The Space Activity Suit:

An Elastic Leotard for Extravehicular Activity

paul webb, M.D.

 

To provide virtually unrestricted movements in all kinds of extravehicular activities in space, a Space Activity Suit is pro­posed, consisting of a powerful elastic leotard to counter the circulatory effects of breathing oxygen at a pressure of 170 mm.Hg. The physiological basis for such a garment is dis­cussed.

 

A prototype garment has been worn in the laboratory for up to 90 minutes while breathing at pressures of 30, 60, and 100 mm.Hg. Mobility and dexterity were excellent; no circulatory embarrassment appeared. When an arm protected with an elastic gauntlet was exposed to less than 8 mm.Hg absolute for 20 minutes, there was no sign of gaseous swelling, dexterity was unimpeded, and circulation was maintained.

 

A successful Space Activity Suit promises these advantages over gas-filled pressure suits: complete mobility at small metab­olic cost; simplicity and greater reliability; low risk if the gar­ment is torn; and physiological temperature regulation without cooling equipment.

 

THE FULL PRESSURE SUITS used in U.S. and Soviet space flight are enclosures of gastight cloth, pressurized throughout with gas at 0.25 to 0.4 atmos­phere. Physiologically the full pressure suit is correct, but mechanically it is far from satisfactory. Gas bag suits are stiff cylinders except where specific joints or flexible structures are located, and the resulting limited mobility and high metabolic cost of even limited activity while wearing one of these suits cause serious restrictions to extravehicular activity, particularly that which will be needed on the lunar surface.

 

Many kinds of flexible members have been developed in the past thirty years to make such garments some­what mobile, and they have been satisfactory for emer­gency protection in aircraft⁷ or space cabins. But, in contrast, space activities call for all kinds of move­ments. A man on the lunar surface must be able to walk easily, to stoop, to climb, to engage in digging and lifting. These motions involve all the joints and flexures of the body—twisting and flexing of the ver­tebral column from head to pelvis; tilting of the pelvis; rotation, abduction, adduction, flexion, and extension of the arms and legs; and translation of pivot points such as the movable ball-and-socket shoulder joint. To match these complex motions in a gas-filled suit is a formidable job, one which has not yielded to a con­centrated and prolonged effort in research and devel­opment.

 

In order to overcome these problems of awkward­ness, limited mobility, and high metabolic cost—which lead to high oxygen cost, high heat production, and rapid onset of fatigue—a new approach to protection in a vacuum seems to be necessary. For the past two years we have been working on such a new approach. We call it the Space Activity Suit, or SAS.

 

The starting point conceptually for the SAS is that the human skin itself is an ideal pressure suit; the skin is essentially gastight, elastic, and obviously non-re­strictive to motion. The whole body may be exposed to a vacuum for brief periods of one to three minutes without any protection at all, the time limit being set primarily by hypoxia. This has been established by exposures of primates and dogs to a nearly complete vacuum, as reported by Bancroft and Dunn²; Cooke and Bancroft³; Koestler¹²; Rumbaugh and Ternes¹⁶; and Stephens, et al.¹⁷ In the laboratory Wilson²⁰ has exposed human hands to near vacuum conditions (5 mm.Hg absolute pressure), and swelling from evolution of gas was not evident until at least two minutes and often as late as eight to ten minutes after exposure. There are a number of other reports of harmless swell­ing in hands exposed to low pressures—e.g., Ernsting, et al.⁴ Henry, et al.¹⁰ and McGuire.¹³ It would seem that the skin in its natural state exerts a useful degree of elastic counterpressure, and adding mechanical pres­sure will prevent gas from forming.

 

Therefore, in order to provide the added mechanical pressure necessary to protect a man in a vacuum, the Space Activity Suit is constructed of a tough elastic mesh, providing a porous restraint garment conforming entirely to the contours of the body, which supports the skin and prevents it from yielding to the potential distortion of gas forming in the tissues. A helmet sealed to the neck provides oxygen for respiration. The effect of positive pressure breathing on the circulation is compensated by the mechanical counterpressure sup­plied by the elastic net, this requirement in fact calling for more counterpressure than the skin needs for sup­port. At the same time natural thermoregulation takes place by evaporation of sweat without any external cooling equipment, and there should be virtually un­limited mobility at a very small increment in metabolic cost.

