Updated Monday, 31-Oct-2005 11:29:55 EST
Living in Space
standard atmosphere composition:
- Physiological Considerations
- Space accommodation syndrome (SAS) -- disorientation, loss of appetite, nausea, vomiting, diarrhea
- muscular atrophy -- loss of muscle bulk and tone -- can compensate by strenuous aerobic workouts of 8-16 hours per day!
- bone decalcification (similar to osteoporosis in the elderly) -- bones lose 1-2% of their calcium for each month in orbit -- bones become weaker and calcium levels in blood rise (bad for heart)
- Earth's atmosphere protects us from much harmful radiation
- Van Allen belts and solar flares increase radiation exposure
- Measures of radiation
- rad -- radiation absorbed dose -- natural exposure on Earth is 0.2 rad/year
- rem -- radiation equivalent mammal -- this measure uses a correction factor known as radiation biological effectiveness (RBE) to correct the rad measure for different forms of radiation (particles vs X-rays, etc)
- Sievert (Sv) -- similar to rem -- includes correction factors for type of radiation and part of the body that is irradiated. 1 Sv = 100 rems.
- roentgen -- 1 roentgen is approximately the same as 1 rad for X-rays passing through soft living tissue
- Natural exposure (from geological materials, cosmic radiation, and remnant materials
from nuclear weapons testing) is approximately 3.5 mSv/yr (milliSieverts/year), equivalent to 0.35 rems/yr.
Human Tolerances to Radiation Over Time
(Dose is in roentgens.)
Note that a larger dose can be tolerated if accumulated over a long period of time (body has time to repair some of the damage).
- metal walls of Space Shuttle, Mir, etc. are good shields
- best shield would be lead, but it's too heavy to use efficiently in spacecraft
- aluminum works reasonably well -- can be combined with thin layers of gold, tantalum, cadmium, rhodium, or platinum
- minimize time astronauts spend outside the spacecraft
- nitrogen -- 78.09%
- oxygen -- 20.95%
- argon -- 0.93%
- carbon dioxide and other trace elements -- 0.03%
Problems with nitrogen
- figure shows relationship between percentage of O2 and atmospheric pressure
- dangerous region -- insufficient pressure to get enough O2 into blood to sustain life.
- safe region -- lower percentage of O2 permitted if pressure is high, but at lower pressure, need greater percentage of O2
- unsafe region -- okay for short periods (several hours), but otherwise, high percentage of O2 at high pressure will cause disorientation and is also a fire hazard.
- hypoxia -- shortage of oxygen in blood
- anoxia -- condition of insufficient oxygen to sustain life
Problems with carbon monoxide (CO) and carbon dioxide (CO2)
- nitrogen gas dissolved in blood will "boil" (actually evolve from blood when body experiences rapid decrease in external atmospheric pressure -- same effect as sudden release of bubbles when a carbonated drink is opened
- can flush nitrogen from blood with pure oxygen (so-called prebreathing) prior to donning low pressure space suit
- can also slowly reduce cabin pressure over a period of several hours before
putting on space suits
- space suit cannot easily contain a higher pressure without leaking -- experimental high-pressure suits exist, but they contain rigid shells that make it difficult for astronauts to move
- can replace some nitrogen in the cabin atmosphere with helium, which does not dissolve in blood
- CO poses great danger, even in small amounts where there is ample oxygen present, since CO is more readily absorbed by red blood cells and thus prevents adequate oxygen absorption
- CO generated by incomplete combustion (electrical fires or overheated components containing almost any carbon compounds
- use lithium hydride crystals in canisters -- air circulation system passes air through canisters, CO is adsorbed to surfaces of lithium hydride crystals
- can bake off the CO in ovens when canisters are returned to Earth, and then use them again
- accumulation of CO2 results in narcosis (drowsiness,
light-headedness, and eventual loss of consciousness -- if the concentration
becomes too high, it can be fatal)
- use potassium compounds to adsorb CO2 -- same procedure as for lithium hydride and CO.
identical panels, instrument arrangements may be efficient for engineering, but these are bad for psychological well-being of the crew -- need to vary the appearance of the equipment and interior surfaces, make these visually appealing.
provide an area of privacy (even if very small) for each astronaut
choose crew makeup carefully to ensure compatibility of personalities
allow crew certain expressions of individuality (choice of clothing, personal items, decor of living quarters, etc.)
- 1 - 7 days, environment not critical -- like a camping trip -- humans can tolerate discomfort reasonably well
- after 14-30 days, psychological depression can begin
Copyright © 1998, Robert G. Melton
Updated Monday, 31-Oct-2005 11:29:55 EST