Space suit

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.

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 space suit worn by a human in space was the Soviet Union SK-1 series.

Spacesuit requirements

A 3D anaglyph of a space suit. 3D red cyan glasses are recommended to view this image correctly.

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)

As part of astronautical hygiene control (i.e., protecting astronauts from extremes of temperature, radiation, etc.), a spacesuit is essential for extravehicular activity. Within its 18,000 or so parts, it contains everything an astronaut needs to stay alive, including oxygen, water, temperature control, and carbon dioxide removal. Because of the hazards from micro-meteoroids traveling at 27,000 kilometers per hour, it is important that the outer layer of the suit be puncture-resistant. The Apollo/Skylab A7L suit included eleven layers in all: an inner liner, a liquid cooling and ventilation garment, a pressure bladder, a restraint layer, another liner, and a thermal micrometeoroid garment consisting of five aluminized insulation layers and an external layer of white Ortho-Fabric. This spacesuit is capable of protecting the astronaut from temperatures ranging from -156 °C to +121 °C.

It is expected that manned exploration of the Moon and Mars will occur within the next two decades. During exploration, there will be the potential for lunar/Martian dust to be retained on the spacesuit. When the spacesuit is removed on return to the spacecraft, there will be the potential for the dust to contaminate surfaces and increase the risks of inhalation and skin exposure. Astronautical hygienists are testing materials with reduced dust retention times and the potential to control the dust exposure risks during planetary exploration. Novel ingress/egress approaches, such as suitports, are being explored as well.

In NASA spacesuits, communications are provided via a cap worn over the head, which includes earphones and a microphone. Due to the coloration of the version used for Apollo and Skylab, which resembled the coloration of the comic strip character Snoopy, these caps became known as "Snoopy 

caps".

Operating pressure

Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about 32.4 kPa (240 Torr; 4.7 psi), equal to the 20.7 kPa (160 Torr; 3.0 psi) partial pressure of oxygen in the Earth's atmosphere at sea level, plus 5.3 kPa (40 Torr; 0.77 psi) CO2 and 6.3 kPa (47 Torr; 0.91 psi) water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the alveolar gas equation.[1] The latter two figures add to 11.6 kPa (87 Torr, 1.7 psi), which is why many modern spacesuits do not use 20.7 kPa (160 Torr; 3.0 psi), but 32.4 kPa (240 Torr; 4.7 psi) (this is a slight overcorrection, as alveolar partial pressures at sea level are slightly less than the former). In spacesuits that use 20.7 kPa, the astronaut gets only 20.7 kPa − 11.7 kPa = 9.0 kPa (68 Torr; 1.3 psi) of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of 1,860 m (6,100 ft) above sea level. This is about 78% of normal sea level pressure, about the same as pressure in a commercial passenger jet aircraft, and is the realistic lower limit for safe ordinary space suit pressurization which allows reasonable capacity for work.

When space suits below a specific operating pressure are used from craft that are pressurized to normal atmospheric pressure (such as the space shuttle), this requires astronauts to "pre-breathe" (meaning pre-breathe pure oxygen for a period) before donning their suits and depressurizing in the air lock. This procedure purges the body of dissolved nitrogen, so as to avoid decompression sickness ("the bends") due to overrapid depressurization from a nitrogen-containing atmosphere.

Exposure to space without a spacesuit

The human body can briefly survive the hard vacuum of space unprotected, despite contrary depictions in some 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.

Theories of spacesuit design

A space suit should allow its user natural unencumbered movement. Nearly all designs try to maintain a constant volume no matter what movements the wearer makes. This is because mechanical work is needed to change the volume of a constant pressure system. If flexing a joint reduces the volume of the spacesuit, then the astronaut must 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 seriously fatiguing to constantly fight against one's suit. It also makes delicate movements very difficult. The work required to bend a joint is dictated by the formula

where Vi and Vf are respectively the initial and final volume of the joint, P is the pressure in the suit, and W is the resultant work. It is generally true that all suits are more mobile at lower pressures. However, because a minimum internal pressure is dictated by life support requirements, the only means of further reducing work is to minimize the change in volume.

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 inside 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 causes pockets of fabric, called "gores", to open up on the outside of the joint, while folds called "convolutes" fold up on the inside of the joint. The gores make up for the volume lost on the inside of the joint, and keep the suit at a nearly constant volume. However, once the gores are opened all the way, the joint cannot be bent any further without a considerable amount of work.

In some Russian space suits, strips of cloth were wrapped tightly around the cosmonaut's arms and legs outside the spacesuit to stop the spacesuit from ballooning when in space.

The outermost layer of a space suit, the Thermal Micrometeoroid Garment, provides thermal insulation, protection from micrometeoroids, and shielding from harmful solar radiation.