 

We have made a prototype SAS and tested it with -positive pressure breathing at ground level. We have also tested subjects' arms in a near-vacuum while protected with an elastic sleeve and glove. In this report we describe the physiological basis for the suit design and present what assurances there are in our testing with early prototypes that the SAS is feasible for use in the vacuum of space. The remarkable ad­vantages of a successful SAS will be evident from the discussion.

HISTORY AND THEORY

 

The idea of using an elastic cloth to provide limb counterpressure during positive pressure breathing is not entirely new. In the early 1940's Henry,⁹ who introduced the partial pressure suit, thought of the elastic suit concept, but did not test it Some time later, Hull,¹¹ at the Aeromedical Laboratories at Wright-Patterson Air Force Base, actually had such a suit constructed, but he didn't pursue the idea further be­cause breathing was uncomfortable and the heavy elastic material then available was stiff and hard to bend.  But positive pressure breathing with limb counterpressure via capstans in the partial pressure suit was eminently successful in providing get-me-down protection when decompression occurred in aircraft. It also provided adequate protection for brief exposures to a near-vacuum.¹³

 

How has the situation changed since the 1940's? The need for unrestricted mobility is far greater for astronauts than for seated pilots in aircraft. In addition there have been impressive postwar developments in fabric technology. Twenty years ago such fibers as spandex, a synthetic elastomer of the polyurethane group, were unknown. Power net and stretch nylon, now standard materials for women's foundation garments, were nonexistent. These fabrics can be knitted or woven in a wide range of powers, from the very lightest used in sheer support stockings to heavy weights used in "full control" girdles and in medical support garments. We are confident that even more powerful fabrics can be developed. By layering these fabrics it will be entirely feasible to produce 150-170 mm.Hg counterpressure over those parts of the body that require it, while maintaining excellent flexibility of parts.

 

The combination of positive pressure breathing and full body elastic counter-pressure affects a number of physiological systems, most importantly the mechanics of respiration, the systemic and pulmonary circulation, and thermoregulation. Each of these functions has been analyzed and an approach has been developed to maintain homeostasis.

Positive Pressure Breathing and Circulatory Balance

 

—Positive pressure breathing (PPB) without compensating counterpressure, and then with counterpressure to the trunk and limbs, has a long developmental history in aircraft protective equipment. Routine use of PPB without compensating pressure is limited to 20-30 mm. Hg for any length of time. With counterpressure on the neck and trunk and partial limb pressurization, as  in the British jerkin, positive breathing pressures of 80 mm. Hg can be tolerated for 10 minutes and 140mm. Hg can be tolerated for one minute, according  to Ernsting.⁵ The partial pressure suits developed by the Air Force in the 1950's use breathing bladders for respiratory compensation and capstans to draw up the non-stretch suit materials over the limbs and trunk; they provide good protection against decompression but the time of use under maximum PPB is limited. And when the bladders and capstans inflate they seriously decrease mobility. The suits are uncomfortable because of uneven pressure distribution and because extensive body coverage by bladders prevents evaporation of sweat. But the greatest drawback has been blood pooling and accumulation of fluid in the limbs when the suits are worn pressurized for longer than 20-30 minutes. The capstan partial pressure suit was never designed for prolonged wear pressurized, or for use by active men in space.

 

For active men in the full vacuum of space, we have chosen 170 mm.Hg (3.3 psi) of oxygen as the design figure for PPB. 150 mm.Hg would approach the sea level partial pressure of oxygen but gives a low alveolar oxygen tension and there would be no safety factor for regulator accuracy, CO₂ flushing, and similar equipment hazards. Since PPB to 170 mm. Hg results in a 170 mm. Hg rise in blood pressure, the blood, being essentially a closed fluid system, is everywhere pressurized to 170 mm. Hg Matching tissue pressure must be created all over the body. The circulating blood would rush into any low pressure areas and pool there; small veins offer almost no resistance to distention. If venous engorgement continued, the pressure within the veins and capil­laries would begin to rise significantly. Once this pres­sure became greater than 14 cm of water gage pressure, measurable amounts of excess fluid would be forced through the capillary walls and would begin to ac­cumulate in the tissues, causing swelling (edema). Neither the blood pooling nor the edema would be markedly uncomfortable, but this sequestering of fluid from the main circulation would result in a decrease in circulating blood volume. Ernsting⁵ has shown that as little as 200 cc lost in this manner, combined with the psychological stresses of PPB, caused fainting, and even the most experienced subjects withstood no more than an 800 cc decrease in circulating blood volume.

