Friday, January 15, 2016

Astronaut Facing Drowning Points Out Need for Better Space Suit

Note updates 1-29-16 in red below.

Astronauts Tim Peake and Tim Kopra were forced to cut short an EVA due to water leaking into Kopra’s helmet.  This is the very same suit worn by astronaut Parmitano in 2013,  who nearly drowned from a water leak into the helmet.  That suit was extensively refurbished after the 2013 incident,  but clearly there is still a risk associated with its water cooling system.

So,  do all spacesuits need water cooling systems?  No.  The fundamental job is providing a way for you to breathe,  and surprisingly enough,  that does not necessarily mean protecting you from exposure to vacuum.

As long as your heart is beating and your blood pressure hasn’t zeroed,  exposure to vacuum is not fatal and your blood does not boil.  Nothing “explodes” either.  Nor do you instantly freeze or fry,  something that takes longer than anoxia death in vacuum.  The various science fiction shows have lied to you. 

You will start to die within about 2 minutes or so of whole-body exposure to vacuum,  because of nothing more than anoxia,  since oxygen at zero pressure will not diffuse across your lung membranes into your blood. 

In point of fact,  the reverse diffusion of oxygen from your blood to the environment in vacuum is quite enhanced over what we normally experience down here on the surface of the Earth.  So anoxia sets-in quicker upon exposure to vacuum “out there”,  than it does by gross strangulation down here (usually about 4 minutes,  but it can take twice that long,  depending upon your initial blood oxygen levels). 

In experiments and accidents,  people and animals have survived whole-body exposure to vacuum for up to about 2 minutes.  And that’s a fact,  Jack!  This has been known since the 1960’s. 

What’s minimally required to survive in space is an oxygen supply at sufficient pressure to cause adequate diffusion of oxygen across the lung membranes into the blood.  Nothing more than that.  For most folks,  this is in the neighborhood of 2-3 psi pressure of pure oxygen,  or 2-3 psi “partial pressure” of oxygen in a more complicated atmosphere. 

Sea level air has just about 3 psi partial pressure of oxygen,  while air at 10,000 feet elevations has about 2.1 psi.  Some folks are adapted to 15,000,  even 20,000 foot elevations.   That last is about 1.4 psi partial pressure of oxygen.  That’s about the utter minimum for survivable breathing gas pressure,  even if pure oxygen.  But it is based on actual people living active lives at such conditions.

The most immediate idea that comes to mind is just to breathe oxygen at 2 to 3 psi pressure,  with a mask sealed tightly to your face.  This is called "pressure breathing".  
There is an immediate danger with "pressure breathing":  if oxygen pressure in the lungs exceeds about 2 psi without counterbalancing pressure within the body,  the lung tissues rupture in an event called "pneumo-thorax".  This is fatal and irreversible and immediate,  you drown in your own blood.  It is a well known risk among scuba divers.

There is a another complication that requires time:  counter-pressure must be exerted upon the body that is more-or-less equal to the breathing gas pressure,  or else those breathing gases will diffuse out of the blood into the spaces between cells in the body,  causing swelling,  disability,  even death.  We have known that since the late 1940’s.

It takes about 30 minutes for significant swelling to happen to a vacuum-exposed small body part like a hand or foot.  It happens much quicker (5-10 minutes) if the whole body is uncompressed while breathing oxygen at pressure.  We learned these figures by hard experience,  since the late 1940’s.  They are accurate. 

There is also a mitigating factor:  the body “does not care one whit” how this counterbalancing pressure is applied!  It can be the pressure of the gas within the current modern space pressure suit,  or it can be a mechanical “squeeze” exerted by other means,  as long as it is applied whole-body.  Pressure is pressure,  no matter how it is applied! 

Our cells are essentially little water balloons:  the pressure in them,  and between them,  goes up whether we put them inside a container at some gas pressure,  or if we simply grab them and physically squeeze them (like a water balloon) in our hands.  Doesn’t matter,  as long as it gets done.

Modern space suits are what we call “full pressure suits”,  which means they are literally gas-tight balloons whose internal gas pressure is the compression the body needs to counterbalance the breathing gas pressure.  These suits isolate you chemically and thermally from your environment;  one layer is quite literally a gas-impermeable rubber balloon.  

It is difficult at best to expel from such a suit the heat your body produces,  especially if you are active.  Your breath and your sweat fill your suit (and your helmet) with moisture,  thus fogging your visor.  There is also carbon dioxide to absorb.  We have fully understood this since the 1950’s at the very latest.  Our first efforts date to the 1930’s. 

The heat problem requires water-cooled underwear to carry your body heat to your backpack,  where some sort of “air conditioner” equipment expels that heat to space.  Likewise,  your breathing gas requires considerable regeneratable dessicant to get rid of the moisture load from your breath,  and more especially,  your body sweat (the larger of the two sources).    The carbon dioxide absorbent also needs to be regeneratable. 

