- Space exposure
Space exposure is in reference to the exposure of a human to the conditions of
outer space , without protective clothing and beyond the Earth’s atmosphere in avacuum .Explanation and history of space exposure
The key concerns for a human without protective clothing beyond Earth’s atmosphere are the following, listed roughly in the ascending order of mortal significance:
ebullism ,hypoxia ,hypocapnia ,decompression sickness , extreme temperature variations and cellular mutation and destruction from high energy photons and (sub-atomic) particles.Pilmanis, Andrew A. and Sears, William J. (2003), [http://dx.doi.org/10.1016/S0140-6736(03)15059-3 doi 10.1016/S0140-6736(03)15059-3] ]Ebullism, hypoxia, hypocapnia and decompression sickness
Ebullism , the formation of bubbles in body fluids due to reduced ambient pressure, is the most severe component of the experience. Technically, ebullism is considered to begin at an elevation of around convert|19|km or pressures less than 6.3 kPa (47 mm Hg). Experiments with other animals have revealed an array of symptoms that could also apply to humans. The least severe of these is the freezing of bodily secretions due toevaporative cooling . But severe symptoms such as loss ofoxygen in tissue (anoxia ) and multiplicative increase of body volume occur within 10 seconds, followed by circulatory failure andflaccid paralysis in about 30 seconds. The lungs also collapse (atelectasis ) in this process, but will continue to release water vapour leading to cooling and ice formation in therespiratory tract .A rough estimate is that a human will have about 90 seconds to be recompressed, after which death may be unavoidable.Landis, Geoffrey A. [http://www.sff.net/people/geoffrey.landis/vacuum.html website] ] The absence of oxygen outside the body causing rapid de-oxygenation of the blood (hypoxia) is the primary reason for unconsciousness within 14 seconds.NASA [http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html technical report] ] If a person is exposed to low pressures more slowly, hypoxia causes gradual loss of cognitive functions starting at about convert|3|km|ft|sigfig=1 altitude equivalent. Less severe effects include the formation of
nitrogen gas bubbles and consequent interference with organ function (decompression sickness ), which is actually less severe in space than in diving. Meanwhile, reduction of bloodcarbon dioxide levels (hypocapnia ) can alter the bloodpH and indirectly contribute to nervous system malfunctions. If the person tries to hold their breath during decompression, the lungs may rupture internally.Few humans have experienced these four conditions.
Joseph Kittinger experienced localised ebullism during a convert|31|km ascent in ahelium -driven gondola. His right-hand glove failed to pressurise and his hand expanded to roughly twice [PBS [http://www.pbs.org/wgbh/nova/escape/skydive.html report] ] its normal volume accompanied by disabling pain. His hand took about 3 hours to recover after his return to the ground. Two other people were decompressed accidentally during space mission training programs on the ground, but both incidents were less than 5 minutes in duration, and both victims survived.International Space Station andSpace Shuttle astronauts regularly work inExtravehicular Mobility Unit s (EMUs orspace suits ) that are at pressures less than 30% of the spacecraft to facilitate mobility, without experiencing noticeable decompression sickness.Stewart, L. et al. (2007), [http://dx.doi.org/10.1016/j.jemermed.2006.05.031 doi 10.1016/j.jemermed.2006.05.031] ] Nevertheless, the decompression accident ofSoyuz 11 killed all three cosmonauts on board. [ Time Magazine [http://www.time.com/time/magazine/article/0,9171,903011-1,00.html 1971] ]Decompression is a serious concern during the extra-vehicular activities (EVAs) of astronauts.Conkin, Johnny (2001), [http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-2001-210196.pdf NASA technical report] ] Current EMU designs take this and other issues into consideration, and have evolved over time.Jordan, Nicole C. et al. (2005), [http://dx.doi.org/10.1109/RE.2005.69 doi 10.1109/RE.2005.69] ] Jordan, Nicole C. et al. (2006), [http://dx.doi.org/10.1016/j.actaastro.2006.04.014 doi 10.1016/j.actaastro.2006.04.014] ] A key challenge has been the competing interests of increasing astronaut mobility (which is reduced by high-pressure EMUs, analogous to the difficulty of deforming an inflated balloon relative to a deflated one) and minimising decompression risk. Investigators Gorguinpour, Camron (2001), [http://www.lpi.usra.edu/publications/reports/CB-1106/ucb01.pdf] have considered pressurising a separate head unit to the regular 71 kPa (10.3 psi) cabin pressure as opposed to the current whole-EMU pressure of 29.6 kPa (4.3 psi) [for reference, the atmospheric pressure at sea level is 101.4 kPa, equal to 14.7 psi – [http://www.britannica.com/eb/article-9010121/atmospheric-pressure Britannica] ] ). In such a design, pressurisation of the torso could be achieved mechanically, avoiding mobility reduction associated with pneumatic pressurisation.
Extreme temperature variations
Extreme temperature variations are a problem in space, because heat exchange occurs primarily via infrared radiation. While the absence of convection and conduction causes an insulating effect preventing rapid dissipation of body heat, localized heating can occur if exposed to starlight at distances comparable to the Earth-Sun distance.
Cellular mutation and destruction from high energy
photons and (sub-atomic) particlesA more severe long-term effect would be the direct exposure to high energy photons (ultraviolet, X-ray, and gamma) and energized subatomic particles (primarily protonsBoynton, W. V. et al. (2004), [http://dx.doi.org/10.1023/B:SPAC.0000021007.76126.15 doi 10.1023/B:SPAC.0000021007.76126.15] ] ). These can permanently denature
DNA and other cellular molecules through atomic and nuclear interactions. Prolonged exposure and the ability of X and gamma photons to penetrate the entire body may cause death from organ failure, while even short-term exposure may cause cancer.Fact|date=December 2007In science fiction
Spacing is a staple of
science fiction , where it usually occurs as a method of execution (or other sort ofkilling ) byvacuum exposure in space - usually accomplished by ejecting the subject through theairlock of aspacecraft orspace station without aspace suit . The primary cause of death would beasphyxia . Many films show people exposed to vacuum in unrealistic ways.
*Most movies, such asOutland , show people exploding in a vacuum.
*,A Trip to the Moon ,From the Earth to the Moon , and several episodes ofDoctor Who show people surviving a vacuum with no suit on.
*Battlestar Galactica and the film Sunshine, show some people suffering after a short exposure, and others dying plus freezing from longer exposure.
*InTotal Recall , the character of Douglas Quaid can survive near-vacuum conditions just by holding his breath.
*Several recent films, such asMission to Mars , show people freezing instantly in a vacuum.
*In the episodeTangent , on the TV showStargate SG1 , Col. Jack O'Neil and Teal'c have to escape a Goa'uld death glider by exiting the cockpit in the middle of space and are brought aboard a Tok'ra scout ship through the ring transporter. When they are on the ship they are perfectly fine even after being exposed to space for about five secondsee also
*
Human adaptation to space References
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