 

In order to provide total body counterpressure, ad­justed in magnitude so as to prevent significant pooling or leakage of body fluids, we construct the SAS as a complete leotard of elastic cloth, covering fingers, toes, hands, feet, arms, legs, and torso. We feel from our preliminary studies that the applied force will vary from segment to segment. Probably from 100 to 150 mm.Hg (2-3 psi) of force on the limbs, with up to 170 mm. Hg on the chest and abdomen, will suffice.

 

Special structures under the elastic material are used to fill large concavities and to allow for complex motions where the elastic material does not slide or stretch readily. Such areas are the central back, the axilla, the groin, and the shoulder. In these areas we place shaped soft spongy pads or liquid filled pads which transmit the force of the elastic garment to the skin. At the shoulder, for example, the pad in­vests the whole joint, its liquid normally filling the axillary space. When the shoulder pivot slides over the chest, the fluid redistributes, maintaining a nearly constant volume as the inner geometry is rearranged. These pads, or "soft joints," help to maintain a con­stant pressure over concave areas so that the circulatory balance is not disturbed.

 

Thermoregulation—The third body system that must be maintained is thermoregulation. In the vacuum of space thermoregulation is a problem of heat dissipation. Since an astronaut's heat production will be sizable and variable if he is to cany out useful activities, heat dissipation should be rapidly variable and matched to the requirement of maintaining thermal balance. In the Space Activity Suit, heat dissipation is via the nice­ly regulated mechanism of sweating.

 

The porous net of an SAS permits instantaneous evaporation of any water which comes through the skin. (Overgarments for micrometeorite protection and for control of thermal radiation can be left loose and unsealed, like normal coveralls.) Evaporation cools the skin, heat is dissipated, and sweating decreases.

 

The steady diffusional water loss (insensible pers­piration) in a vacuum should not exceed about 100 grams of water lost per hour per man, an estimate based on extrapolating the data of Hale, et al.⁸ and Webb, et al.¹⁹ This represents a heat loss of 56 kcal/ hr, which is roughly half the metabolic heat produc­tion of a man standing at rest. If there is water pro­duced on the skin from thermal sweating, it will be instantly evaporated and cooling will take place at the rate of 0.56 kcal/gm of water lost. Not only is evap­orative cooling from sweating constantly available and under full control by the body, but also it requires no additional machinery or power. The only limit to this cooling approach is dehydration, and this can be pre­vented by drinking during rest periods. If the astro­naut's work rate were maintained at a steady 300 kcal/hr (1200 Btu/hr) for four hours, the total loss of water would be just over 2100 grams for the whole period. It all evaporates and cools; there is no need for the body to secrete 1.5 to 2 times the sweat re­quired for cooling, as is often true in an air environ­ment on Earth.

 

 

Fig. 1. The high heat production (metabolic cost) of walk­ing slowly in pressurized full pressure suits, from data of Wortz et al²¹ and Roth,¹⁵ compared to the normal heat production of walking at common speeds without encumbrance (data of Alt-man, et al¹).

 

Properties of Human Skin—The tensile strength of human skin is more than adequate to prevent serious deformation or rupture in the small spaces between the strands of elastic netting. According to Yoshi-mura,²² the average tension required to tear adult human skin is 1600 gms/mm², while the maximum force of 170 mm. Hg which might be developed wearing the SAS is 2.3 gms/mm.² The elastic materials we are now using show spaces as big as 1 mm² only when grossly overstretched

The skin as a barrier to gaseous diffusion has been studied enough to permit educated guesses as how much water vapor, oxygen, nitrogen, and carbon dioxide would be lost during exposure to a vacuum. Our estimate of the rate of diffusion of water vapor was given in the preceding section—about 100 gms per hour. This may well be too generous, since the barrier layer of the skin increases its resistance to diffusion as the skin becomes drier, and the immediate effect of exposure to vacuum will be maximal drying of the superficial horny layer.

