BIOMEDICAL SUPPORT OF PILOTED SPACEFLIGHT

Recent progress in the conquest of space and in piloted cosmonautics is the result of developments in space technology and hardware and, to a significant extent, has also depended on the solution of complex biomedical problems and other achievements in space biology and space medicine. During the period under discussion, the duration of space flight has increased to 14.5 months for men and 6 months for women. The long period during which the Mir orbital station was used (15 years) has generated unique experience in solving biomedical problems to ensure the safety and efficiency of increasingly long spaceflights.
Space medicine is basically a type of prophylactic medicine. Its duties include predicting all of the physiological consequences of exposure to spaceflight factors and preventing or curtailing likely disruptions in the functioning of various systems.
Support of piloted spaceflights involves a complex set of biomedical, technical, and organizational measures directed at creating the conditions required if normal human vital processes are to occur in space and using special means and methods to maintain cosmonaut health and performance at the level needed to ensure completing the standard flight program and for high crew efficiency if contingency or emergency situations occur.
Many years of research conducted by the Institute of Biomedical Problems jointly with a number of other organizations (see section on Space Life Sciences) has resulted in creating an efficient biomedical piloted spaceflight support system. This system includes
* cosmonaut medical selection and training;
* medical monitoring of cosmonaut status during spaceflight;
* providing medical care on board orbital stations;
* post flight cosmonaut rehabilitation;
* preventing the adverse effects of weightlessness; developing ways to prevent cardiovascular and musculoskeletal de-conditioning, disruptions of fluid-electrolyte metabolism, and sensory disorders;
* providing cosmonauts with food and water during flight;
* life support for spacecraft;
* maintaining radiation safety;
* maintaining cosmonaut safety during EVAs;
* sanitary and hygienic support of cosmonauts;
* developing optimal work-rest schedules and systems for psychologically supporting crews.
The overall program of measures performed by personnel working in space medicine is very extensive and includes three phases: preflight, in-flight and postflight (see Table 1).
Table 1. Program of Work in Space Medicine

Major Components of the Biomedical Support of Piloted Spaceflight

Medical Selection and Cosmonaut Training. Clinical physiological examinations of cosmonauts are undertaken to enable expert evaluation of their health in various phases of flight preparation and during the post flight period. The number of examinations and the intervals between them are specified by a special program (1). Before being accepted in the training group, candidates for crew membership undergo an inpatient examination, whose results are used to determine whether or not their health allows accepting them for the crew-flight-training program.
During the training phase, cosmonauts undergo dynamic monitoring, allowing specialists to
• detect latent incipient stages of disease;
• study personality characteristics and assess an individual’s functional and potential physiological capacities;
• develop recommendations determining the sequence and time line for various types of training and also measures for increasing physiological tolerance to exposure to spaceflight factors (2).
During the training period, crews periodically undergo detailed clinical physiological examinations to
• identify the characteristics of each cosmonaut’s physiological and psychological reactions to specific types of training;
• on the basis of health status and psychological traits, determine cosmonauts’ fitness for spaceflights of varying duration.
The medical commission uses the results of this comprehensive examination to decide whether to qualify crews for spaceflight.
Medical Monitoring of Cosmonaut Status During Spaceflight. Medical monitoring is an important component of the set of measures used to ensure crew safety during spaceflight. Such monitoring makes it possible to identify, analyze, and evaluate functional physiological changes exhibited by a cosmonaut, to assess whether use of prophylactic measures is indicated, and to select the optimum schedules for using them. An unusual feature of in-flight medical monitoring is that the patients are healthy, physically fit individuals. In addition, unlike medical monitoring on the ground, in-flight monitoring is remote—be-cause the subject and the medical personnel are separated by vast distances. Under these conditions, sources of information consist of data on the status of a cosmonaut’s physiological systems, the microclimatic parameters in the spacecraft or suit, the contents of radio communications between the crew and the Flight Control Center, and also special radio communication by the cosmonauts concerning how they feel during the flight. Telemedicine sessions, observations of crew actions, and monitoring how well they are performing their programmatic tasks serve as additional sources of valuable information (3).
The goals of in-flight medical monitoring include ongoing real-time monitoring of cosmonaut health status; identifying functional changes in physiological systems, and also of pathologies arising in flight; predicting potential for further continuance of the flight; planning and managing medical tests and prophylactic measures that facilitate retention of performance capacity in-flight and post flight; as well as monitoring the cabin environment, radiation conditions on the flight path, and adherence to the work-rest schedule, all of which are described in the respective portions of this article (4). In addition to this operational monitoring, periodically, crew members are subjected to more in-depth medical examinations, including administration of provocative (loading) tests to assess levels offunctional physiological reserve capacity. Furthermore, the medical monitoring system, if necessary, can be used to perform an immediate emergency medical examination and can be shifted to a mode of continuous recording of physiological parameters.
Means and Methods of Medical Care in Flight. The means and methods for providing medical care if cosmonauts develop illnesses or health disorders are considered of prime importance within the system for operational medical support of piloted flights.
The spaceflight medical support system is tasked with preventing disease, injury, and exposure to toxic substances and penetrating radiation, and also various different functional disorders evoked by exposure to spaceflight factors. The medical care system has the goal of providing timely diagnosis of health disorders and effective aid to any crew member who requires treatment during preflight training, in flight, or after return to Earth (5).
