A space suit is a complex system of garments, 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 (EVA) outside spacecraft orbiting Earth and has applied to walking, and riding the Lunar Rover, on the Moon.
A G-suit is worn by aviators and astronauts who are subject to high levels of acceleration ('G'). It is designed to prevent a black-out and g-LOC (g-induced Loss Of Consciousness), due to the blood pooling in the lower part of the body when under G, thus depriving the brain of blood.
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Some of these requirements also apply to pressure suits worn for other specialized tasks, such as high-altitude reconnaissance flight. Above Armstrong's Line (around 19,000 m/62,000 ft), the atmosphere is so thin that pressurized suits are needed. Hazmat suits that superficially resemble space suits are sometimes used when dealing with biological hazards.
The first full pressure-suits for use at extreme altitudes were designed by individual inventors as early as the 1930s. The first commercial space suits were made by the Goodrich Corporation.
The human body can briefly survive the hard vacuum of space unprotected, despite contrary depictions in much popular science fiction. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. No snap freeze effect occurs because all heat must be lost through thermal radiation or the evaporation of liquids, and the blood does not boil because it remains pressurized within the body. The greatest danger is in attempting to hold one's breath before exposure, as the subsequent explosive decompression can damage the lungs. These effects have been confirmed through various accidents (including in very high altitude conditions, outer space and training vacuum chambers). Human skin does not need to be protected from vacuum and is gas-tight by itself. Instead it only needs to be mechanically compressed to retain its normal shape. This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a Space activity suit.
A space suit must perform several functions to allow its occupant to work safely and comfortably. 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 (which comprises about 78% of earth's atmosphere and is not used by the body). Lower pressure allows for greater mobility, but requires the suit occupant to breathe pure oxygen for a time before going into this lower pressure, to avoid decompression sickness.
- Mobility. Movement is typically opposed by the pressure of the suit; mobility is achieved by careful joint design. See the Theories of spacesuit design section.
- Breathable oxygen. Circulation of cooled and purified oxygen is controlled by the Primary Life Support System.
- Temperature regulation. Unlike on Earth, where heat can be transferred by convection to the atmosphere, in space heat can be lost only by thermal radiation or by conduction to objects in physical contact with the space suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and the temperature inside the suit is regulated by a Liquid Cooling Garment in contact with the astronaut's skin, as well as air temperature maintained by the Primary Life Support System.
- Shielding against ultraviolet radiation
- Limited shielding against particle radiation
- Protection against small micrometeoroids, provided by a Thermal Micrometeoroid Garment, which is the outermost layer of the suit
- A communication system
- Means to recharge and discharge gases and liquids
- Means to maneuver, dock, release, and/or tether onto spacecraft
- Means of collecting and containing solid and liquid waste (such as a Maximum Absorbency Garment)
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 joints, 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 fiberglass Hard Upper Torso (HUT) and fabric limbs. ILC Dover's I-Suit replaces the hard upper torso with a fabric soft upper torso to save weight, restricting the use of hard components to the joint bearings, helmet, waist seal, and rear entry hatch. Virtually all workable spacesuit designs incorporate hard components, particularly at interfaces such as the waist seal, bearings, and in the case of rear-entry suits, the back hatch, where all-soft alternatives are not viable.
Skintight suits, also known as mechanical counterpressure suits or space activity suits, are a proposed design which would use a heavy elastic body stocking to compress the body. The head is 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, reduces the possibility of a space suit depressurization and gives a very lightweight suit. 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.
A G-suit, or the more accurately named anti-G suit, is worn by aviators and astronauts who are subject to high levels of acceleration force ('Gs'). It is designed to prevent a black-out and G-LOC (G-induced Loss Of Consciousness), due to the blood pooling in the lower part of the body when under acceleration, thus depriving the brain of blood.
A G-suit does not so much increase the G-threshold, but makes it possible to sustain high G longer without excessive physical fatigue. The resting G-tolerance of a typical person is anywhere from 3-5 G's depending on the person. A G-suit will typically add 1 G of tolerance to that limit. Pilots still need to practice the 'G-straining maneuver' that consists of tensing the abdominal muscles in order to tighten blood vessels so as to reduce blood pooling in the lower body. High G is not comfortable, even with a G-suit. In older fighter aircraft, 6 Gs was considered a high level, but with modern fighters nine or more Gs can be sustained structurally making the pilot the critical factor in maintaining high maneuverability in close aerial combat.
A G-suit is a special garment and generally takes the form of tightly-fitting trousers, which fit either under or over (depending on the design) the flying suit worn by the aviator or astronaut. The trousers are fitted with inflatable bladders which, when pressurized through a G-sensitive valve in the aircraft or spacecraft, press firmly on the abdomen and legs, thus restricting the draining of blood away from the brain during periods of high acceleration. In addition, in some modern very high-G aircraft, the Anti-G suit effect is augmented by a small amount of pressure applied to the lungs (partial pressure breathing), which also enhances resistance to high G. The effects of Anti-G suits and partial pressure breathing are straightforward to replicate in a simulator, although the continuous G forces themselves can only be produced artificially in devices such as centrifuges.
If blood is allowed to pool in the lower areas of the body, the brain will be deprived of blood leading to temporary hypoxia. Hypoxia causes first a brownout (a dimming of the vision), also called grey-out, followed by tunnel-vision and ultimately complete loss of vision 'blackout' followed by G-induced Loss Of Consciousness or 'G-LOC'. The danger of G-LOC to aircraft pilots is magnified because on relaxation of G there is a period of disorientation before full sensation is re-gained. G-force induced hypoxia has resulted in a number of fatalities in which the aircraft and crew are lost.
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