 

Moyer, et al.¹⁴ feel that the skin remains gastight when the transcutaneous pressure exceeds 760 mm.Hg. Diffusion of individual gases through the skin has   been reported by Fitzgerald⁶ as negligible for oxygen and about 180 ml(STPD)/hr for CO₂ when there is no transcutaneous pressure gradient. Dissolved nitrogen will be at a low value from the standard procedure of breathing oxygen before going into the vacuum environment. We estimate the nitrogen diffusion through the skin may be 10-20 ml/hr.

 

All of these estimates of gaseous diffusion rates may have to be revised when experimental measurements can be made during exposures to full vacuum. How-ever, on the basis of present information, we do not expect any problem from excessively high loss by transcutaneous diffusion.

 

Other Features— Reliability of the SAS is high due to its drastic simplification compared to full pressure suits. There are far fewer parts to fail, as witness the elimination of cooling equipment and the absence of mechanical joints. The backpack is simplified to a package containing only oxygen for breathing. Safety is enhanced, since a tear in the tough elastic material would not represent the catastrophe that a tear in a gas-filled suit means. The complete suit (except for the outer coverall) will be small enough to tuck into the interior of the helmet for storage.

 

But it must be kept in mind that the first and major advantage of the Space Activity Suit is that it gives total flexibility for all body parts. Since mobility essentially unimpeded, the incremental energy cost of doing useful activities in the SAS should be small Total mobility allows use of all the familiar actions of body parts in carrying out a task—not the constrained and unfamiliar motions used when "walking," for example, in a full pressure suit. The bending forces in the elastic net are greater than those for normal clothing, but these forces are expected to be small compared to the forces the muscles normally generate when a man walks, climbs, stoops, digs, and weights. We estimate that the metabolic cost of carrying out a full schedule of walking and climbing activities will not increase by more than 10 to 20 percent in the SAS.

 

In contrast, the data for operating in standard pressure  garment assemblies show extreme incremental increased  with even mild activity. Some typical energy cost values for walking at very slow speeds in pressure suits at 1 g are given in Figure 1. Increases of three times the cost of walking unpressurized are not unusual. When we compare this metabolic cost with the anticipated 10 to 20 percent increment of the SAS, and when we recognize that many simple activities are virtually impossible to do in conventional pressure suits, the advantages of the SAS are compelling.

PROTOTYPE TESTING

In order to demonstrate the mobility inherent in the SAS concept and to study the effects of prolonged PPB with elastic counterpressure, we have made an elastic  leotard of several layers so that increasing power is applied as layers are added. Initial demonstrations of mobility, dexterity, and lack of circulatory effects have been carried out with this prototype garment. In ad­dition we have exposed the arm and hand of two sub­jects protected with a double elastic sleeve to a near-vacuum in an arm chamber, with no swelling and no harmful effects.

 

First Prototype Garment—The first prototype gar­ment was carefully tailored to the individual measure­ments of one subject. The power applied by donning each layer of this garment was accurately calculated and achieved by the techniques developed by the Jobst Institute of Toledo, Ohio, a supplier of medical sup­port garments. The material used was a special bobbinet woven with cotton-covered 50-core rubber strands in the warp direction running circumferentially around  the limb and 100-denier nylon in fill. The material has two-way stretch but the main power is developed circumferentially in the direction of the rubber strands. Three layers were made, each consisting of a pair of garments, one member of which ran from the foot to the shoulders, without arms, and the other member from the crotch to the base of the fingers, without legs. Each pair when donned provided single coverage on the arms and legs and double coverage on the trunk. Elastic gloves and footlets completed the assembly. The first two pairs- of garments developed powers of 30 mm.Hg and the third pair developed a power of 40 mm.Hg. The applied mechanical pressure of each layer was checked and verified to be 30, 30, and 40 respectively, and the combination gave approximately 100 mm.Hg by our technique of measurement.