Although only healthy individuals are permitted to fly and all sorts of prophylactic measures are employed in flight to minimize the negative physiological effects of spaceflight factors, it is still not possible to preclude completely the occurrence of disease or other conditions that require medical treatment. Any such case is analyzed to identify possible shortcomings in the measures prescribed by the medical flight support system, and then the appropriate recommendations are derived.
The stressful operator activity, the metabolic shifts that occur in weightlessness and the changes in the reactivity of physiological systems may decrease resistance to adverse factors and damaging effects. This may lead to the development of neurasthenic symptoms (decrease in work capacity, susceptibility to fatigue, irritability, sleep disturbances), various inflammatory diseases and allergic states, and metabolic disorders of organs and tissues. Nor are such diseases as acute appendicitis or inflammation of the gall bladder or pancreas precluded during space flight because their occurrence is extremely difficult to predict even under normal conditions on Earth. Finally, emergency situations on board a spacecraft may lead to injuries, barotrauma, or poisoning.
The list of states that requires using prophylactic and/or therapeutic measures during spaceflight must include ”motion sickness,” the neurasthenic syndrome, local inflammatory diseases, and minor traumas.
The isolated nature of their living conditions, the unique conditions of their environment, and the limited number of crew members compel the cosmonauts themselves to bear responsibility for diagnosing illness and providing medical care.
All cosmonauts are adequately trained to provide medical care. If necessary, crew members, using onboard documentation, the computer database, and the capabilities of the telemedicine system can employ the appropriate onboard medical kit or medical procedures. Of course, the presence of a physician in the crew significantly facilitates medical monitoring and medical care and enhances their efficacy.
A special mobile unit equipped with all of the necessary medical instruments, which can be deployed at the reentry vehicle landing site, has been developed for use if it is necessary to give cosmonauts medical care immediately after landing.
System to Prevent Adverse Effects of Weightlessness. The system for preventing the adverse physiological effects of weightlessness includes a set of medical and technical measures that supports long-term human residence and work in space, including fostering appropriate adaptation to flight conditions and readaptation after return to Earth while fully maintaining health and performance capacity.
Weightlessness, which induces a number of specific adaptive changes in various physiological systems, may lead to the development of functional changes and to some structural changes as well.
In essence, the prophylactic countermeasures used today (see Table 2) are directed at preventing or substantially attenuating these adaptive processes, primarily to safeguard and facilitate the process of readaptation upon return to normal gravity. The two main goals of the system of prophylactic measures are to make up for the deficit in motor activity and to compensate for the effects of fluid (blood and interstitial fluid) redistribution typical of weightlessness (6).
On long-term flights, cosmonauts follow a schedule of prophylactic measures that has been specially developed for that flight on the basis of duration,flight phases, and the functional status of physiological systems. The following measures are included:
Table 2. Counter Measures in Space Medicine

1. Constant wearing of the “penguin” constant loading suit during all waking hours in the intervals between physical exercise sessions, including during the performance of professional duties. This suit applies lengthwise axial loading to the musculoskeletal system (from the shoulder girdle to the foot) to simulate weight loading and reproduces some degree of deformation and stimulation of the resistance and muscle receptors.
2. Two hours daily of physical exercise on the inboard exercise machines (VB-3 bicycle ergometer and UKTF treadmill) to maintain conditioning in the most important systems and retain overall physiological work capacity, activate venous pulsation and the circulation facilitating effects of muscle contractions, stimulate mechanoreceptors, and also foster retention of skills needed for maintaining a vertical posture and for locomotion. Physical exercise generally involves the UKTF apparatus, which consists of a treadmill equipped with a system of straps, individually fitted loading suits, special shoes, and an elastic harness. The treadmill permits cosmonauts to walk, run, jump, do knee bends, and lift “weights,” thus reproducing constant static loading along the vertical axis of the body and the effect of maintaining upright posture in gravity.
3. Electric stimulation of muscles—high frequency (using the Tonus-3 stimulator) and low-frequency (using the Myostim)—preferably after physical exercise, to maintain muscle strength, and static and dynamic endurance.
4. Use (in accordance with a specially developed schedule) of the “Chibis” suit, which creates lower body negative pressure and thus in weightlessness, reproduces the hydrostatic blood pressure pattern characteristic of Earth. During the early period of adaptation to weightlessness (week 1 of flight), if they so desire, cosmonauts use “Bracelet” occlusion cuffs and the “Karkas” and “Kentavr” devices to decrease the severity of blood redistribution effects.
5. During the flight, fluid and salt supplements are ingested to facilitate fluid retention and prevent symptoms of dehydration, and thus, help to increase endurance to acceleration and orthostatic tolerance. During descent, special couches and anti-g suits that increase orthostatic tolerance and endurance of gravitational loading are used.
6. A balanced diet (containing salts, amino acids, and vitamin additives) is provided to combat possible deficits in the food.
7. Use of drugs to affect certain physiological functions to eliminate adverse symptoms or exert a corrective effect (preventing and/or treating ”motion sickness,” maintaining of orthostatic tolerance, counteracting bone loss, and normalizing myocardial metabolism).
8. A set of psychological support measures to combat the adverse effects of spaceflight—isolation, a sealed, technogenic environment, excessive stress, and compulsory adherence to a nonoptimal work-rest schedule (7).
Preflight, to increase general physiological tolerance of adverse effects, nonspecific prophylactic measures are used, including endurance training, physical and special training, sleeping in head-down position, and breathing gas mixtures with diminished oxygen content.
Prophylactic measures directed at preventing or partially compensating for undesirable changes caused by weightlessness play an important role in maintaining cosmonaut performance level in flight and in ensuring their safe return to Earth.
