Space exposure

Space exposure is the subjection of a human to the conditions of outer space, without protective clothing and beyond the Earth’s atmosphere in a vacuum.

Explanation and history

The key concerns for a human without protective clothing beyond Earth’s atmosphere are the following, listed roughly in the descending 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.[1]

For the effect of rapid decompression to vacuum conditions, see the main article Uncontrolled decompression.

Ebullism, hypoxia, hypocapnia and decompression sickness

Ebullism, the formation of bubbles in body fluids due to reduced ambient pressure,[2] is the most severe component of the experience. Technically, ebullism is considered to begin at an elevation of around 19 kilometres (12 mi) or pressures less than 6.3 kPa (47 mm Hg),[2] known as the Armstrong Limit.[1] 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 to evaporative cooling. But severe symptoms such as loss of oxygen in tissue (anoxia), followed by circulatory failure and flaccid paralysis in about 30 seconds.[1] The lungs also collapse (atelectasis) in this process, but will continue to release water vapour leading to cooling and ice formation in the respiratory tract.[1]

A rough estimate is that a human will have about 90 seconds to be recompressed, after which death may be unavoidable.[2][3] Unconsciousness is likely to occur within 14 seconds, primarily due to the much lower pressure outside the body causing rapid de-oxygenation of the blood (hypoxia).[4] In 1966 NASA volunteer test subject Jim LeBlanc lost consciousness after approximately 15 seconds of being accidentally depressurised in a ground-based depressurization chamber.[5] If a person is exposed to low pressures more slowly, hypoxia causes gradual loss of cognitive functions starting at about 3 kilometres (10,000 ft) altitude equivalent. Less severe effects include the formation of nitrogen gas bubbles and consequent interference with organ function (decompression sickness), which is less severe in space than in diving. Meanwhile, reduction of blood carbon dioxide levels (hypocapnia) can alter the blood pH and indirectly contribute to nervous system malfunctions. If the person tries to hold their breath during decompression, the lungs may rupture internally.[3]

Dobrovolskiy, Volkov and Patsayev, the only victims of space decompression

Few humans have experienced these four conditions. In 1960, Joseph Kittinger experienced localised ebullism during a 31 kilometres (19 mi) ascent in a helium-driven gondola.[1] His right-hand glove failed to pressurise and his hand expanded to roughly twice its normal volume[6][7] 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.[1] International Space Station and Space Shuttle astronauts regularly work in Extravehicular Mobility Units (EMUs or space suits) that are at pressures less than 30% of the spacecraft to facilitate mobility, without experiencing noticeable decompression sickness.[8] However, EMUs are pressurized with pure oxygen as to maintain an oxygen partial pressure equivalent with the 1 atm nitrogen-dominated ISS atmosphere. Significant prebreathing and decompression procedures are required when donning an EMU in order to avoid decompression sickness.

The only known humans to have died of space exposure are the three crew members of the Soyuz 11 spacecraft: Vladislav Volkov, Georgi Dobrovolski and Viktor Patsayev. During re-entry on June 30, 1971, the ship's depressurization resulted in the death of the entire crew.[8][9]

Decompression is a serious concern during the extra-vehicular activities (EVAs) of astronauts.[10] Current EMU designs take this and other issues into consideration, and have evolved over time.[11][12] 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[13] have considered pressurizing 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).[12][14] In such a design, pressurization of the torso could be achieved mechanically, avoiding mobility reduction associated with pneumatic pressurization.[13]

Cellular mutation and destruction from high energy photons and (sub-atomic) particles

A more severe long-term effect is the direct exposure to high energy photons (ultraviolet, X-ray, and gamma) and energized subatomic particles (primarily protons[15]).

