This is a concept proposal for a better version of the
mechanical counter-pressure (MCP) space suit.
It combines the best features and eliminates the worst disadvantages of
the particular two MCP design approaches upon which it is based. These are the “partial pressure” suit of the
1950’s and the “elastic space leotard” of Dr. Paul Webb. The result should be a lightweight, supple (non-restrictive) suit that with
suitable unpressurized outerwear, can be
used on pretty much any planetary surface even if totally airless, or even in space. It need not use exotically-tailored
materials in its construction.
It should be relatively easy to doff and don.
This article updates earlier articles on this subject.
Those are:
Date title
2-15-16 Suits and
Atmospheres for Space (supersedes those
following)
1-15-16 Astronaut Facing Drowning Points
Out Need for Better Space 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
The idea here is to combine the two demonstrated approaches
that both apply the fundamental MCP principle:
the body needs pressure applied to its skin to counterbalance the
necessary breathing gas pressure. The
body simply does not care whether this counter-pressure is applied as gas
pressure inside a gas balloon suit, or is
exerted upon the skin by mechanical means.
The first article cited in the list above (“Suits and
Atmospheres for Space” dated 2-15-16) determines that pure oxygen breathing gas
pressures from 0.18 atm to 0.25+ atm should be feasible. How that was calculated is not repeated
here. My preferred range of helmet
oxygen pressures is 0.18 to 0.20 atm,
for which wet in-lung oxygen partial pressures range from 0.11 to 0.13 atm, same as the wet in-lung oxygen partial
pressures in Earth’s atmosphere at altitudes between 10,000 and 14,000
feet.
However, only 0.26
atm gives you the same wet in-lung oxygen pressure as sea level Earth air. The 0.33 atm used by NASA is entirely unnecessary, unless to help overcome the exhaustive efforts
necessary to move or perform tasks, in
the extremely stiff and resistive,
heavy, and bulky “gas balloon”
suits they use.
The 1940’s design that operationally met the need for
extreme altitude protection for short periods of time was the “partial
pressure” suit of Figure 1, in which compression
was achieved with inflated “capstan tubes”.
These suits were widely used into the 1960’s. The capstans pulled the non-stretchable
fabric tight upon the torso and extremities.
This provided the counterpressure necessary for pressure-breathing
oxygen during exposures to vacuum or near vacuum, for durations up to about 10 minutes
long. This was for bailouts from above
70,000 feet, and would have worked for
similar short periods even in hard vacuum.
Hands and feet were left uncompressed,
but for only 10 minutes’ exposure,
these body parts could not begin to swell from vacuum effects.
The advantages of this design were (1) ease of doff and
don, (2) it was simple enough to be
quite reliable, and (3) it was not very
restrictive, whether the capstan tubes
were pressurized or not. The
disadvantages were the achievement of rather-uneven compression, and leaving the hands and feet completely uncompressed. This limited the allowable exposure time by
(1) uncompressed small body parts begin swelling in about 30 minutes, and (2) between the uncompressed parts and
the uneven compression achieved on the extremities, blood pooling into the under-compressed parts
could lead to fainting within about 10 to 15 minutes.
Figure 1 – Partial Pressure Suit Design Used From the late 1940’s to the Early 1960’s
In the late 1960’s,
Dr. Paul Webb performed striking experiments with an alternative way to
achieve mechanical counterpressure upon the body. He used multiple layers of elastic fabric
(the then-new panty hose material) as a tight-fitting leotard-like
garment. This was not a single-piece
garment. It achieved more-uniform
compression on the torso and extremities than did the older partial pressure
suit. Dr. Webb included elastic
compression gloves and booties, so that
the entire body was compressed, removing
the time limits. Breathing difficulties
were solved with a tidal volume breathing bag enclosed by an inelastic
jacket.
Breathing gas was pure oxygen at 190 mm Hg pressure (0.25
atm) fed into the helmet from a small backpack with a liquid oxygen Dewar for
makeup oxygen. This type of garment was very
unrestrictive of movement, and was
demonstrated quite adequate for near-vacuum exposures equivalent to 87,000 feet,
for durations up to 30 minutes. It was intended for possible application as
an Apollo moon suit, but could not be
made operationally ready in time. It has
been mostly forgotten ever since.
The advantages are very unrestricted movement, very light weight (85 pounds for suit plus
helmet plus oxygen backpack), and no
need for a cooling system: you just
sweat right through the porous garment,
same as ordinary street clothing.
