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Pressurization and Atmospheric Constituents

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Too much Oxygen = Embolism. Too little Oxygen = Hypoxia. History ... Long term use is prohibited because of the risk of oxygen toxicity, or embolism. ... – PowerPoint PPT presentation

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Title: Pressurization and Atmospheric Constituents


1
Pressurization and Atmospheric Constituents
  • Matt Estes
  • Component Research Presentation

2
Introduction
  • The purpose of this presentation is evaluate the
    current means of gaseous pressurization and the
    particular elements used to do so.

3
Introduction
  • I researched this topic over the summer, reading
    through the bioastronautics data book, and this
    seemed like the natural progression for my field
    of research.

4
Background
  • Why do we need suit pressurization?
  • Because in a low pressure environment the body
    would experience painful swelling or even death.

5
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6
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7
Background
  • Why do we need oxygen?
  • Metabolism, its serves as the bodys primary
    electron receptor.
  • Its a careful balance however
  • Too much Oxygen Embolism
  • Too little Oxygen Hypoxia.

8
History
  • The first pressurized suits were developed for
    divers, and this technology was later amended for
    use in high altitude flying and then for use in
    space.
  • For most of their history contained atmospheres
    have used solely Nitrogen and Oxygen, the 8020
    gaseous mixture found here on Earth.

9
History
  • The pressure used was always that of Earths
    atmosphere.
  • It is only recently that space suits have begun
    to use pressures under 101.4 kPa.

10
Topics of Discussion
  • I dissected the pressurization system up into 4
    categories I could use to compare it to
    alternative suit designs
  • Advantages
  • Entrenchment (huge subset of Advantages)
  • Disadvantages
  • Constants

11
Advantages
  • Sound attenuation
  • Airlock time
  • Leakage
  • Energy

12
Sound Attenuation
  • If a lower pressure system was used, beyond a
    certain limit this would prevent all vocal
    communication.
  • Helium is the frontrunner in the race to find an
    alternative means of gaseous pressurization.
  • Unfortunately, it also makes you sound like Tiny
    Tim on methamphetamines.

13
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14
Sound Attenuation
  • It has been shown that adding Neon to a
    Helium-Oxygen gas mixture can help curb the
    degree of sound attenuation, but this would
    lessen the amount of weight saved by using Helium
    in the first place.
  • With Nitrogen and the current degree of
    pressurization we notice no difference at all
    because it is what we are used to.

15
Airlock Time
  • A switch to Helium at a lower pressure would
    require more time spent in the airlock before
    each EVA.
  • This is not ideal for a mission requiring
    frequent trips on the surface.

16
Leakage
  • I am reviewing the mode of gaseous pressurization
    only, and while it is true that much leakage
    could be saved were a counter pressure suit used,
    that will not be discussed here.
  • The comment I have to make is remarkably
    intuitive, but requires mentioning just the same.

17
Leakage
  • Helium is a much smaller gas than Nitrogen, and
    if used as a dilutent would escape much more
    easily than Nitrogen through micropuntures in the
    suit.
  • This would require that more gas be brought along
    and more energy be expended pumping gas into the
    suit.

18
Leakage
  • Not only that, but it would increase the risk of
    contaminating the martian surface.

19
Energy
  • The air in the suit is also used to help cool the
    Primary Life Support System (PLSS).
  • If the pressure were reduced, significantly more
    air would have to be pumped over the PLSS to
    achieve the same rate of cooling, requiring more
    energy.

20
Entrenchment
  • Perhaps the primary reason for retaining the
    current means of suit pressurization is that it
    is entwined with so many other facets of the
    mission.
  • These include
  • Metabolism
  • Photosynthesis
  • Physical Parameters
  • Mission Parameters

21
Metabolism
  • Some of the metabolic factors that would be
    affected by a change in pressure or atmosphere
    are
  • Antibody production
  • Susceptibility to viral infection
  • Recovery time from infection
  • gas exchange

22
Photosynthesis
  • Some of the photosynthetic factors that would be
    affected by a change in pressure or atmosphere
    are
  • Water loss by transpiration
  • Production of toxic gases

23
Physical Parameters
  • Some of the physical parameters that would be
    affected by a change in pressure or atmosphere
    are
  • Use of negative pressure as a means of material
    containment
  • Solubility and/or chemical composition
  • Acoustics

24
Physical Parameters
  • Combustion and chemical reaction (Increased
    flammability)
  • Heat transfer through surrounding air

25
Mission Parameters
  • Some of the mission parameters that would be
    affected by a change in pressure or atmosphere
    are
  • Materials selection
  • Air cooling of equipment
  • Sound levels
  • Increased testing of materials
  • Commonality with other space programs

26
  • Thus far the nitrogen-oxygen, high pressure
    system has appeared well suited to our needs, but
    this is not entirely the case

27
Disadvantages
  • Weight
  • Nitrogen Bubbling
  • Prebreath time
  • Energy

28
Weight
  • The current EMU weighs 300 pounds on Earth,
    equivalent to 100 pounds in Martian gravity.
  • This is not a tolerable amount for extended EVAs
    on a planetary surface.
  • If Helium was used as the diluting gas, and the
    pressure was reduced, this would help lessen the
    load.