Life Support on Board Spacecraft. A life support system (LSS) is a set of devices and systems, as well as supplies of food and other substances, required to maintain vital processes (metabolism) and human performance in pressurized spacecraft cabins. The LSS maintains the atmosphere in the closed cabin at a preset chemical composition and physical parameters (pressure, temperature, humidity, rate of movement), satisfies the crew’s need for food and water, and disposes of the wastes of the crew and other biological subjects. In accordance with these functions, the LSS is divided into a number of subsystems (components): air regeneration, water supply, food supply, thermal regulation, and sanitary and hygienic support. This is the structure of the typical LSS in the narrow meaning of the term. On long-term spaceflights, measures to maintain crew health and performance capacity are significantly enhanced. For this reason, the LSS also encompasses all devices and objects that satisfy the day-to-day cultural and aesthetic needs of the crew, provide physical exercise (weightlessness and the limited size of the inhabited portions of the spacecraft lead to a deficit in physical activity), and also provide radiation shielding.
LSS parameters are determined by the need to satisfy human requirements for food, water, oxygen, and for waste disposal. When LSSs are designed, all relevant factors are considered (purpose, type of spacecraft, duration of functioning, size of crew, characteristics of flight path, mass-energy constraints, safety, reliability, cost, and performance characteristics). The LSSs developed for Russian spacecraft are highly reliable, display stable performance under the influence of spaceflight factors, even in emergency situations, and are distinguished by their minimal power use, mass and size, and good maintainability.
As a function of the way they replace consumables, LSS subsystems are classified as either nonregenerative (based on stored supplies of the needed substances or supplies brought by transport spacecraft) or regenerative (the substances needed to support human life are recovered from biological wastes of humans and other spacecraft inhabitants) or mixed.
The LSS for the first spaceflight was designed on the ”nonregenerative” principle and provided the cosmonauts with a store of equipment and onboard supplies whose nature and amount was based on the caloric needs and the nutritive balance required by a healthy human on Earth. But, as flight duration increased and information accumulated on the dynamics of human metabolism under spaceflight conditions, there was a growing tendency to design and implement integrated regenerative systems, which utilized wastes and by-products of the functioning of various LSS components. Creating a completely closed LSS, simulating the processes of Earth’s biosphere, based on methods of abiogenic synthesis, remains a difficult challenge to this day. Partially closed LSSs, which regenerated water and the most important components of the atmosphere and also disposed of solid wastes, were developed for the flights of Salyut and Mir.
The formation of the spacecraft cabin atmosphere during flight is directly associated with the problem of atmospheric pollution. Sources of pollution may include construction materials and technological processes, as well as human waste products. The study of the biological effect of spacecraft atmospheric pollution is one of the more important problems that requires physiological and hygienic research. The practical result of such research is establishing of threshold limit values (maximal permissible concentrations) for a wide range of polluting (toxic) substances and developing of techniques for removing them from the spacecraft’s atmosphere (8).
So-called biological life support systems (BLSS) are based on a qualitatively new principle of environmental formation. The functioning of a closed biological system is based on the principle of repeated use of a relatively small initial quantity of chemical elements as the closed cycle transforms the substances of the system itself. To support human life, a BLSS must transform human waste products into food, oxygen, and water, that is, regenerate them. That such a system can exist in principle is obvious because the elements used by an adult organism are eventually emitted into the environment in the same quantities. Thus, for example, oxygen that is consumed oxidizing organic substances in food is emitted as a component of water and carbon dioxide, along with the hydrogen and carbon of the oxidized nutrients (9).
Systems based on biogenic synthesis are closest to conditions on Earth and thus to the biological needs of human beings, and are capable of self-regulation at all levels of the system by mutual correction of processes.
The first practical results in this direction were obtained in experiments on board Space Station Mir, when three complete developmental cycles of wheat ”from seed to seed” were completed in the station’s Svet greenhouse. Cosmonaut Nutrition and Water Supply In-flight. Sufficient and well-balanced nutrition of crews is one of the most important ways to maintain health and high psychophysiological energy and is the source of positive emotions in spaceflight. As flight duration and the degree of crew isolation increase, job pressure and responsibility are enhanced, and stress situations become more frequent, the importance of a diet adequate for cosmonauts’ physiological needs increases as well.
Onboard cosmonaut nutrition systems on Salyut and Mir were highly developed technological systems, including, aside from the food itself, the appropriate ”infrastructure” to ensure reliable storage and enable the crew members to prepare and eat their meals under spaceflight conditions. The nutritional systems components were functionally linked to the other life support subsystems, especially the water supply system, waste collection and disposal system, the power supply system, and the system maintaining microclimatic parameters (10).
Food rations (daily or for the whole flight) were appropriate to the cosmonauts’ caloric needs and contained the optimal amounts of nutrients (proteins, fats, carbohydrates, vitamins, and minerals). This was particularly true of the essential nutrients (certain amino acids, unsaturated fatty acids, and vitamins), which are insufficiently synthesized by the human body or not synthesized at all.
The major task of the water supply system was to ensure that the cosmonauts received a regular supply of water in quantities appropriate to their physiological needs to prevent the development of a fluid deficit in flight. Water is the largest component of the human body by weight, and its daily consumption exceeds the total consumption of oxygen and nutrients. This means that every day the cosmonauts were given ad lib access to a significant quantity of water of acceptable taste and odor, free from toxic contaminants and, if necessary, enriched with minerals.
