The main sources of radiation in space

An international group of scientists from 20 organizations from around the world with the participation of specialists from the Moscow Institute of Physics and Technology (MIPT) compiled a list of activities to improve the radioresistance of the human body . Resistance to ionizing radiation is a prerequisite for successful space colonization, scientists say.

Radiation resistance is the immunity of cells, tissues, organs or organisms to the effects of ionizing radiation. It is known that many living organisms on Earth have an amazing radioresistance. For example, the bacteria Deinococcus radiodurans and slow-movers are able to withstand the highest dose of ionizing radiation of about 5000 grays (5 million rad), that is, 5 kilojoules per kilogram of mass, while doses of more than 1000 grays make the slow-movers infertile. At the same time, for a person a lethal dose is considered only 4–10 gy . The record among living organisms belongs to the Archaea-extremophile Thermococcus gammatolerans , which is guaranteed to be killed only by radiation of more than 30,000 grays .

Cosmic radiation and microgravity are the two main factors affecting human health when in space outside the protective magnetic field of the Earth. These factors significantly limit the prospects for long-term space flights. It must be recognized that the need to protect the human body from the harmful effects of cosmic radiation is largely ignored. For example, Ilon Musk planned the beginning of the Martian colonization for 2024, but he never presented a comprehensive radiation protection scheme.
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But for flights to deep space, including a flight to Mars, radiation exposure is one of several categories of unacceptable risk , since the total doses received by astronauts will surely significantly exceed the dose limits established under the current NASA radiation protection system . In accordance with the NASA paradigm, the maximum limit on the risk of death due to radiation exposure is set at 3% for traveling to Mars. That is, out of six astronauts with a probability of 83% must survive five (0.97 ^ 6), and out of twelve with a probability of 69% eleven (0.97 ^ 12) will survive. This is an acceptable result. Among all the fatal cases, mostly death will come from malignant tumors (cancer), analysts say.

In order to achieve mortality within the normal range (3%) or lower, it is necessary to introduce additional protection systems, including new biotechnological concepts, which will solve this problem and give an opportunity to begin the era of manned flights into deep space.

The main components of cosmic radiation are solar proton events (SPS) and galactic cosmic radiation (GCI). Obviously, the contribution of ATP to the total radiation dose of astronauts will be insignificant during long missions far from the Earth and the Sun. Consequently, the main type of radiation in the effects on the body is a SCI, consisting mainly of high-energy particles.

In principle, ionizing radiation interacts along tracks of charged particles with biological molecules, such as DNA. The process is largely stochastic and can damage DNA through direct interactions (for example, ionization and excitation) or through indirect interactions, such as the production of reactive oxygen species as a result of the radiolysis of water molecules.

It is estimated that traveling to Mars and back will expose astronauts to radiation doses of 660 mSv. Although there are large uncertainties regarding the estimates of the risk to health (cancer) from exposure to cosmic radiation, this dose alone accounts for more than half of the total exposure limit for a NASA astronaut who is set at 800-1200 mSv . Obviously, in accordance with the principles of radioprotection currently in force, longer missions will become unacceptable to people in terms of the risk of cancer.

Currently, the European Space Agency (ESA) is conducting intensive research into the possibility of long-range space flight. Given that the flight will occur mainly under the control of automatic systems, where the participation of astronauts is practically not required, the space crew will be literally imprisoned for many months without any work. Such situations can be dangerous, especially for the astronauts themselves. Therefore, the ESA believes that it is wiser to immerse people in hibernation (hibernation, that is, hibernation). Currently, ESA has begun to implement the Aurora project, where it is considering the option of hibernation of the crew . Scientists intend to use biological mechanisms that will allow the crew to sleep and thus reduce the body's metabolism to an absolute minimum.

