Significant Achievements in Space Bioscience 1958-1964 Part 10

THE NASA BIOSATELLITE PROGRAM

From [ref.169].

The s.p.a.ce environment offers a unique opportunity to study the basic properties of living Earth organisms with new tools and opens up new areas of research for which biological theory fails to provide adequate predictions. Unique components of the s.p.a.ce environment of biological importance are weightlessness or greatly decreased gravity, the imposition of an environment disconnected from Earth's 24-hour rotation (particularly its effect on biorhythms), and cosmic radiation with energies and particle sizes unmatched by anything produced artificially on Earth ([ref.169]).

As progress is made in the manned exploration of s.p.a.ce, the biological effects of its unique environmental factors become of greater importance. It is essential to determine the effects of s.p.a.ce environment on man's ability to perform physical and mental tasks. In addition, it is necessary to develop those systems required for his survival and for his physiological and psychological well-being, both in s.p.a.ce and in his subsequent resumption of normal life patterns. Despite nearly a century of research and development in environmental physiology, a number of phenomena will be encountered in long-term s.p.a.ce flight with which we have had neither the experience that would enable us to predict the effects nor to develop the necessary protective or remedial measures ([ref.170]). Many of the experimental programs in bioscience are being carried out or planned so that the deleterious effects of these phenomena may be determined, predicted, or avoided before they are encountered in manned flight.

Biological experimentation has been carried out in orbiting s.p.a.cecraft by Soviet and American scientists preparatory to manned s.p.a.ce flight.

These first-generation exploratory experiments had the following objectives:

(1) To discover whether complex organisms could survive s.p.a.ce conditions and to test life-support systems (2) To determine whether complex organisms (dogs and primates) could survive launch, orbital s.p.a.ce flight, reentry, and recovery (3) To determine the effects of s.p.a.ce radiation and any obvious effects of weightlessness on biological organisms

These biological studies indicate that manned s.p.a.ce flight was practicable, and the various cosmonaut and astronaut flights have proven the validity of the results.

The National Academy of Sciences' s.p.a.ce Science Board summer study ([ref.171]) recommended that-

NASA should exploit special features of the s.p.a.ce environment as unique situations for the general a.n.a.lysis of the organism-environment relations.h.i.+ps including, especially, the role environmental inputs play in the establishment and maintenance of normal organization in the living system. NASA should support studies in ground-based and in orbiting laboratories [biosatellites] on the biological effects of gravity fields both above and below normal. This should be considered a major responsibility of NASA in the area of environmental opportunities. NASA should support studies of biological rhythms in plants and animals including man as part of its effort in environmental biology. Investigate by observation of rhythms in organisms in s.p.a.ce in (_a_) polar and equatorial low orbits; (_b_) orbits less than, equal to and greater than 22,000 miles. Properly designed experiments should be conducted to explore the effects of different environmental factors when these impinge simultaneously on test organisms.

The Panel on Gravity of the s.p.a.ce Science Board ([ref.67]) stated that the major effects of low gravity would be expected in heterocellular organisms that develop in more or less fixed orientation with respect to terrestrial gravity and which respond to changes in orientation with relatively long induction periods, including the higher plants. On the other extreme are the complex primates which respond rapidly, but whose multiplicity of organs and correlative mechanisms make the occurrence of malfunction and disorganization probable, but not certain. The Panel recommended emphasis on early embryogenesis and histogenesis, particularly of plants during exposure to low gravity, and anatomical studies after low gravity. They stated that perturbations of the environment to which the experimental organism is exposed must be limited or controlled to reduce uncertainties in interpretation of results. At the same time, the introduction of known perturbations may a.s.sist in isolating the effects due solely to gravity. Ground-based clinostats and centrifuges should be used in conjunction with the experiments, and an attempt should be made to extrapolate effects of low gravity with the clinostat.

The study of the effects of unique or unknown s.p.a.ce environmental factors will probably yield unexpected results which may drastically modify future technical approaches. The results from these biosatellite studies will have broad application to longer term, manned s.p.a.ce flight, including manned s.p.a.ce stations and lunar and planetary exploration.

The biosatellite program is a second-generation series of carefully planned and selected experiments, including some highly sophisticated experiments which have required several years of baseline study and equipment development. These orbiting recoverable biosatellites will provide opportunities for critical testing of major biological hypotheses in the areas of genetics, evolution, and physiology.

The scientific community showed great interest in the biosatellite program, and scientists from universities, industry, and Government have submitted 185 flight experiments involving primates and other mammals, vertebrate and invertebrate animals, micro-organisms, and plants.