29
Weight
  • The current suit utilizes the 101.4 kPa
    nitrogen-oxygen mixture found on Earth.
  • Of that, only 21.4 is metabolically required
    Oxygen.
  • The rest is Nitrogen, and prototype suits in
    development have supposedly worked the total
    pressure down to 57.2 kPa.

30
Weight
  • This is a substantial reduction in weight, but it
    might be possible with Helium to reduce the
    weight even more.

31
Nitrogen Bubbling
  • The transition from a high pressure habitat to a
    low pressure suit causes the nitrogen dissolved
    in the blood to return to a gas phase.
  • The bubbling within the blood, frequently
    experienced by divers, is quite painful and can
    lead to death if the pressure drop is severe
    enough.

32
Nitrogen Bubbling
  • Helium has the advantage of being poorly soluble
    in blood.
  • This means that less Helium would dissolve in the
    blood at high pressure, and in turn, less helium
    would gas out of the blood in low pressure.

33
Prebreath Time
  • The current means of dealing with the bends is to
    spend a significant amount of time prebreathing
    one hundred percent oxygen during a washout
    period before transitioning between the 101,4 kPa
    shuttle and the 29.6 kPa EMU suit.
  • The transition from habitat to suit can be
    accomplished one of two ways

34
Prebreath Time
  • The first requires prebreathing pure oxygen for
    four hours before the EVA.

35
Prebreath Time
  • The second requires prebreathing one hundred
    percent oxygen for one hour at 101.4 kPa, then
    lowering the cabin pressure to 70.3 kPa for 24
    hours, and finally prebreathing one hundred
    percent oxygen in the EMU suit for forty minutes
    prior to EVA.

36
Prebreath Time
  • The current shuttle mission plan uses the latter
    method of successive drops in pressure.
  • This has the advantage of being able to be
    carried out while the crew is active, rather than
    forcing them into an airlock for multiple hours
    at a time.

37
Prebreath Time
  • But the length of this cycle is not plausible for
    a Martian expedition requiring daily excursions
    to the planetary surface.

38
Energy
  • The use of Nitrogen within the suit requires that
    vast amounts be brought from Earth.
  • This is extremely costly, as it necessitates the
    use of much more fuel.

39
Energy
  • If the suit were compartmentalized into body and
    head, the carbon dioxide rich atmosphere of Mars
    could be used for pressurization of the torso and
    extremities.
  • This would save millions in fuel costs.

40
Constants
  • Diluting Gas
  • Water Vapor
  • Carbon Dioxide

41
Diluting Gas
  • As mentioned previously, one hundred percent
    oxygen atmospheres have been used, but only for
    short periods of time.
  • Long term use is prohibited because of the risk
    of oxygen toxicity, or embolism.
  • This is prevented by the use of a diluting gas,
    the current one being Nitrogen.

42
Diluting Gas
  • Current research is underway to determine the
    lower bounds of acceptable Nitrogen
    concentration.
  • Diluting Gas is also required for proper lung
    ventilation.

43
Diluting Gas
  • Were a pure oxygen atmosphere used, poorly
    ventilated air sacs within the lungs might
    collapse because they absorbed all the oxygen
    they contained before new oxygen arrived.
  • The diluting gas helps prevent this by providing
    volume that helps keep the ventilation pathways
    open.

44
Water Vapor
  • The pressure of water vapor with the suit is kept
    between one and two kPa.
  • The minimum value is dictated by the amount of
    water required to moisten the lungs

45
Water Vapor
  • The upper bounds of water vapor pressure is
    necessitated by the fact that increased water
    within the system leads to an exponential
    increase in the rate of corrosion.

46
Carbon Dioxide
  • The acceptable pressure of carbon dioxide is
    quite variable and is allowed to fluctuate as
    long as it is kept below one kPa.
  • This leads to some leeway on how stringent the
    filtration process must be, and it is generally
    accepted that it should be allowed at a near
    maximum because this reduces the energy costs of
    removing it.

47
Disposal
  • Both carbon dioxide and water are jettisoned
    from the suit into the environment.
  • This wasteful, and and creates a dangerous risk
    of contamination
  • If weight constraints allow, these should be
    returned to the habitat where they could help
    with plant growth.

48
What This Means
  • The use of the Nitrogen-Oxygen mixture at high
    pressure has some definite problems.
  • But it has its advantages as well.
  • I cant say if one is definitively better than
    the other, nor do I think can anyone else.

49
Reccomendation
  • I do think that the use of helium as a dilutent
    gas, and other alternatives such as suit
    compartmentalization, mechanical counter
    pressure, and closed cell foam should be explored
    for their potential advantages.

50
Reccomendation
  • It seems that any development costs incurred here
    on Earth would far outweigh the in situ costs of
    using second rate technology during the mission.
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