 

Measuring the applied power was accomplished with small flat inflatable pads fitted with two electrical leads and a small pneumatic connection. The flat pads, or  envelopes, were made of 10-gage vinyl sheet and were cut in a roughly oval shape measuring approximately 1 X ¾ inches. The inside surfaces of the two layers were fitted with thin electrical contacts. Inflation with a syringe through the pneumatic connector caused the contacts to separate. When the pads were placed under the elastic material and against the skin, the pressure required to break the contacts was our index of the force applied by the elastic garment.

 

The suit was always worn in the laboratory with positive pressure breathing delivered by a helmet which was connected to a simple flow-through com­pressed air supply. The helmet sealed around the face and supplied pressure to the neck and most of the head by means of a bladder. The suit and helmet are seen as worn in Figure 2.

 

A single layer of the prototype garment developing 30 mm.Hg was worn with 30 mm.Hg PPB for 90 min­utes with complete comfort. Two layers of the proto­type garment, which together develop 60 mm.Hg pres­sure, have been worn twice; the first period was 90 minutes and the second 45 minutes. During the first and longer trial, the subject complained of fatigue of the abdominal muscles from unusual respiratory ef­fort. A double-layered elastic corset was added to the lower torso to aid in respiration and this relieved the discomfort. Three layers were worn together to de­velop a pressure of approximately 100 mm.Hg for 10 minutes.

 

Mobility and dexterity—While it was evident to the subject and to the observers that there was excellent mobility in the first prototype garment with either one, two, or three layers, we devised a simple set of body motions to demonstrate that there was good flexibility. Since the subjects in current full pressure suits have difficulty in keeping up with a treadmill, and greater difficulty in stooping, climbing, and other activities in­volving trunk flexion, we asked our subject to do the following things, which he did happily for a period of about 45 minutes. First, on the treadmill, the sub­ject walked at 3 mph on a level, then at 3 mph up a 5 percent grade, then at 3 mph level with a 30-lb. backpack, and then at 4 mph with a 25 percent grade with the backpack. This last heavy exercise was main­tained for 30 seconds without great difficulty. The subject donned and buckled his own backpack. Next the subject was asked to do a number of calisthenic

 

Fig. 2. Subject wearing 30 mm.Hg suit with 30 mm.Hg breathing pressure via air line being attached to helmet.

 

To demonstrate hand dexterity we asked the subject activities including sit-ups, push-ups, trunk bends in all directions, squat jumps; knee bends, and toe touch­ing. Again these were accomplished without difficulty. Finally, he was asked to shovel sand from one con­tainer to another using a long-handled shovel; he was asked to climb a 14-foot ladder, up and down several times; and he was asked to crawl on the treadmill at 1.2 mph both level and up a grade. All of these ac­tivities were carried out without difficulty. There was no excessive increase in heart rate nor excessive respira­tory distress.

 

While direct metabolic data were not taken, it was clear that the metabolic cost of doing these activities, some of which are virtually impossible in a full pressure suit, was only a little greater than would be measured if he had had no suit on at all. Figures 3, 4, and 5 are photographs of the subject doing some of the activities described.

 

Fig. 3. Lateral trunk flexion in the 60 mm.Hg assembly.

 

to write on a tablet, to fasten and unfasten Swagelok connectors and other small items of hardware and to operate the controls of an oscilloscope, electronic amplifiers, and similar laboratory instrument None of these requests caused any great problem al-though the cloth of the gloves reduced his tactile sense, as would any cloth glove of equal weight. There was no striking diminution of dexterity because of the elastic garment.

 

These simple tests of mobility and dexterity are sufficient to show that the SAS is qualitatively different from full pressure suits and partial pressure suits.

 

Circulatory Effects—Positive pressure breathing was adjusted to match the applied elastic counterpressure of the prototype garments, namely 30 mm.Hg with a, single layer, 60 mm.Hg with two layers, and 100 mm.Hg with the three layer assembly. In the four different wearing trials the subject was usually quite active. However, in one portion of the 90-minute trial at 60 mm.Hg pressure, the subject was purposely kept still in a vertical position to see whether blood pooling was a specific problem. For 15 minutes the subject leaned against the ladder at an angle of 70° from horizontal, and he was asked to relax and remain as quiet as possible. This was intended to be an exaggerated duplication of the conditions leading to parade ground faint. There was no noticeable change in pulse rate; the subject felt perfectly well and the blood pres­sure measurements did not change during this period.