The selected biosatellite experiments include studies at the cellular, tissue, and organism levels, including embryological development and growth experiments at the tissue level and physiological, behavioral, reproductive, and genetic studies at the organism level. The experiments are divided into six categories:

(1) Primates (2) Mammals (nonprimate) (3) Animal, cellular, and egg (4) Plant morphogenesis, photosynthesis, and growth (5) Biorhythm (6) Radiation

Twenty experiments have been selected for flight to study the effects of weightlessness and decreased gravity during 3- to 30-day orbital periods. The experiments include a wide variety of plants and animals from single-celled organisms to higher plants and animals. The effects of weightlessness on the primate will be studied, especially the central nervous, the cardiovascular, and the skeletal systems during 30-day orbits.

Experiments have been selected to study the genetic and somatic effects of weightlessness combined with a known source of radiation (Sr85) to determine if there are any antagonistic or synergistic effects ([ref.172]). Experiments are also included for studying the effects of the unique environment of the Earth-orbiting satellite and removal from the Earth's rotation in relation to biological rhythms of plants and animals.

Six biosatellites are included in the presently approved program, with the first flight in 1966. They will be launched from Cape Kennedy by the improved two-stage, thrust-augmented Thor-Delta into a nearly equatorial circular orbit at an alt.i.tude of 180-200 miles for periods up to 30 days. Recovery will be by Air Force airplane during capsule/parachute descent. The s.p.a.cecraft weigh 1000-1200 pounds, have a 280-pound recoverable capsule and, while in orbit, will not experience greater than 1/10 000 g of acceleration. The life-support system will provide an environment at sea-level pressure of 80 percent nitrogen, 20 percent oxygen, and no more than 0.5 percent carbon dioxide with a temperature of 75 F 5 F.

All experiments are in various stages of development or testing and flight test hardware has been and is being constructed. The experiments and hardware are being subjected to preflight tests simulating launch and recovery stresses. Rhesus, pigtail, and squirrel monkeys have been subjected to the dynamic forces of the simulated flight under conditions of complete, partial, and no restraint. Three types of centrifuges have been used to simulate the flight profile. Primates were fully instrumented with deep brain electrode implants, implanted catheters, and other implanted sensors. During centrifugation, motion pictures were taken. These primates were semirestrained in form-fitted couches which allowed movement of the body while facing the accelerative force in a ventrodorsal position (eyeb.a.l.l.s in). In this series of tests, all primates were normal following the tests and exhibited no unusual behavior or effects. X-rays showed that implanted catheters and electrodes remained in place, and there were no movements causing tissue damage. However, when the primates were placed with their backs toward the accelerative force, dorsoventral (eyeb.a.l.l.s out), the animals suffered visible damage. At 6 g there was no visible stress, but at 8 g swelling of the lower eyelids was noticeable. At 11 g both eyelids were swollen shut. In the biosatellite program, primates will be placed in the semirestraint couches in a position facing accelerative forces, ventrodorsal (eyeb.a.l.l.s in), to prevent these effects.

chapter 7

_Manned s.p.a.ce Flight_

BIOREGENERATIVE LIFE-SUPPORT SYSTEMS

Placing a man in s.p.a.ce requires a complete life-support system capable of supplying sufficient oxygen, food, and water and removing excess carbon dioxide, water vapor, and human body wastes. In addition, the oxygen, carbon dioxide, and pressure must be maintained at a suitable level. Any acc.u.mulated toxic products and noxious odors must be removed.

In the s.p.a.cecraft the human is confined in a restricted environment in which it is necessary to establish a balanced microcosm or closed ecological system. This is an enormous biological and bioengineering problem. Weight, size, simplicity of operation, and reliability particularly are important factors.

For relatively short missions involving one or several astronauts, food, oxygen, and water can be stored and made available as required, and the various waste products can be stored. On longer missions, particularly those involving more than one astronaut, efficient chemical or biological regenerative systems will be required. Any regenerative system introduces a fixed cost in weight of processing equipment and energy requirements.

Chemical, or partially regenerative, methods for providing breathing oxygen by the regeneration of metabolic products such as water vapor and carbon dioxide include the thermal decomposition of water and CO2, photolysis and radiolysis of water, electrolysis of fused carbonates and aqueous solutions, and the chemical reduction of CO2 with H2, followed by electrolysis of the water formed. Chemical regenerative systems have been developed to remove excess carbon dioxide and water vapor from the atmosphere. Nonbiological regenerative systems are time limited by the amount of food, water, and oxygen that can be carried or recovered.

These physical-chemical processes show great potential, but they also present many difficulties, including requirements for extremely high temperatures and considerable amounts of power, the formation of highly toxic materials, and high susceptibility to inactivation. None of the presently studied nonbiological processes can function as completely as a bioregenerative system. All these nonbiological systems have unrealistic supply requirements and produce unusable wastes.

Consequently, for long planetary missions the bioregenerative systems, though also beset with problems, are potentially far superior to their physical and chemical counterparts.

Table VIII shows average daily metabolic data for a 70-kg astronaut. A man breathes about 10 cubic feet of air per minute, or 400 000 liters, daily. The expired air contains about 4 percent carbon dioxide. Man normally breathes air containing 0.03 percent CO2, but can withstand comfortably about 1.5 percent CO2. Anything in excess of 1.5 percent will produce labored breathing, headaches, and, if greatly exceeded, death. A man exhales about 1.1 pounds of water per day and this, in addition to water from perspiration and other sources, must be removed from the air.