On relatively short flights (up to 30 days), water supply systems based on supplies of potable water brought from Earth were preferred. As flight duration increased, it became necessary to have an entire water generation cycle take place on board the spacecraft. For this purpose, the space stations were provided with systems for regenerating water from low concentrated (concentrates of atmospheric moisture and process water) and highly concentrated (human urine and wash water) solutions for repeated use. The problem of in-flight water regeneration also encompasses problems of conditioning the taste and the chemical, as well as the bacteriological, properties of the regenerated water before it is used for drinking or reconstituting dehydrated food (11). Sanitary and Hygienic Support of Cosmonauts. Sanitary and hygienic support of cosmonauts includes a wide range of problems relating to maintaining conditions in the spacecraft cabin where they live and work that are conducive to crew comfort and well-being. This includes developing hygienic standards and prophylactic measures for maintaining the spacecraft crew’s health and performance capacity, providing cosmonauts with clothing and means of personal hygiene, waste disposal, maintaining cosmonaut microflora in an optimal state, and maintaining the spacecraft atmosphere and surfaces (12).
The significance of the personal hygiene component of the biomedical flight support system has grown as flight duration has increased. Various technological processes and measures were used to satisfy crew-members’ sanitary and hygienic needs. Here, the significance of hygienic procedures was dictated by hygienic and physiological considerations and also mainly by psychological/aesthetic, epidemiological, and possibly toxicological concerns.
The criteria for selecting personal hygiene devices and techniques included inducing a sensation of bodily cleanliness after the procedure had been completed and also the feeling of ”refreshment” and psychological comfort.

Personal hygiene measures included four basic types of procedures:

• complete cleansing of the body;
• washing of certain portions of the skin;
• oral hygiene;
• haircuts, shaving, and nail care.
Dry and wet (moistened with special washing and cleaning solutions) wipes and towels were used to cleanse the body. The wipes provided adequate skin cleaning and refreshment. In addition, they could be used to wipe down the surface of the spacecraft cabin.
Oral hygiene was considered an important personal hygienic measure. It involved regular cleaning of the teeth and rinsing of the mouth. Various types of toothbrush, toothpaste and powder, toothpicks, mouthwash, and rinses were used for this purpose.
Hygienic treatment of the hair consisted of periodic haircuts and shaving of the beard and mustache. The main problem in hair care during space flight is preventing fragments of hair or beard from getting into the cabin atmosphere.
The saying that the best clothing is that whose presence cannot be felt is highly applicable to cosmonaut clothing, which must be comfortable for working and relaxation and should not impede or limit motion. The cosmonaut wardrobe consists of underwear, a flight suit, which the cosmonaut wears inside the spacecraft, and a thermal suit. The fabrics specially selected for cosmonaut underwear were light and elastic, did not impede heat convection and radiation or evaporation of moisture from the body surface, and at the same time were strong enough to be worn for long periods of time and to allow attaching sensors for recording biotelemetric information.
The flight suit was fully compatible with the underwear and thermal suit. Its design allowed freedom of motion and made using sanitary facilities convenient. It was easy to put on and take off. One of the main functions of the flight suit was to maintain the cosmonaut’s thermal balance by preventing both excess heat loss and accumulation of excess heat. The thermal suit is designed to be used on landing in a deserted spot under adverse climatic conditions. In addition, it may be used if the spacecraft air conditioning system does not function properly. The thermal suit set included shoes, which had to be light, strong, and to have good thermal insulation properties. This was achieved by selecting the appropriate materials and design, which also account for the fact that the cosmonaut would have been adapted to weightlessness (13).
In closed pressurized cabins of limited size, the presence of even small concentrations of harmful substances in the atmosphere may have a serious effect on human health and performance capacity. The sanitary hygienic subsystem included studies of sensory parameters and chemical analytic tests of the air, which made it possible to identify the nature and rate of the off gassing of harmful substances from polymers and wastes. One of the main sources of atmospheric pollution in a pressurized environment is the human body, which releases a large quantity of metabolic products through the lungs, skin, kidneys, and intestinal tract. The amount of volatile chemicals emitted by a person varies within broad limits and depends on a number of factors: the nature and quality of the diet, metabolic status, and the nature and intensity of work performed.
Polymer materials are a second, no less important, source of atmospheric pollution in a pressurized cabin. Polymer synthesis involves using a number of auxiliary compounds that belong to a number of different classes and have an extremely broad spectrum of toxic effects.
The concept of ”wastes” encompasses the set of products that form as a result of human vital activity and the operation of the equipment installed in the spacecraft cabin and not subsequently used. Regardless of chemical and bacterial composition or physical and other properties, wastes have one basic property in common. They are one of the sources that pollute living and working areas with undesirable or harmful substances and foster the development of microflora, some of whose species can cause illness in crew members or damage equipment (14). Correct structuring of waste containment and disposal is one of the major requisite conditions for maintaining normal vital processes and high performance capacity in spacecraft crew members.
However, the technical implementation of these operations under the unique conditions of spaceflight encounters a number of difficulties. The great majority of wastes are gaseous or liquid. Experience with space stations Salyut and Mir has shown that collection and transport of substances in this state present great technical difficulties in weightlessness.
Research on the problem of microbiological damage (biodegradation) to structural materials was initiated when Salyut-6 was in use and continued on all subsequent Soviet and Russian orbital stations. It was established that spacecraft microclimatic parameters, i.e. the presence of specific chemical contaminants in humidity condensate and anthropogenic pollution (with human metabolic products) are the stimulating factors for growth of bacteria and mold on the materials of the cabin interior and equipment. More than a 100 species of microbes—bacteria and fungi—have been isolated from the surfaces of these materials during long-term spaceflights. Among these were species that present potential danger to human health, the so called pathogenic saprophytes, which can grow actively on artificial substrates, and also nonpathogenic bacteria and fungi that damage (destroy and degrade) various materials (metals and polymers) and thus cause failures and disrupt instrument and equipment operation.