Your makeup oxygen supply is not lightweight,  all by itself,  although makeup from a flask of liquid oxygen is the most efficient.  The combination of all this plus adequate insulation against hot and cold makes your suit,  and your life support backpack,  quite heavy.  It’s been like that since the 200+ pound Apollo moonsuit,  all through the space shuttle program (300+ pounds),  and is still like that on the international space station (ISS) today (close to 400 pounds). 

But,  what if you relied on mechanical-physical compression by a tight garment instead?  This was exactly how the early “partial pressure” suits worked,  and they worked quite well,  actually,  for 10-minute bailouts,  beginning in the late 1940’s.  Hands and feet were uncompressed,  and compression over the limbs and body was rather uneven,  but it worked for 10 minutes anyway. 

Such a compression garment need not hold gas pressure at all,  it can be entirely porous!  You can sweat right through it into vacuum,  which is actually more efficient cooling than here on Earth,  because of inherent moisture vaporization into vacuum.  So you need no mechanical cooling system at all,  and your moisture load is only breath,  not breath-plus-sweat.  Your life support backpack reduces to just the makeup oxygen,  plus minimal dessicant,  and the same carbon dioxide absorbent. 

You still need protection against hot and cold,  but this can be an over-garment.  It simply need not be part of your compression garment!  Think vacuum-protective underwear,  overlain by whatever insulation,  at whatever level you need,  for the job at hand. 

That gives you the freedom to dress in layers,  just like down here on Earth!  In point of fact,  you can use ordinary Earth garments for this insulation function.  Coveralls,  aprons,  coats,  pants,  shoes,  and gloves,  all exactly the same as we wear down here. 

Believe it or not,  this notion of vacuum-protective underwear (known as “mechanical counter-pressure” or “MCP”) was tested and somewhat-developed in the late 1960’s,  quite successfully,  by Dr. Paul Webb.  The compression garment,  breathing helmet,  and oxygen backpack that he tested totaled 85 pounds. In its final form,  the difficulty of breathing while wearing a very tight garment was eased by incorporating a breathing tidal-volume bag on the chest within a non-elastic restraining jacket,  instead of garment compression.

Add 5-15 lb of insulating garments,  gloves,  and boots,  and you are talking about a spacesuit that weighs around 100 pounds,  not the 300-400 pounds currently in use!  Plus,  it is a whole lot more dexterous:  you can bend sharply over,  climb ladders,  and crawl into small spaces,  something not at all possible with a “normal” modern spacesuit. If you fall over in a 400 pound full pressure suit,  it is likely you cannot get up on your feet again very effectively.  If there is no one close by,  you may lay there till you die.  That doesn't happen in a supple,  100-pound MCP suit.

This stuff worked long ago:  I have seen the 1968-vintage video of Dr. Webb’s test subject in a vacuum tank,  pedaling a bicycle ergonometer for half an hour,  and wearing nothing but 6-7 layers of tight pantyhose material and a breathing helmet.  The simulated altitude was 87,000 feet,  where even a pure oxygen atmosphere would still only be 0.293 psia.  If there were a problem with this approach,  it would have shown up in that half an hour:  no problems showed up! 

This test effort was partially-funded by NASA:  they have known that this alternative works for almost half a century.  Irrational attitudes and monied interests,  not actual facts,  prevent its application today.  Small amounts of grant money to Dr. Dava Newman at MIT have supported some work on this “MCP” suit concept,  but nothing at any of NASA’s favored spacesuit contractors.  Dr. Newman has since been hired by NASA,  but there is still no development effort for an MCP suit.  

Here's one more advantage of MCP over a standard full pressure suit.  If you puncture a full pressure suit,  and you cannot get inside before it deflates,  you are dead.  If you puncture an MCP suit,  nothing happens,  because the garment does not contain any gas under pressure at all.  If the hole is smaller than about 0.1 inch in size,  you may ignore it completely,  and just sew it up later.  If it's a bigger tear,  a tight wrap of duct tape will protect the exposed skin from localized vacuum damage until you can go inside and make repairs.  

This MCP suit is the dexterous,  easily-launderable spacesuit we have always dreamed of!  There is simply no excuse not to do this!  So what if it takes some time and effort to don such tight layers?  Further,  if you figure out some scheme to relax and apply the fabric tension “at will”,  even that objection goes away. 

And,  with MCP,  there is zero risk of drowning an astronaut,  because there is no water-cooled underwear!  Astronaut Kopra on the ISS is just the latest to face this lethal risk.  

Related articles on this site:

Date           title

2-15-16    Suits and Atmospheres for Space (the latest!!)

1-15-16   Astronaut Facing Drowning Points Out Need for Better Suit

11-17-14    Space Suit and Habitat Atmospheres

2-11-14      On-Orbit Repair and Assembly Facility
1-21-11     Fundamental Design Criteria for Alternative Space Suit Approaches


1-16-16 two new lead-in paragraphs,  plus rewording of final paragraph,  plus new paragraph 9 about pneumo-thorax.

1-29-16  added information in multiple locations,  red text.