Table VIII.-_Average Daily Metabolic Data for a 70-kg, 25-Year-Old Astronaut With Normal s.p.a.cecrew Activity_ [From [ref.173]]

----------------------------------------------------------------- O2 input, kg 0.862 ----------------------------------------------------------------- CO2 output, kg 1.056 ----------------------------------------------------------------- Drinking water, liters 2.5 ----------------------------------------------------------------- Food rehydrating water, liters 1 ----------------------------------------------------------------- Caloric value of food, kcal 3000 ----------------------------------------------------------------- Water output: ----------------------------------------------------------------- Urine, liters 1.6 ----------------------------------------------------------------- Respiration and perspiration, liters 2.13 ----------------------------------------------------------------- Feces, kg 0.09 ----------------------------------------------------------------- Total heat output, Btu 11 100 -----------------------------------------------------------------

Two types of biological regenerative systems have been proposed. The photosynthetic closed ecological system was proposed as early as 1951.

This involves the use of single-celled algae or higher plants, including floating aquatic and terrestrial plants, and requires the interaction of light energy with CO2 and H2O to produce O2 and plant cells. Another system, proposed in 1961, involves electrolysis of water into oxygen and hydrogen, and the concurrent use of _Hydrogenomonas_ bacteria which take up hydrogen, some oxygen, carbon dioxide, and urine yielding water and bacterial cells.

Table IX.-_Requirements for Regenerative Life-Support Systems_ --------------------------------------------------------------------- Requirements / Requirements / 1 man4 3 men (270 man-day System mission)5 --------------------------------------- Weight, Power, Weight, Power, kg kW kg kW --------------------------------------------------------------------- Partial chemoregenerative 7 332 1.75 --------------------------------------------------------------------- LiOH 125 1.40 --------------------------------------------------------------------- NaOH 155 7.68 --------------------------------------------------------------------- CO2-H2 34 .36 --------------------------------------------------------------------- Full bioregenerative-algae: --------------------------------------------------------------------- Artificial illumination 116 6 10.40 591 25.00 --------------------------------------------------------------------- Solar illumination 103 1.70 356 .60 --------------------------------------------------------------------- Electrolysis-_hydrogenomonas_ 55 .25 129 2.60 ---------------------------------------------------------------------

4 From [ref.174].

5 From [ref.175].

6 From [ref.176].

7 Includes instrumentation and food storage.

The values given in table IX indicate relative weights and powers required by various systems to provide the gaseous environment for manned s.p.a.ce cabins. If one considers operating temperatures and hazards, other systems may offer advantages which offset the weight and power advantages of the hydrogen reduction of LiOH systems.

Research is being conducted by NASA on life-support-system technology applicable to missions planned for 20 years in the future. Life-support systems include the requirements for supplying breathing gases, control of contaminants in the cabin atmosphere, water reclamation, food supply, and personal hygiene. The disciplines involved in such systems include biology and microbiology, cryogenic fluid handling at zero g, heat transfer, and thermal integration with other systems, such as power. The physiological, psychological, and sociological problems of the crew are also being considered.

Photosynthetic System

Green plants contain chlorophyll which captures light energy thermodynamically required to convert carbon dioxide and water into carbohydrate which can subsequently be transformed into other foods such as protein and fat. During this process, carbon dioxide is consumed, and an approximately equal amount of oxygen gas is liberated. As a first approximation, photosynthesis is the reverse of the oxidative metabolism of animal life:

Oxidation C6H12O6 + 6O2 -------> 6CO2 + 6H2O + heat

Photosynthesis 6CO2 + 6H2O + light -------> C6H12O6 + 6O2

The photosynthetic process in plants and respiration during photosynthesis have been studied intensively, and several metabolic pathways have been elucidated. Mechanisms are being studied to explain the inhibitory effect of strong visible light on this process. This program may lead to the use of chloroplasts or chlorophyll without cells in future photosynthetic bioregenerative systems for long-term s.p.a.ce travel.

One of the prime considerations of a closed ecological system is that the environmental gases shall remain physiologically tolerable to all of the ecologic components. Ideally, a photosynthetic gas exchange organism should possess a high ratio of gas exchange to total ma.s.s (considering all equipment and material incidental to growth, harvesting, processing, and utilization); and a controllable a.s.similation rate to maintain steady-state gas composition. It should also be (1) amenable to confining quarters which may be imposed by inflexibility of rocket or s.p.a.ce station design; (2) genetically and physiologically stable and highly resistant to antic.i.p.ated stresses; (3) edible and capable of supplying most or all human nutritional requirements; (4) capable of utilizing raw or appropriately treated organic wastes; and (5) amenable to water recycling as demanded by other components of the ecosystem.