Editing Space suit (section)

== Requirements ==
[[File:STS-116 spacewalk 1.jpg|thumb|Space suits being used to work on the International Space Station.]]

A space suit must perform several functions to allow its occupant to work safely and comfortably, inside or outside a spacecraft. It must provide:
* A stable internal pressure. This can be less than Earth's atmosphere, as there is usually no need for the space suit 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 ''[[#Design concepts|Design concepts]]'' section.
* Supply of breathable oxygen and elimination of [[carbon dioxide]]; these gases are exchanged with the spacecraft or a [[Primary Life Support System|Portable Life Support System]] (PLSS)
* 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 [[heat conduction|conduction]] to objects in physical contact with the exterior of the suit. Since the temperature on the outside of the suit varies greatly between sunlight and shadow, the suit is heavily insulated, and air temperature is maintained at a comfortable level.
* A communication system, with external electrical connection to the spacecraft or PLSS
* [[File:AstroRad NASA.jpg|thumb|235x235px|AstroRad developed by Israeli StemRad anti Radiation spacesuit]]Means of collecting and containing solid and liquid bodily waste (such as a [[Maximum Absorbency Garment]])

=== Secondary requirements ===
[[File:First Six Women Astronauts with Rescue Ball - GPN-2002-000207.jpg|thumb|From left to right, Margaret R. (Rhea) Seddon, Kathryn D. Sullivan, Judith A. Resnick, Sally K. Ride, Anna L. Fisher, and Shannon W. Lucid{{mdash}}The first six female astronauts of the United States stand with a [[Personal Rescue Enclosure]], a spherical life support ball for emergency transfer of people in space]]
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.

Additional requirements for EVA include:
* Shielding against [[ultraviolet]] radiation
* Limited shielding against [[particle radiation]]
* Means to maneuver, dock, release, and tether onto a spacecraft
* Protection against small [[micrometeoroid]]s, some traveling at up to 27,000 kilometers per hour, provided by a puncture-resistant [[Thermal Micrometeoroid Garment]], which is the outermost layer of the suit. Experience has shown the greatest chance of exposure occurs near the [[gravitational field]] of a moon or planet, so these were first employed on the [[Apollo program|Apollo]] lunar EVA suits (see ''[[#United States suit models|United States suit models]]'' below).

[[File:Thermal Micrometeoroid Garment.gif|thumb|Layers of a space suit.]]

As part of [[astronautical hygiene]] control (i.e., protecting astronauts from extremes of temperature, radiation, etc.), a space suit is essential for extravehicular activity. The [[Apollo/Skylab A7L]] suit included eleven layers in all: an inner liner, a LCVG, 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 space suit is capable of protecting the astronaut from temperatures ranging from {{convert|-156|°C}} to {{convert|121|°C}}.{{Citation needed|date=December 2010}}

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 [[suitport]]s, 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 cap]]s".

=== Operating pressure ===
[[File:Prebreathe.jpg|thumb|Astronaut [[Steve MacLean (astronaut)|Steven G. MacLean]] pre-breathes prior to an EVA]]
Generally, to supply enough oxygen for [[Respiratory system|respiration]], a space suit using pure oxygen must have a pressure of about {{convert|32.4|kPa|Torr psi|sigfig=2|abbr=on}}, equal to the {{convert|20.7|kPa|Torr psi|sigfig=2|abbr=on}} [[partial pressure]] of oxygen in the [[Earth's atmosphere]] at sea level, plus {{convert|5.3|kPa|Torr psi|sigfig=2|abbr=on}} {{CO2}}{{citation needed|date=May 2020}} and {{convert|6.3|kPa|Torr psi|sigfig=2|abbr=on|lk=on}} [[water vapor]] pressure, both of which must be subtracted from the [[Pulmonary gas pressures|alveolar pressure]] to get alveolar oxygen partial pressure in 100% oxygen atmospheres, by the [[alveolar gas equation]].<ref>{{cite web |url=http://www.globalrph.com/martin_4_most2.htm |title=The Four Most Important Equations In Clinical Practice |last=Martin |first=Lawrence |website=GlobalRPh |publisher=David McAuley |access-date=June 19, 2013}}</ref> The latter two figures add to {{convert|11.6|kPa|Torr psi|sigfig=2|abbr=on}}, which is why many modern space suits do not use {{convert|20.7|kPa|Torr psi|sigfig=2|abbr=on}}, but {{convert|32.4|kPa|Torr psi|sigfig=2|abbr=on}} (this is a slight overcorrection, as alveolar partial pressures at sea level are slightly less than the former). In space suits that use 20.7&nbsp;kPa, the astronaut gets only 20.7&nbsp;kPa − 11.6&nbsp;kPa = {{convert|9.1|kPa|Torr psi|sigfig=2|abbr=on}} of oxygen, which is about the alveolar oxygen partial pressure attained at an altitude of {{convert|1860|m|ft|abbr=on}} above sea level. This is about 42% of normal partial pressure of oxygen at sea level, about the same as [[Cabin pressurization#Aircraft|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.

