuvering with space craft, through environmental locks, docking, releasing, tethering to system modules.

2 Theories of spacesuit design

Added to these requirements, each technically solvable, is the requirement for the spacesuit to be movable, and allow the user some degree of freedom of motion. This is actually one of the most difficult parts of spacesuit design.

Think of an movable part of the suit, for instance, an arm, when the arm is bent from an original position straight out. The arm is inside a gas-filled tube, largely identical in dynamics to the long balloons use to make balloon animals for children. If you attempt this same manuver with such a balloon you'll find it is actually difficult: the balloon will fold at some point along its length, which forces air out of the fold into the rest of the balloon, increasing pressure. If you release the force, the balloon, or spacesuit, will return to its original unbent state.

This constant action against the user's motion can be seriously fatiguing, and make delicate control almost impossible. Current solutions focus on using bellows-like folds, the folds grow larger on the outside of the bend while the inside grows smaller, equalizing pressure. However these have a limited amount of motion, once the outside folds are all the way open, they cannot move any further. Such a system can be seen in the Apollo suit in the picture above, the diamond shapes in the fabric over the right elbow are caused by the bellows under it.

The goal of spacesuit design, then, is to provide all the needed requirements in a suit that is also highly mobile. Today's suit designs fail in this goal, although they are improving. More "radical" design concepts have been proposed.

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 have constant volumeVolume (also called capacity is a quantification of how much space an object occupies. The SI unit for volume is the cubic metre (American spelling meter). The volume of a solid object is a numerical value given to describe the three-dimensional concept os, and motion is therefore very easy, because the pressure inside the suit does not oppose motion. Instead of air conditioningNote: in the broadest sense, "air conditioning" can refer to any form of " heating, ventilation, and air-conditioning. This article is specifically about the use of refrigeration for this purpose. The first album of the pop group Curved Air was Airconditi, most hard suits use a cool-suit with soft tubes carrying water, which is then evaporated into the vacuum for cooling. 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 in order to regain mobility.
• Skintight suits use a heavy body stocking to compress the body, as opposed to pressurizing it with air. Most proposals use the body's natural sweat to keep cool. See space activity suitA space activity suit is a kind of spacesuit, which provides mechanical pressure by means of elastic garments as opposed to pressurizing the suit with the breathing gas, as is standard practice in regular suits. History Original research was done by Paul for more information.