Recent experiments on rodents confirmed that the action of cosmic rays in the planned flights to Mars threatens astronauts with memory, intellect and behavior disorders, characteristic of dementia. And this is just one of many factors that threaten the health of interplanetary travelers.
Following the science fiction writers
Scientists are seriously talking about sending a man to Mars for more than half a century – as early as 1952 the notorious Wernher von Braun published the book Das Marsprojekt , in which he outlined his thoughts on the technological aspects of such a mission. For the past since then, dozens of projects were offered by different organizations and researchers and more than a thousand technological experiments were carried out, but none of the projects reached practical implementation.
However, at the present time, the development of projects to send cosmonauts to Mars is being done by state space administrations, such as NASA, ESA and others, and private companies, primarily SpaceX and Boeing. All of them plan to achieve full readiness for flight in the 2030s.
In addition to the huge number of technological tasks related to the delivery, return and life support of the crew, the organizers of the flight will have to deal with the various negative consequences of long-distance space flight for the health of future colonists. Perhaps, it is in this direction that the least done so far.
Look around and forget yourself
The primary threat to the health of astronauts in distant missions is cosmic radiation, which is a stream of high-energy particles (mostly protons, as well as completely ionized nuclei of other elements) emitted by the Sun and galactic sources. People on the surface of the Earth and astronauts in low Earth orbit are protected from them by the magnetic field of our planet. Outside of its action, cosmic radiation exceeds safe limits for health, as confirmed by direct measurements, in particular during the flights of Mars Odyssey in 2001 and the Mars Science Laboratory in 2011-2012.
According to estimates made with the help of these devices, astronauts in the interplanetary space will receive approximately 400 to 900 millisieverts of radiation per year, which is close to the maximum permissible radiation dose for the whole career of an astronaut in low earth orbit. On Earth, this figure is an average of 2.4 millisievert per year.
According to statistics, the members of the lunar mission “Apollo” (only 24 people who have visited outside the Earth’s magnetosphere, eight of them by now dead) sharply increased predisposition to death from cardiovascular disease. Simulation in animals has shown that the most probable cause of this is the effect of cosmic radiation on the walls of arteries.
Other pilot studies in rodents indicate that radiation in space can cause degeneration of various tissues, including the nervous one, and contribute to the early development of Alzheimer’s disease.
To clarify the effect of cosmic rays on the organism of living beings, the staff of the University of California at Irvine irradiated the mice with high-energy charged particles (fully ionized oxygen and titanium nuclei) at doses comparable to those that cosmonauts can receive during long space flight.
As follows from a publication in the journal Scientific Reports , it was found that this effect causes a variety of long-term cognitive impairments associated with the work of the cerebral cortex and hippocampus. In particular, the executive functions decreased in animals, which underlie flexible, purposeful behavior, especially in unusual situations. As a result, they were not able to cope well with the formulation of tasks, their distribution over time and focusing on the main actions needed to achieve the goal.
At the same time, there was a deterioration in spatial, episodic and recognizing memory in the mice, as well as a decrease in the extinction of fear (the process of re-adaptation to something that caused a traumatic effect, for example, addiction to water after a drowning experience) and, consequently, increased anxiety. All these effects were observed for at least 24 weeks (for the mouse this is an important part of life).
At the cellular level, the effect of radiation caused inflammation of the nervous tissue, disruption of the integrity of the synapses, as well as the shape, density, and complexity of the dendrites of the nerve cells of the medial prefrontal cortex. This led to pronounced behavioral disorders.
The researchers note that such a cosmic radiation action not only threatens the astronauts with a disability, but also jeopardizes the fulfillment of the ultimate goals of the mission, since the revealed disorders directly concern decision making, the speed and adequacy of the reaction, the fulfillment of tasks and communication in the team.
In addition to violations of the central nervous system, do not forget about the more “usual” radiation effects associated with DNA damage and the development of active forms of oxygen that disrupt the structure of biological macromolecules. They include an increased risk of developing cancer, disrupting the internal organs, reducing immunity and a high incidence of radiation cataracts.
All these effects are associated with background cosmic radiation. If astronauts are on the way to relatively rare emissions of high-energy protons of the Sun, then they are likely to die from acute radiation sickness.
Not only radiation
Radiation is by no means the only factor that threatens the health of astronauts during the Martian (and any other interplanetary) mission. An extremely important role will also be played by prolonged exposure to zero-gravity. As evidenced by the experience of manned orbital flights, people living on the International Space Station (ISS) and various experiments, staying in weightlessness can have multiple effects on the body.
In the absence of gravity, there is no need for intensive work of systems, which on Earth it has to counteract. First of all, it is the musculoskeletal system and the cardiovascular system. In the conditions of weightlessness, muscle atrophy occurs with a decrease in strength, as well as a slowdown in cardiac activity, arrhythmia, redistribution of blood (it is manifested by facial swelling and sensory disorders due to increased intracranial pressure) and a decrease in oxygen consumption (which leads to a decrease in endurance) . Therefore, cosmonauts on the ISS have to regularly exercise on simulators, but even this does not save them from the need for a long adaptation after returning to Earth. The loss of liquid also contributes to its contribution – the volume of blood in astronauts can decrease by almost a quarter, which affects blood circulation and metabolism.
Bones in the absence of gravity begin to rapidly lose calcium and become more brittle. This process, called osteoporosis, leads to an increase in the level of calcium in the blood, which, in turn, promotes the formation of stones in the kidneys, constipation and (again) mental disorders.
Also, weightlessness disrupts the vestibular system, causing a condition similar to seasickness (although most cosmonauts adapt to it quickly). In addition, it can adversely affect the interaction of a person with his microbiome, although this issue requires additional radiation.
In addition to radiation and weightlessness, NASA in its 2015 report identifies three more groups of risk factors.
Connected with staying in the isolated space of the spacecraft:
- imperfection of control systems;
- various injuries;
- violation of the gas composition of air and possible penetration of cosmic dust;
- overwork and sleep disorders;
- possible action of toxic substances and pressure drops.
- cognitive and behavioral disorders (and here they are);
- difficulties with teamwork.
Connected with remoteness from civilization:
- lack of adequate medical care;
- unpredictable effect of treatment due to long-term storage of drugs under conditions of weightlessness and radiation, as well as possible changes in their distribution and utilization in the body.
To the flight are not allowed
To date, several ways to protect cosmonauts from these threats have been proposed. For example, radiation can protect additional passive shielding or electromagnetic shielding, and from zero gravity – artificial gravity by spinning a spaceship. However, their use is hampered by tight restrictions on takeoff weight and technological difficulties. At the same time, for some risk factors, prevention methods do not exist even theoretically.
Despite considerable funding (in 2014 only NASA spent more than $ 150 million on research in this field), there is not even adequate information on many health issues of interplanetary travelers (this is mentioned in the report already mentioned). Of the 25 factors identified in the planned NASA schedule to reduce the risk to the health of astronauts, only one is fully recognized and 12 are partially controlled to date. According to the same schedule, by the time of the first (unmanned) phase of the Martian mission, the only factor that will not be subjected to even partial control will remain cosmic radiation. It is with her that the greatest fears are connected.
The Office recognizes that a coordinated approach to protecting the health of cosmonauts in deep space has not yet been worked out. Other space agencies, too, can not boast of its presence.
So, when the engineers report on the technical possibility to proceed to the Martian mission, physicians and physiologists may have well-founded objections.