Because, cosmonauts may show symptoms of dysbacteriosis or develop states of immunodeficiency from the effects of spaceflight factors and the processes of pathogen recirculation are intensified in a small pressurized cabin, the risk of spread of infection among crew members increases. All of this motivated the development of a microbial spacecraft safety system, which stipulated, in particular, that during preparations for flight, only structural materials that had been, in ground-based simulations, most resistant to microbial action were to be selected and that special disinfecting measures be undertaken. During spaceflight, the system called for treating spacecraft cabin surfaces, including the spaces behind instrument panels, with wipes moistened with special antibacterial and antifungal agents (fungistats). Experience with long-term flights on Salyut and Mir demonstrated that this system is highly effective. Maintenance of Radiation Safety in Spaceflight. The radiation safety system is a set of means and measures directed at preventing and precluding the adverse effects of ionizing radiation (for example, during powerful solar flares or flights in Earth’s radiation belt) on cosmonauts. These means and measures include physical screening of inhabited spacecraft modules, additional local screening of cosmonauts (radiation shelters), pharmacological and chemical protection of cosmonauts, inboard radiation monitoring devices, and the results of monitoring the radiation situation by the Solar Service (15).
Measures directed at ensuring crew safety include predicting the level of cosmonaut radiation exposure during the planned flight, developing initial recommendations for constructing piloted spacecraft, analyzing the radiation conditions in the flight path, radiation monitoring in the spacecraft cabin and station orbits, evaluating of levels of radiation exposure; developing recommendations to keep irradiation from exceeding the threshold limit dose, and providing cosmonauts with complete and current information.
The high biological interaction of various types of cosmic radiation makes them dangerous. For this reason, a research study was undertaken to determine acceptable levels of radiation exposure and to develop means and methods for prevention and for shielding cosmonauts from cosmic radiation.
By now, many techniques and devices have been developed to measure absorbed dose, dose equivalent, particle flow, linear energy transfer spectra, charge and energetic spectra and spectra of particle mass; each serves a strictly defined measurement function.
Radiation monitoring systems may be classified as active or passive. In active systems (including tissue equivalent ionization chambers, microdosimeters,and particle spectrometers), instrument readings are recorded by crew members in orbit or are telemetered to Earth in realtime. In passive systems (including thermoluminescent dosimeters and dielectric track detectors), the readings are recorded and analyzed after the spaceflight has been completed.
Evaluation of radiation risk involves assessing the likelihood of specific adverse somatic effects (ASE) on human health as a result of exposure to ionizing radiation. The conception of risk from the effects of ionizing radiation assumes that the likelihood of developing ASE is directly proportionate to dose equivalent. In this case, the likelihood of ASE is the product of two contingent probabilities: the likelihood that a person will be exposed to a given dose equivalent and the likelihood that the dose equivalent will provoke ASE.
The risk to humans of cosmic radiation in flight may be minimized by a number of measures to decrease the likelihood of ASE to a justified (minimal reasonably acceptable) level, that is, according to the “ALARA” (as low as reasonably achievable) principle. The concept of a reasonably acceptable risk makes it possible to decrease it, comparing advantages and disadvantages, under the assumption that certain threshold limits on a momentary dose of irradiation are the upper limits of the safe level of exposure. It follows from this that a dose limit exists (the lowest level) that is absolutely unacceptable to exceed if there is to be any further exposure. Thus, it is not sufficient to decrease radiation exposure to a level below the dose limit; rather risk must be limited by reducing all radiation exposures to the minimally reasonably acceptable level.
In accordance with the standard dose limits adopted in Russia, the amount of irradiation to which a cosmonaut’s hemopoietic organs have been exposed throughout the entire period of his career must not exceed 1 Sv (16). This dose limit has been established to limit the adverse remote effects of cosmic radiation. To avoid immediate radiation effects during flight, which may decrease in-flight performance capacity, dose standards for shorter periods have also been adopted. For example, the annual dose limit is 0.5 Sv, and the monthly dose limit is 0.25 Sv. On 1-year orbital flights, the total dose did not exceed 0.2-0.25 Sv, although there is some small probability that this value should be increased significantly to account for powerful solar proton events. Thus, the adopted dose limits and the radiation conditions characteristic of near-Earth orbit permit increasing space flight durations on these paths to up to 4-5 years.
In practice, radiation risk may be decreased by regulating the amount of time an individual spends in the cosmic radiation field and also by designating an area within the spacecraft that has a low radiation dose rate where the cosmonauts spend the majority of their time. Radiation risk may be decreased during the spacecraft design phase by selecting the best materials for radiation screening to prevent particles from penetrating the interior of the spacecraft cabin and also by minimizing induced radioactivity. The total whole body radiation dose as well as the dose to certain organs can be significantly decreased by local screening of these organs and areas of the body. Moreover, medical prevention and treatment methods are being developed (use of radioprotectors, prophylactic biomedical drugs, and postradiation therapy) that may enhance reparative processes in affected tissues. There is also a possibility that proactive genetic selection of cosmonauts could be used (selection of individuals who are highly resistant to the effects of radiation or whose tissues can rapidly recover from radiation damage).