====Oxygen prebreathing====
{{see also|Decompression practice#Oxygen prebreathing}}
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.<ref name="thomas" />

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.<ref name="thomas" />

===Physiological effects of unprotected space exposure===
{{Main|Space exposure}}
The human body can briefly survive the hard vacuum of space unprotected,<ref name="Bellows2006">{{cite web |url=http://www.damninteresting.com/outer-space-exposure |title=Outer Space Exposure |last=Bellows |first=Alan |date=November 27, 2006 |website=Damn Interesting |id=Article #237 |access-date=June 19, 2013}}</ref> despite contrary depictions in some popular [[science fiction]]. Consciousness is retained for up to 15 seconds as the effects of [[Hypoxia (medical)|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.<ref name="Springel 2013" >{{cite web|date=30 July 2013 |first=Mark|last=Springel |publisher=Harvard University Graduate School of Arts and Sciences |url=https://sitn.hms.harvard.edu/flash/2013/space-human-body/ |title=The human body in space: Distinguishing fact from fiction |access-date=6 October 2023}}</ref>

In space, there are highly energized [[subatomic particle]]s 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.<ref name=thomas>{{cite book|last1=Thomas|first1=Kenneth S.|last2=McMann|first2=Harold J.|title=U.S. Spacesuits|date=23 November 2011|publisher=Springer Science & Business Media |isbn=978-1-4419-9566-7 }}</ref><ref>{{cite web|title=Space Radiation Analysis Group|url=http://srag.jsc.nasa.gov/Index.cfm|website=NASA, Johnson Space Center|publisher=NASA|access-date=16 February 2015|archive-url=https://web.archive.org/web/20150218045538/http://srag.jsc.nasa.gov/Index.cfm|archive-date=February 18, 2015}}</ref>

Temperature in space can vary extremely depending on the exposure to radiant energy sources. Temperatures from solar radiation can reach up to {{convert|250|°F}}, and in its absence, down to {{convert|-387|°F|0}}. Because of this, space suits must provide sufficient insulation and cooling for the conditions in which they will be used.<ref name=thomas/>

The vacuum environment of space has no pressure, so gases will expand and exposed liquids may evaporate. Some solids may [[Sublimation (phase transition)|sublimate]]. It is necessary to wear a suit that provides sufficient internal body pressure in space.<ref name=thomas/><ref>{{cite book|last1=Hanslmeier|first1=Arnold|title=The Sun and Space Weather|date=1 January 2002|publisher=Springer Science & Business Media|isbn=1-4020-0684-5|pages=166–67|edition=Illustrated}}</ref> The most immediate hazard is in attempting to hold one's breath during [[Uncontrolled decompression#Explosive decompression|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 chamber]]s).<ref name="Bellows2006" /><ref>{{cite web |url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html |title=Ask an Astrophysicist: Human Body in a Vacuum |website=Image the Universe! |publisher=[[NASA]] |access-date=December 14, 2008}}</ref> Human skin does not need to be protected from vacuum and is gas-tight by itself.<ref name="Springel 2013" /> 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 gas]]es, known as a [[space activity suit]] (SAS).{{clarify|how does this affect breathing?|date=September 2023 }}{{citation needed|date=October 2023}}<!-- uncontroversial but I can't remember the sources right now. It is probably in Thomas, but I don't have access-->