 

Blood pressure measurements showed that the ar­terial pressure increased in the amount that positive pressure breathing was applied. Our subject normally had a standing resting arterial pressure of 130/85. With one suit layer and 30 mm.Hg of PPB the read­ing was 170/125. With 60 mm.Hg positive pressure and a 60 mm. garment assembly, his standing resting pressure was 180/150. With 100 mm.Hg PPB and elastic pressure applied, his standing resting pressure was 230/180.

 

                                   

Fig. 4. Climbing an extension ladder in the 60 mm.Hg as­sembly.           

Fig. 5. Crawling on the treadmill at 1.2 mph in the 60 mm.Hg assembly.

 

There was no functional evidence, then, of circulatory imbalance. Inspection revealed no evidence of edema in the hands or feet. The subject had no immediate or late effects from the wearing trials.

 

We had expected to see some edema or evidence of circulatory embarrassment locally in concavities and joint areas like the axilla. We had used padding and fills only in the inguinal region and the center of the back. No edema appeared. Neither was there any evidence of restriction of joint motion at the shoulder even though we did not use a liquid filled bag with this prototype garment.

ARM EXPOSURES TO NEAR-VACUUM

 

Preliminary studies have been carried out with sup­port from the Langley Research Center, NASA, to demonstrate the ability of the elastic material to pre­vent gaseous swelling under the skin.¹⁸

 

After studying various elastic knitted and woven materials in order to find one with sufficient power to increase the pressure of the arm tissue by approxi­mately 100 mm.Hg, and after testing the materials in a vacuum dessicator jar to make sure that they did not lose their elasticity in a vacuum, we choose the bobbinet material described previously.

 

After carefully measuring the arms and hands of two experimental subjects, we had made a full-arm gauntlet plus an oversleeve without fingers for each of the subjects. The two sleeves together developed approximately 100 mm.Hg counterpressure by compu­tation. We explored the "soft joint" concept in a pre­liminary way, but when we found that elbow and wrist joints did not need any aid to full mobility, we did not use soft joints in those parts. We did, how­ever, mold silicone rubber pads to fit the palm and back of the hand for each subject in order to round out those surfaces and to reduce the strong elastic force on the edges of the hand.

 

In order to simulate conditions of space for only one part of the body, we constructed a vacuum cham­ber into which the arm could be sealed. We made this chamber of ½" Lucite in the shape of a cylinder 18" in diameter and 36" long. The arm chamber was fitted out in the interior with a number of electrical switches, knobs, and colored lights, as shown in Fig­ure 6. The subject tested mobility and flexibility of his arm in the protective sleeve by manipulating these knobs and switches.

 

We conducted tests in an altitude chamber where total pressure was reduced to 155 mm.Hg (equivalent to 38,000 ft). By evacuating the arm chamber, the differential pressure was 150 mm.Hg, and the arm itself was exposed to near-vacuum conditions, or 5-8 mm.Hg total pressure. Pressure profiles of two of these experiments are shown in Figure 7.

 

The results of the tests were encouraging. The hand and arm remained perfectly flexible and dex­terous, did not show gas formation in the tissues, and apparently had adequate circulation for 20 minutes There was no apparent increase in the metabolic cost of doing arm and hand movements while wearing the sleeve. The circulation seemed to be in balance; there was arterial inflow and venous outflow in the axilla, as measured by a Doptone ultrasonic blood flowmeter (Smith Kline Instrument Co.). There was no ischemic pain or skin damage, and arm volume had not changed significantly after the test.

 

We tested again, at ground level, to see if higher differential pressures with the same sleeve were tol­erable. When negative pressures of 150 mm.Hg and 200 mm.Hg were tried with the same 100 mm.Hg sleeve, fluid accumulated in the arm, as evidenced by increases in arm volume of 5 and 8 percent respec­tively following the 20-minute exposure. Some of this fluid leakage probably resulted from a tourniquet ef­fect at the point where the arm sealed to the arm chamber, and some resulted from blockage of venous return due to the imbalances between negative pres­sure and applied counterpressure. Except for a full or tight feeling, there was no subjective discomfort, and the swelling was gone in 8-10 hours.