Psychological Support of Long-Term Flights. The increase in spaceflight duration and the complexity of flight missions have substantially increased the priority of the human factor in the “cosmonaut-spacecraft” system. Solution of problems relating to human psychological stability on long flights involves considering a large number of behavioral factors: psychological needs; subjective states; anxieties; interactions with colleagues on the crew and on the ground, for example, at the Flight Control Center; role-based relationships; work planning; criteria for success; and an external motivation system. The difficulty of maintaining psychological stability in a crew increases as flight duration begins to be measured in years.
One of the problems of space psychology is how to increase the psychological and professional reliability of cosmonauts. The solution of this problem will require improving the means and methods of selection, training and crew formation, and of evaluating cosmonauts’ psychological status. Prevention and correction of psychological disadaptation is extremely important here and must entail investigating the characteristics of group dynamics and the chronobiolog-ical aspects of adaptation, as well as optimizing cosmonaut professional performance (17).
Improvement of crew living and working conditions on board the spacecraft attenuates the psychogenic consequences of living in an artificial environment. During preflight training, a cosmonaut masters the necessary professional skills and knowledge and the skills involved in group dynamics. On this basis and also based on their own beliefs and expectations, cosmonauts construct their own individual representation of the upcoming spaceflight.
One particularly significant psychological problem that arises in connection with the increased heterogeneity of space crews in nationality, gender, profession, and other characteristics is the problem of optimizing the psychological climate in a heterogeneous crew, ensuring that effective independent group decisions are made, and that international space crews interact successfully with national flight control centers. In this context, the crew training phase, during which cosmonauts must develop mutual trust, a common system of values, and a strategy for managing and resolving problems as a team, takes on additional significance (18).
During the first 4-6 weeks of flight, cosmonauts come to terms with the living environment in the spacecraft. During this period, they must cope with new sensations, impressions, and characteristics of movement. In this situation, cosmonauts require additional time to prepare for and implement their professional tasks and to set up interactions with specialists in ground services. This may lead to time pressure and fear of not completing tasks on schedule, which creates conditions conducive to emotional stress and fatigue.
Next comes a phase of physiological and psychological stabilization; however, the crew members begin to feel an intense desire for new information as a result of the ”sensory deprivation” they are experiencing. The novelty of spaceflight begins to lose its significance for them, as they get used to the unfamiliar living and working schedule and conditions. The effect of these factors can lead to diminished psychological tonus, development of symptoms of debilitation, and disruption of the “sleep-waking” cycle.
In the period 15-30 days before landing, crew members enter another phase of psychological adaptation—emotional reorientation—as they begin to focus on imminent return to Earth.
The shift to long-term space flights, the way to which was paved by technological progress and the new capacities of space technology in the 1970s, required well-grounded safeguards that crew members would retain their health, high performance capacity, and the ability to work without “breakdown.”
As part of medical flight support, a great deal of attention is paid to monitoring the crews’ work-rest schedules. Information is collected about planned and actual cosmonaut schedules, these data are analyzed immediately, and scientifically justified suggestions and recommendations are generated for immediate adjustment of the schedule on one- and multiday time scales. The work-rest schedule is then revised, taking into account the crew’s status and progress in flight program implementation.
Maintenance of normal rhythms in physiological functions takes on critical significance on long-term flights. The planned work-rest schedules of Salyut and Mir cosmonauts were based on the familiar 24-hour schedule without displacing the “sleep-waking” cycle. However, in a number of instances, the need to perform such critical tasks as launch, docking, EVAs, and others compelled occasional shifts in the phases of the cycle.
Each shift of this kind represented stress and led to additional pressure on regulatory systems. In cases like this, special measures were taken to minimize the adverse consequences of these shifts and prevent desynchronosis.
In addition to the duration of crew work shifts, each member’s interest in various types of task was studied, as was the relationship between their level of motivation and the quality of their work.
A number of effective quantitative methods were developed to aid in objective assessment of cosmonauts’ psychological status on long-term flight, and these have been used successfully in medical support of piloted flights, including flights of international crews.
Although the structuring of the crew’s lives on long-term space flights is limited by technical capacities, medical personnel and psychologists have labored intensively to improve conditions for living and working in space and to attenuate the psychogenic consequences experienced by crew members because of shortcomings in the artificial living environment.
The concept of ”psychological support” was introduced to space medicine in connection with the support of space-station flights of increasing duration. Cosmonauts who have made long-term flights unanimously acknowledge that the standard system of psychological support is an important factor in maintaining a normal sense of well-being and performance capacity under such conditions. Generally, the aspect that has the most important role is the opportunity to have private conversations with their families and unstructured communications sessions with their relatives, friends, and various public figures.
The system of psychological flight support for cosmonauts is directed at optimizing the psychological status and performance capacity of healthy individuals, prevention of psychological and psychophysiological impairments, and support of harmonious psychological interactions within the crew. Only through effective use of psychological and personal reserves of strength during a flight is it possible to avoid developing undesirable neurophysiological changes (diminished performance capacity, disruptions of sleep, debility, and conflict stress) that occur as a result of adverse psychological spaceflight factors: heightened risk, sensory deprivation, monotony, heightened responsibility for performance of flight operations, and the limited and imposed nature of social contacts.
