A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extravehicular activity (EVA), work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the Moon, and en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, and to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained oxygen supply and environmental control system is frequently employed to allow complete freedom of movement, independent of the spacecraft.
Three types of space suits exist for different purposes: IVA (intravehicular activity), EVA (extravehicular activity), and IEVA (intra/extravehicular activity). IVA suits are meant to be worn inside a pressurized spacecraft, and are therefore lighter and more comfortable. IEVA suits are meant for use inside and outside the spacecraft, such as the Gemini G4C suit. They include more protection from the harsh conditions of space, such as protection from micrometeoroids and extreme temperature change. EVA suits, such as the EMU, are used outside spacecraft, for either planetary exploration or spacewalks. They must protect the wearer against all conditions of space, as well as provide mobility and functionality.[1]
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Some of these requirements also apply to pressure suits worn for other specialized tasks, such as high-altitude reconnaissance flight. At altitudes above the Armstrong limit, around 19,000 m (62,000 ft), water boils at body temperature and pressurized suits are needed.
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 SK-1 suit worn by Yuri Gagarin in 1961.
Advanced suits better regulate the astronaut's temperature with a Liquid Cooling and Ventilation Garment (LCVG) in contact with the astronaut's skin, from which the heat is dumped into space through an external radiator in the PLSS.
During exploration of the Moon or Mars, there will be the potential for lunar or Martian dust to be retained on the space suit. When the space suit 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 and egress approaches, such as suitports, are being explored as well.
In NASA space suits, 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".
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 due to rapid depressurization from a nitrogen-containing atmosphere.[1]
In the US space shuttle, cabin pressure was reduced from normal atmospheric to 70kPa (equivalent to an altitude of about 3000m) for 24 hours before EVA, and after donning the suit, a pre-breathing period of 45 minutes on pure oxygen before decompressing to the EMU working pressure of 30kPa. In the ISS there is no cabin pressure reduction, instead a 4 hour oxygen pre-breathe at normal cabin pressure is used to desaturate nitrogen to an acceptable level. US studies show that a rapid decompression from 101kPa to 55kPa has an acceptable risk, and Russian studies show that direct decompression from 101kPa to 40kPa after 30 minutes of oxygen pre-breathing, roughly the time required for pre-EVA suit checks, is acceptable.[1]
The human body can briefly survive the hard vacuum of space unprotected,[3] despite contrary depictions in some popular science fiction. 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, but human flesh expands up to about twice its volume due to ebullism in such conditions, giving the visual effect of a body builder rather than an overfilled balloon.[4]
In space, there are highly energized subatomic particles that can cause radiation damage by disrupting essential biological processes. Exposure to radiation can create problems via two methods: the particles can react with water in the human body to produce free radicals that break DNA molecules apart, or by directly breaking the DNA molecules.[1][5]
The vacuum environment of space has no pressure, so gases will expand and exposed liquids may evaporate. Some solids may sublimate. It is necessary to wear a suit that provides sufficient internal body pressure in space.[1][6] The most immediate hazard is in attempting to hold one's breath during explosive decompression as the expansion of gas can damage the lungs by overexpansion rupture. These effects have been confirmed through various accidents (including in very-high-altitude conditions, outer space and training vacuum chambers).[3][7] Human skin does not need to be protected from vacuum and is gas-tight by itself.[4] It only needs to be mechanically restrained to retain its normal shape and the internal tissues to retain their volume. This can be accomplished with a tight-fitting elastic body suit and a helmet for containing breathing gases, known as a space activity suit (SAS).[clarification needed][citation needed]
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 space suit, then the astronaut must do extra work every time they bend that joint, and they have 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 space suit to stop the space suit from ballooning when in space.[citation needed]
Soft suits typically are made mostly of fabrics. All soft suits have some hard parts; some even have hard joint bearings. Intra-vehicular activity and early EVA suits were soft suits.[citation needed]
Hard-shell suits are usually made of metal or composite materials and do not use fabric for joints. Hard suits joints use ball bearings and wedge-ring segments similar to an adjustable elbow of a stove pipe to allow a wide range of movement with the arms and legs. The joints maintain a constant volume of air internally and do not have any counter-force. Therefore, the astronaut does not need to exert to hold the suit in any position. Hard suits can also operate at higher pressures which would eliminate the need for an astronaut to pre-breathe oxygen to use a 34 kPa (4.9 psi) space suit before an EVA from a 101 kPa (14.6 psi) spacecraft cabin. The joints may get into a restricted or locked position requiring the astronaut to manipulate or program the joint.[clarification needed] The NASA Ames Research Center experimental AX-5 hard-shell space suit had a flexibility rating of 95%. The wearer could move into 95% of the positions they could without the suit on.[citation needed]
Hybrid suits have hard-shell parts and fabric parts. NASA's Extravehicular Mobility Unit (EMU) uses a fiberglass Hard Upper Torso (HUT) and fabric limbs.[citation needed] ILC Dover's I-Suit replaces the HUT 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.[citation needed] Virtually all workable space suit 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. 152ee80cbc
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