In science fiction

Spacing is a staple of science fiction, where it often occurs as a method of execution (or other sort of killing) by vacuum exposure in space — usually accomplished by ejecting the subject through the airlock of a spacecraft or space station without a space suit. Spacing is sometimes used as a means of dispatching enemies, usually by luring or herding the target(s) into an airlock, hangar or cargo bay with an exterior hatch and then flushing them out into space, or opportunistically double-opening an airlock—or even blowing out a window or hull panel—that happens to be near the target, with similar results. The primary cause of death would be asphyxia. An example can found in the novel 2001: A Space Odyssey by Arthur C. Clarke in which astronaut David Bowman is exposed to the vacuum of space inside the Discovery One spacecraft after the computer controlling its life support malfunctions and opens the doors of the airlock.[16] A passage in the novel claims,

Like any properly trained man in good health, he could survive in vacuum for at least a minute - if he had time to prepare for it. But there had been no time; he could only count on the normal fifteen seconds of consciousness before his brain was starved and anoxia overcame him. Even then, he could still recover completely after one or two minutes in vacuum - if he was properly recompressed; it took a long time for the body fluids to start boiling, in their various well-protected systems.[17]

See also

References

  1. 1 2 3 4 5 6 Pilmanis, Andrew; William Sears (December 2003). "Physiological hazards of flight at high altitude". The Lancet. 362: s16–s17. doi:10.1016/S0140-6736(03)15059-3.
  2. 1 2 3 Billings, Charles E. (1973). "Chapter 1) Barometric Pressure". In James F.; West, Vita R. Bioastronautics Data Book (PDF) (Second ed.). NASA. pp. 2–5. NASA SP-3006. Retrieved 2012-09-23. "33.1 MB". 33.1 MB
  3. 1 2 Landis, Geoffrey (7 August 2007). "Human Exposure to Vacuum". Retrieved 2006-03-25.
  4. ↑ NASA Ask an Astronomer
  5. ↑ "The Space Suit". Moon Machines. Season 1. Episode 5. 2008. Science Channel.
  6. ↑ Higgins, Matt (May 24, 2008). "20-Year Journey for 15-Minute Fall". The New York Times (online). p. 2. Retrieved 2012-09-23.
  7. ↑ "Skydive from the Stratosphere", NOVA Online, Public Broadcasting Service(PBS). November 2000. Retrieved 2012-09-23
  8. 1 2 Stewart, L. et al. (2007), doi 10.1016/j.jemermed.2006.05.031
  9. ↑ "Science: Triumph and Tragedy of Soyuz 11". Time Magazine. Time Inc. July 12, 1971. Retrieved 2012-09-23. (subscription required)
  10. ↑ Conkin, Johnny (January 2001), "Evidence-Based Approach to the Analysis of Serious Decompression Sickness With Application to EVA Astronauts" NASA TP-2001-210196. Retrieved 2012-09-23. "5.88 MB". 5.88 MB
  11. ↑ Jordan, Nicole C.; Saleh, J.H.; Newman, D.J. (2005), "The Extravehicular Mobility Unit: case study in requirements evolution". doi 10.1109/RE.2005.69. Requirements Engineering, 2005. Proceedings.13th IEEE International Conference, pp.434-438. Retrieved on 2012-09-23 (subscription required)
  12. 1 2 Jordan, Nicole C.; Saleh, Joseph H.; Newman, Dava J. (2006). "The extravehicular mobility unit: A review of environment, requirements, and design changes in the US spacesuit". Acta Astronautica. 59 (12): 1135–1145. Bibcode:2006AcAau..59.1135J. doi:10.1016/j.actaastro.2006.04.014. Retrieved 2011-09-07.
  13. 1 2 Gorguinpour, Camron et. al (2001), LPI "Advanced Two-System Space Suit". University of California, Berkeley CB-1106. Retrieved 2012-09-23. "95 KB". 95 KB
  14. ↑ for reference, the atmospheric pressure at sea level is 101.4 kPa, equal to 14.7 psi – Britannica
  15. ↑ Boynton, W. V. et al. (2004), doi 10.1023/B:SPAC.0000021007.76126.15 (subscription required)
  16. ↑ Landis, Geoffrey. "Vacuum Exposure in Science Fiction". Retrieved 9 June 2017.
  17. ↑ Clarke, Arthur C.: "2001: A Space Odyssey"
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