Psychological support, which is generally not based on the use of drugs, makes it possible to compensate effectively for the deficit in social contacts (teleconferences with relatives and friends), the information deficit (news broadcasts and Internet access), and gives the cosmonauts the opportunity to feel the importance and interest those on the ground attach to the results of their work and their constant concern and attention to them as individuals (through packages containing their favorite topics, films and music, and congratulations on dates of personal importance). Particular significance is attached to compensating for the loss of accustomed terrestrial stimulation—landscapes and sounds of nature— which are reproduced on special video and audio programs, produced with help from cosmonaut friends and family members. If necessary, cosmonauts can talk to psychologists on a confidential channel. Constant work with the families of crew members makes it possible to optimize the psychological climate surrounding each cosmonaut, to prepare family members for communicating with the space station, and to facilitate subsequent post flight psychological rehabilitation.
Space medicine and space psychology have developed objective methods for daily psychological monitoring of cosmonaut psychophysiological status and performance capacity, as well as of the psychological climate of the crew as a whole. Diagnoses are made by analyzing radio conversations with the crew as experts make ratings on specially developed scales. Significant diagnostic information regarding performance capacity is provided by the onboard psychodiagnostic system. In addition, each cosmonaut’s pattern of psychological and emotional reactions to various situations, including extreme ones, has been charted preflight. The diagnostic information obtained is used to plan problem-oriented psychological support measures; predict changes in psychological status and work capacity in subsequent phases of the flight; and provide recommendations to flight directors on the advisability of a cosmonaut performing key operations — night work, docking, and EVA.

Methods of prevention and correction include the following:

• special preflight training;
• measures to optimize professional performance;
• formulation of positive feedback that acknowledges the success of tasks performed;
• measures to counteract the ”asthenic syndrome” (dysthymia) and eliminate nonspecific anxiety components, including the use of drugs.
Support of Cosmonaut Safety During EVAs. EVAs are an important and effective operation performed during space flight. During the period Soviet and Russian spacecraft were used between 1965 and 2000, a total of 96 EVAs were performed by 51 different cosmonauts (including one woman). Cosmonauts performed an enormous amount of work during these operations; they conducted unique scientific experiments, transported and mounted large structures on the space station exterior, performed various repair and debugging tasks, tested self-contained manned maneuvering units, and inspected depressurized modules. The maximum duration of an EVA from opening to closing of the access hatch was 7 hours 14 minutes by A. Solvyev and N. Balandin in 1990 (19).
The EVA medical support system includes monitoring during training, EVA implementation, and post-EVA. At present, there are no specific medical requirements for crew members who conduct EVAs. They undergo obligatory training on a technical trainer, learn about the EVA suit and study a number of operations that crew members will have to perform.
Four basic technical trainers are used: a setup enabling training in the absence of weight loading (hydrolaboratory), a full mock-up of the spacecraft, high-altitude barochambers, and a simulator of space suit system failure modes. The hyrdolaboratory is typically used in constructing and testing various spacecraft components, apparatus, and crew equipment, and also for developing work techniques for the crew and determining what work operations can be performed during EVA within the limit loading values. Moreover, it provides wonderful opportunities for conducting preflight cosmonaut training. Here, cosmonauts become familiar with the schedule of planned operations and master skills of locomotion under conditions maximally simulating those of weightlessness. Before each submersion in the water, crew members undergo a brief medical examination and while they are submerged, they are subject to constant physiological monitoring.
Physiological criteria for EVA on long-term spaceflights include evaluating the possible effects of microgravity on crew performance efficacy. This means that every change in a physiological system, including changes in proprioception, strength and muscle mass, cardiopulmonary deconditioning, bone demineralization, and effects on vestibular functioning and gas exchange, may have some relation to the crew’s readiness to perform an EVA effectively. For this reason, as part of EVA preparation, 2 weeks before the EVA, crew members undergo a comprehensive medical examination, including provocative tests on the bicycle ergometer.
During an EVA, the ground services, in addition to recording technical space suit parameters, monitor physiological parameters (EKG, pneumogram, body temperature, and caloric expenditure).
During and after an EVA, cosmonauts may develop various problems that require the attention of experts in space medicine. These may include
• general and local (midsized and small muscles of the arms) fatigue;
• pressure sores and blisters on the hands;
• emotional stress;
• shifts in thermal status (chilling, overheating);
• symptoms of high-altitude decompression sickness.
To prevent altitude decompression sickness brought on by the shift from the low working pressure inside the space suit (330mmHg) to the normal atmospheric pressure within the spacecraft, immediately before the start of the EVA, crew members prebreathe pure oxygen at a pressure within the space suit of 533 mmHg for denitrogenation (20).
Postflight Medical Rehabilitation. Despite cosmonauts’ use of measures provided by the prophylactic system, exposure to adverse spaceflight causes them to exhibit certain changes in the cardiovascular system’s tolerance of the orthostatic position and in the characteristics of bone and muscle tissue, metabolic shifts, and vestibular and sensory impairment (see Biological Responses and Adaptation to Spaceflight: Living in Space—An International Enterprise), which require them to undergo medical rehabilitation postflight.
A system of rehabilitative and therapeutic measures has been adopted using data generated by clinical medicine, previous orbital flights, and ground-based simulation studies to help cosmonauts adapt to conditions on Earth, effectively restore their altered physiological functions and performance capacity, and ensure their professional longevity.
The specific rehabilitation program is based on
• the flight program (its duration and crew workload);
• characteristics of the crew-members’ adaptation to spaceflight conditions;
• severity of fatigue (debilitation) during the flight;
• postflight changes in a cosmonaut’s feeling of well-being and health status;
• individual characteristics of crew members and their preferences.
Structurally, the rehabilitation period consists of the following phases:
* meeting the crew at the landing site and evacuating it to a specialized rehabilitative and therapeutic base;
* readaptation at the rehabilitative-therapeutic base;
* recovery at a sanatorium or health spa.