 

Fig. 6. The Lucite arm chamber with beveled armhole in the near end. Internal switches and lights are visible on the floor and walls. Scale in inches.

 

Fig. 7. Pressure profiles of two experiments in the altitude chamber with the protected arm at near-vacuum conditions in the arm chamber.

SOME PROBLEMS

There are bound to be problems ahead. Some of the problems which worried us originally have re-solved themselves in trying the first laboratory prototypes; for example, most small concavities do not need filling. Looking far ahead to possible operation from a spacecraft, we are concerned about several things.

 

Donning the powerful elastic leotard may be a real problem unless some clever solutions are found. The present multi-layered assembly, with strategically placed zippers in the legs and torso, is manageable, and can be donned unassisted, with practice, in about 10 minutes. To achieve the full counterpressure needed for PPB at 170 mm.Hg we may have to use several layers of a more powerful fabric, and the more power per layer the harder it is to pull the garment on. Donning aids may be necessary, and they must be devised. Special tensioning devices may also be help­ful, e.g. speed lacings pulled tight after the garment is on. Another solution would be to include blind gas-filled bladders under the elastic material which would ex­pand when the astronaut leaves the spacecraft, there­by increasing the tension of the garment. This would represent something of a compromise to the original SAS principle, and we shall probably stay with elastic materials for the present to see if the pure form of an SAS will be workable.

 

As we develop suits with higher elastic power, we may lose some of the flexibility of the first SAS proto­types. The more layers, the stiffer the garment feels. But elastic fabrics with spandex yarns are significantly lighter than rubber core fabrics of equal power. We should be able to achieve the necessary elastic counter-pressure with fewer layers or lighter fabric.

 

Some elastic fibers lose their elasticity on prolonged exposure to a hard vacuum. Our preliminary testing, and information we have from manufacturers, are en­couraging. One of the spandex yarns particularly has shown excellent resistance both to vacuum and to ultra-violet radiation.

 

Finally, there are serious potential problems in the smooth application of adequate elastic counterpressure to all parts of the body. We have already learned that some concavities, like the trough over the lumbo-dorsal spines, need to be filled. It is difficult to apply the elastic material in the axilla and over the scrotum. So far, the tight fit of the prototype garment and pad­ding over the inguinal and femoral canals seems to have been adequate; we have not seen edema or evi­dence of venous obstruction in the axillae. More work will be needed with liquid-filled bags and with open-cell foams. But beyond these problems with special body sites, we cannot be certain at this stage that we can adequately compensate for the circulatory imbal­ances caused by prolonged breathing at high positive pressure. We are encouraged by our preliminary ex­periments, but we realize that at even higher breathing pressures the problem will increase. The pooling of blood, with loss of circulating blood volume, has not been easy to prevent in partial pressure suits, and this is critical. Our hope is that new elastic   materials and carefully engineered tailoring will provide the solution.

CONCLUSIONS

The concept of positive pressure breathing at 170 mm.Hg with full body counterpressure from an elastic leotard appears to be feasible and physiologically sound. This garment should adequately protect an active man in a vacuum.

 

Mobility and dexterity are virtually unhampered in the first prototype garments, and many extravehicular activities which are either difficult or impossible in full pressure suits should be easy to manage in the Space Activity Suit.

 

Assuming the satisfactory resolution of the problems already foreseen, the Space Activity Suit promises major additional advantages in simplicity, reliability, reduced accessory equipment, and safety.

ACKNOWLEDGMENTS

The work described in the section "Arm Exposures to a Near-Vacuum" was accomplished under the terms of contract NAS1-6872 with the Langley Research Center, National Aeronautics and Space Administration.

 

James Annis and Jerome Westin, M.D., gave generously of their energies and skill in the laboratory studies. Altitude chamber studies were conducted in the facilities of the Aero-medical Research Laboratory, Department of Preventive Medicine, the Ohio State University.

 

A major contribution was made by the Jobst Institute, Toledo, Ohio, whose competence in the application of biomechanicial pressure and whose enthusiasm for the project were ingredients in fashioning the prototype garments.

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