It is worth emphasizing that the idea of ​​possible hibernation during long space flights was also investigated in the USSR in 1969, but, unfortunately, after the death of the head of the Soviet space program Sergei Korolev, the project of the manned Soviet mission to Mars was closed, and all work related to it implementation, discontinued. The results of these studies included data on hyperresistance to various damaging factors, including lethal doses of ionizing radiation, long-term fatal overloads and hypobaric hypoxia in mice (see the book “Hypobiosis and Cryobiosis: Past, Present and Future” by Nikolai Nikolaevich Timofeev, MD, specialist in the field of aviation and space medicine, head of the laboratory of nanocytophysiology of the Institute of Nanotechnologies of the International Fund for Conversion).

There is a theory that radioresistance can be trained by pre-irradiating the body with small doses of ionizing radiation. It is well established that radioresistance can be genetically defined and inherited in at least some organisms. There are also drugs with radioprotective properties:

• the preparation en: Ex-Rad (ON 01210.Na), which is the sodium salt of 4-carboxystyryl-4-chlorobenzyl sulfone;
• en: CBLB502;
• amifostine (en: amifostine) 'WR2721';
• filgrastim ('Neupogen');
• pegfilgrastim (en: Pegfilgrastim) ('Neulasta');
• kojic acid

The published work lists possible ways to reduce the health risks of astronauts from ionizing radiation. Scientists propose several approaches: medical selection of radioresistant radiation-resistant candidates (and their descendants to which genes are transferred), tissue regeneration technologies and cell therapy, genetic engineering, gene therapy, experimental evolution, hibernation, biobanking, etc.


Ways to reduce the health risks from cosmic radiation during space travel

No screens yet

Due to the very high energies of the GKI charged particles, they easily penetrate into passive protective materials. Despite the fact that active screening technologies are also currently being studied, significant progress has not yet been achieved in significantly reducing the flow of GKIs to levels suitable for long-term human space flight (see the analysis of the effectiveness of all possible options for active protection ).

In this regard, it is important to explore the various prospects for improving human radioresistance using the latest advances in biotechnology. So, what are the ways to improve the radioresistance of scientists.

Ways to improve radioresistance in humans

1. Conducting genetic changes using breakthrough technologies in gene editing, combined with modern knowledge of molecular ways to counter radiation-induced DNA damage.
2. Regenerative medicine.
3. Low-dose radio adaptation.
4. Use of deuterated organic compounds.
5. Biostasis (a significant slowdown in all vital processes in the body).

Perhaps a combination of all these methods.

In addition, a lot of attention in this scientific work is paid to radio protection. Some of the ideas could potentially be used to alleviate other detrimental effects of long-term space travel, such as deterioration of muscles and bones, the authors say. The described biotechnologies such as genetic engineering, regenerative medicine, biostasis and cryogenic sleep in the future may find application not only in astronautics, but also in terrestrial medicine, including for the extension of human life.

“In this paper, we study the foreseeable options that can be used to increase human biomedical resistance for exploration and colonization of space. It also aims to identify the relationship between aging, longevity and radioresistance, and it also explores ways in which research on improving human radioresistance could synergistically improve people's health. Ultimately, we study how working in a well-funded field of aerospace research can push progress in biomedical gerontology, which suffers from severe underfunding, despite the serious economic difficulties caused by demographic aging of the population, ” says Franco Cortese, lead author scientific work, deputy director of the Biogerontology Research Foundation.

“This roadmap lays the foundation for enhancing human biology beyond our natural limitations to ensure not only long life expectancy and disease resistance, but also security during future space research,” said João Pedro de Magalhães ), co-author of the article, trustee of the Research Fund for Biogeronology.

Sooner or later we will have to do it - leave the Earth and go into deep space, says Dmitry Klokov, head of the radiobiology and health section of the Canadian nuclear laboratories, one of the authors of the scientific work. Such a trip outside the Earth's magnetosphere will cause great harm to the health of astronauts due to the effects of cosmic radiation. Therefore, it is better to start thinking about how we will cope with this task.

The scientific article was published on March 6, 2018 in the journal Oncotarget (doi: 10.18632 / oncotarget.24461).