Plus, the garment’s pieces were
quite launderable. Dr. Webb’s test rig
is shown in Figure 2. 6 or 7 layers of
the panty hose material provided adequate counter-pressure.
Figure 2 – Dr. Webb’s “Elastic Leotard” MCP Space Suit Prototype as Demonstrated
The disadvantages were essentially just difficult (time-consuming)
efforts to don and to doff the garment’s pieces, precisely because they were inherently very
tight-fitting. For use on a
planetary surface or out in space, one
treats the suit as “vacuum-protective underwear”, and adds insulating or otherwise protective non-pressurized
outerwear over it. So protection from
hazards is not a disadvantage at all, but
only if one uses the vacuum-protective underwear notion.
The main advantage of Dr. Webb’s “elastic space leotard”
over the “partial pressure” suit was the more even (and more complete)
compression achievable with the elastic fabrics. The main advantage of the “partial pressure”
suit over the “elastic space leotard” was the ease of donning and doffing the
garment, when the capstan tubes were
depressurized, releasing the fabric
tension. Both approaches offer very
significant advantages over the “gas balloon” suits in use since the 1960’s as
space suits: lighter, launderable,
and far, far more supple and
non-restrictive for the wearer.
That suggests combining both of the successful MCP design approaches (inflated
capstans and elastic fabrics) into a single mechanical counterpressure suit
design. The capstans apply and
relax the tension in the fabric which provides the counter-pressure on the body, and the elastic fabric makes the achievable
compression far more uniform. What is
required from a development standpoint is experimental determination of the
number of layers of elastic fabric required for each piece of the garment, in order to achieve the desired compression in
every piece.
If done this way,
there is no need for directionally-tailored stiffness properties in
specialty fabrics, the basis of Dr. Dava
Newman’s work with mechanical compression suits (see Figure 3). Ordinary commercial elastic fabrics and
ordinary commercial joining techniques can be used. In other words, pretty much anyone can build one of these
space suits!
Figure 3 – Dr. Dava Newman’s MCP Suit Based on
Directionally-Tailored Fabric Properties
So, the MCP suit proposed
here has certain key features (see list below).
It will resemble the old “partial pressure” suits, except that protective outerwear (insulated
coveralls, etc.) get worn over the compression
suit itself, and the helmet is likely a
clear bubble for visibility. There is an
oxygen backpack with a radio. There is
no need for any sort of cooling system.
Everything is easily cleaned or laundered free of dust, dirt, sweat, and similar contamination.
Key features list:
#1. Pressurized capstan tubes pull the elastic fabric tight
whenever the helmet oxygen is “on”, but
depressurize and slack the garment tension when helmet oxygen is “off”. The capstan tubes are just part of the oxygen
pressure breathing system. Slacking the
fabric tension makes doff and don far easier.
#2. The multi-piece garment is composed of multiple layers
of elastic fabric to provide the desired level of stiffness that will achieve
the desired level of compression in each piece of the garment. This depends upon both the shape of the
piece, and upon how much circumferential
shortening is achieved by inflating the capstan.
#3. The pressure garment is vacuum-protective
underwear, over which whatever
protective outerwear garments are worn that are appropriate to the task at
hand. For example, the wearer might need white insulated
coveralls and insulated hiking boots,
plus insulated gloves. One could
even add some sort of simple broad-brimmed hat to the helmet if sunlight were
intense.
#4. The clear bubble helmet is attached to the torso garment
piece. This torso garment piece also incorporates an inelastic jacket
surrounding a tidal volume breathing bag.
Helmet, breathing bag, and capstans all pressurize with oxygen from
the supply simultaneously, and are (in
fact) connected. All are activated by
one on/off control.
#5. The oxygen
backpack is just that, no cooling system
required. It probably uses liquid oxygen
from a Dewar as make-up oxygen, has
regeneratable carbon dioxide absorption canisters, and a battery-powered radio. It might also contain a drinking water feed
connected to the helmet. Attitude and
translation thrusters for free flight in space can be a separate chair-like
unit, and this function is entirely unnecessary
on a planetary surface.
#6. For concave body surfaces and complex shapes like
genitalia, the pressure suit can
incorporate semi-fluid gel packs that surround these body parts, making the body effectively convex
everywhere.
Figure 4 – How the Capstans and Elastic Fabric Work Together
for an Improved MCP Suit
About the only caveat might be that the breathing gas pressure could
be too small to also serve as the capstan inflation pressure. If that should prove to be true, then there need to be two final pressure
regulators in the oxygen backpack,
instead of just one. That problem
can be easily solved!