The goal of the first phase is to provide a safe, nonstressful transition to conditions of normal gravity. This is achieved by limiting orthostatic, physical, and vestibular stress and through use of postflight prophylactic suits.
The most critical stage of readaptation, which takes place at a specialized rehabilitation and therapeutic base, lasts an average of 2-3 weeks. The major goal of this period is restoration of previous functional physiological status. During this phase, motor activity is gradually increased, and different techniques of rehabilitation (calisthenics, massage, and workouts in the pool and on exercise machines) are sequentially introduced. Loading is increased by increasing the rates of walking, running, or swimming, decreasing the duration and number of rest periods, and increasing the number of exercises and their difficulty.
Creating a favorable psychological climate and positive emotional factors are considered highly important. In addition, selecting and sequencing rehabilitation methods are based on the results of comprehensive batteries of postflight clinical and physiological tests.
The sanatorium/health spa phase of rehabilitation lasts for the next 20-30 days. Factors considered in site selection include climatic conditions at the time of year, level of equipment at the sanatorium, and the preferences of the crew members. During this stage, extensive use is made of climatic factors, physical therapy, and mud baths, the methods of therapeutic exercise and physical training, and long-distance running along a natural course. The rehabilitation and therapeutic methods employed are directed at completely restoring health status and functional physiological reserves. An individualized approach is used for prescribing procedures, accounting for health status and the temporal course of recovery and also of the capacities and desires of the crew members. Postflight psychological rehabilitation (the final phase of psychological support) is considered a very important part of this process. Such rehabilitation is directed at restoring social contacts, which have been partially lost (including family ties), as well as psychophysiological reserves that have been depleted under the extreme conditions of spaceflight (21).

Future Prospects for Developing the Biomedical Flight Support System

From a medical point of view, the use of the International Space Station (ISS) will be characterized by
• an increase in crew size and in the heterogeneity (including nationality) of the payload specialists involved;
• heightened work intensity, use of multiple shifts, an increase in the number of EVAs, and increased complexity of the EVA programs;
• permanent capacity to evacuate sick and injured from the ISS using specialized rescue spacecraft.
These characteristics will determine the set of specific medical, engineering psychological, and ergonomic tasks that must be performed, including
* developing criteria for a differential approach to selection and flight qualification for individuals who vary in initial health status, age, and gender;
* establishing criteria for permissible and optimal duration, the number of repeated flights, and the interval between them for various groups of cosmonauts;
* developing a system for medical support of rescue work;
* developing a system of measures for medical support of space crews whose members do not fully meet standards (for example, space tourists); this requires an individualized approach to regulating schedules of work, rest, meals, physical training and to conducting medical monitoring and therapeutic and preventive treatments;
* developing measures to support the safety of group EVAs for conducting planned work and rescue operations;
• developing a scientific basis for specifications of the ergonomic characteristics of the ISS, the structure and particular methods of medical support, and the functions of the crew physician.
Current attainments in this area are a good foundation for further progress in solving biomedical problems presented by future piloted space projects, including the Mars mission.
The isolation of the crew on a flight to Mars will require significantly more reliable safeguards both for the spacecraft systems and for the medical flight support system. The impossibility of emergency return of the crew to Earth or replacement of a sick crew member make it absolutely essential that a highly qualified physician-cosmonaut take part in the mission. An automated system for collecting, transmitting, and analyzing biomedical information and data banks and databases is already being created for the medical support of such autonomous spaceflights.
Another of the most important conditions to support a Mars mission is successful solution of a set of psychological problems, including psychological readiness to accept risk and to perform tasks at the limit of psychological and physical capacities and to resolve nonstandard contingency situations while living in isolation from Earth. An obligatory condition for inclusion in the crew must be a candidate’s previous experience with long-term flights, because an interplanetary flight will mobilize all of the individual resources of the crew.
We will have to develop a more biologically complete and ecologically based artificial living environment fully appropriate to long-term human needs. We must create an analog of Earth’s biosphere on board the Mars spacecraft, whose active components will be human beings, animals, plants, and microbes. Once this is accomplished, existing LSSs will be replaced by a regenerative LSS with a high coefficient of cycle closure. Laboratories on Earth have already produced encouraging results.
Another important problem is protection from galactic and solar cosmic radiation, which increase significantly outside the bounds of the radiation belts. On long-term interplanetary voyages, we will have to contend with the risk of mutagenic processes and also with threats to the lives and health of our cosmonauts. Approaches to ensuring radiation safety under these conditions may include selecting certain periods of solar activity for flights, creating a radiation shelter on board the spacecraft, and possibly, using pharmacological protective agents.
The risk of a Mars expedition is significantly higher than that associated with human presence in near-Earth orbit and thus interplanetary missions must be preceded by intensive in-depth research in the area of space physiology, psychology, radiobiology, life support systems, and the development of reliable means for protecting and maintaining the health of cosmonauts. For this purpose, along with the obligatory use of existing ground-based experimental bases and devices, we will need to make maximally effective use of the potential of existing and planned space stations and unpiloted biosatellites, which will allow us to create a strong foundation of global cosmonautics to conquer the planets of the solar system (22).

Glossary

ASE. Adverse Somatic Effect
BLSS. Biological Life Support System
EKG. Electrocardiogram
EVA. Extravehicular Activity
ISS. International Space Station
LSS. Life Support System
OS. Orbital Station
Sv. Sievert