The health threat of cosmic rays is the danger posed by galaxy cosmic rays (GCRs) and energetic sun particles for astronauts on interplanetary missions or missions that roam through the Van-Allen Belt or beyond the Earth's magnetosphere. They are one of the biggest barriers that stand in the way of plans for interplanetary travel by spacecraft crews, but the risk of radiation space radiation also occurs for missions in low Earth orbit such as the International Space Station (ISS).
In October 2015, the NASA Inspector General Office issued a health hazard report related to space exploration, including human mission to Mars.
Video Health threat from cosmic rays
Lingkungan radiasi angkasa-dalam
The radiation environment in space is much different from that on Earth's surface or in low Earth orbit, due to the larger flux of cosmic rays of high-energy galaxies (GCRs), along with radiation from solar proton events (SPE) and belt radiation.
Galactic cosmic rays (GCRs) consist of high energy protons (85%), helium (14%) and other high energy cores (HZE ions). Solar energy particles consist primarily of protons accelerated by the Sun for high energy through proximity to solar flares and coronal mass ejections. Heavy ions and low energy protons and helium particles are highly ionized forms of radiation, which produce different biological damage compared to X-rays and gamma rays. The accumulation of microscopic energy from high ion particles consists of core radiation paths due to direct ionization by particles and low-energy electrons generated in ionization, and higher energy-electron penumbras that can extend hundreds of microns from the path of particles in the network. The nuclear path produces an enormous ionisation cluster in a few nanometers, which is qualitatively different from the deposition of energy by X-rays and gamma rays; then human epidemiological data that exist only for this latter form of radiation is limited in predicting health risks from space radiation to astronauts.
But of course the radiation belt is inside the Earth's magnetosphere and does not occur in space, whereas the equivalent organ dosage at the International Space Station is dominated by non-trapped GCR radiation. The accumulation of microscopic energy in cells and tissues is different for GCR compared to X-rays on Earth that lead to qualitative and quantitative differences in biological effects, while there is no human epidemiological data for GCR for cancer and other fatal risks.
The solar cycle is a period of about 11 years from various solar activities including the maximum sun where solar wind is the strongest and minimum solar where the solar wind is the weakest. Galaxy cosmic rays create a continuous dose of radiation throughout the Solar System that increases during the minimum of the sun and decreases during the maximum of the sun (solar activity). The inner and outer radiation belts are two areas of particles trapped from the solar wind which are then accelerated by dynamic interactions with the Earth's magnetic field. Although always high, the dose of radiation in this belt can increase dramatically during storms and geomagnetic substances. Solar proton events are bursts of energetic protons that are accelerated by the Sun. They occur relatively rarely and can produce very high levels of radiation. Without a thick protector, SPE is strong enough to cause acute radiation poisoning and death.
Life on Earth's surface is protected from cosmic rays of galaxies by a number of factors:
- The Earth's atmosphere does not penetrate the primary cosmic light with energy below about 1 gigaelectron volt (GeV), so only secondary radiation can reach the surface. Secondary radiation is also attenuated by absorption in the atmosphere, as well as by radioactive decay in the flight of some particles, such as the muon. Particles entering from a distant direction of zenith are greatly attenuated. The world population receives an average of 0.4 millisieverts (mSv) of cosmic radiation each year (apart from other sources of radiation exposure such as radon inhalation) due to atmospheric shielding. At a height of 12 km, above most atmospheric protection, radiation as an annual rate rises to 20 mSv at the equator to 50-120 mSv at the poles, varying between maximum and minimum solar conditions.
- Missions outside Earth's low orbit carry Van Allen's radiation belt. Thus they may need to be protected against exposure to cosmic rays, Van Allen radiation, or solar flares. The region between the two and four radii of the Earth lies between two radiation belts and is sometimes referred to as a "safe zone". See the implications of the Van Allen belt for space travel for more information.
- Interplanetary magnetic fields, embedded in the solar wind, also deflect cosmic rays. As a result, cosmic ray flux in heliopause is inversely proportional to the solar cycle.
- Electromagnetic radiation created by lightning in a cloud just a few miles high can create a safe zone in the Van Allen radiation belt that surrounds the earth. This zone, known as the "Van Allen Belt slot", may be a safe place for satellites in medium Earth orbit (MEO), protecting them from intense radiation of the Sun.
As a result, GCR energy input into the atmosphere can be ignored - about 10 -9 solar radiation - more or less the same as starlight.
From the above factors, all but the first apply to the craft of low Earth orbit, such as Space Shuttle and International Space Station. Exposure to ISS averages 150 mSv per year, although crew rotation often minimizes individual risk. Astronauts on the Apollo and Skylab missions each received an average of 1.2 mSv/day and 1.4 mSv/day respectively. Since the Apollo and Skylab mission periods are days and months, respectively, not years, the dose involved is smaller than expected on future long-term missions such as near-Earth asteroids or to Mars (unless so many more shields can be provided).
On May 31, 2013, NASA scientists reported that the possibility of manned missions to Mars might involve a large risk of radiation based on the amount of energetic particle radiation detected by radiation detector detectors at Mars Science Laboratory while traveling from Earth to Mars in 2011-2012. However, the dose absorbed and the equivalent dose for Mars missions predicted in the early 1990s by Badhwar, Cucinotta, and others (see eg Badhwar, Cucinotta et al., Radiation Research vol. 138, 201-208, 1994) and the results of the experiments MSL is to a large extent consistent with this initial prediction.
Maps Health threat from cosmic rays
Human health effects
The potential for acute and chronic health effects of space radiation, such as exposure to other ionizing radiation, involves direct damage to DNA, the indirect effects of formation of reactive oxygen species, and cell and tissue biochemical changes, which can alter gene transcription. and micro-tissue environments together with producing DNA mutations. The acute effects (or initial radiation) result from high doses of radiation, and this is most likely to occur after the occurrence of solar particles (SPE). Possible chronic effects of exposure to space radiation include stochastic events such as radiation carcinogenesis and deterministic degenerative tissue effects. For now, however, the only pathology associated with exposure to space radiation is a higher risk for cataract radiation among astronauts.
The health threat depends on the flux, the energy spectrum, and the nuclear composition of the radiation. Flux and the energy spectrum depends on various factors: short-term solar weather, long-term trends (such as real increases since the 1950s), and position in the Sun's magnetic field. These factors are not fully understood. The Mars Radiation Environment Experiment (MARIE) was launched in 2001 to collect more data. The estimate is that humans who are not shielded in the interplanetary space will receive annually around 400 to 900 mSv (compared with 2.4 mSv on Earth) and that Mars missions (12 months in flight and 18 months on Mars) may expose astronauts who are protected to about 500 to 1000 mSv. This dose is approaching the 1 to 4 Sv career range recommended by the National Council for Radiation Protection and Measurement (NCRP) for low Earth orbit activities in 1989, and a newer NCRP recommendation from 0.5 to 2 Sv in 2000 based on updated information about dose to risk the conversion factor. Dose limits depend on age at exposure and sex due to differences in susceptibility to age, additional risk of breast and ovarian cancer for women, and variability of cancer risk such as lung cancer between men and women.
The quantitative biological effects of cosmic rays are less well known, and are the subject of ongoing research. Several experiments, both in space and on Earth, are underway to evaluate the exact degree of danger. In addition, the environmental impact of space mikrogravitasi on DNA repair has confused the interpretation of some results. Experiments over the past 10 years have shown results higher and lower than those predicted by the current quality factor used in radiation protection, indicating considerable uncertainty. A 2007 experiment at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory showed that the biological damage caused by certain exposures was actually about half the previous estimate: specifically, low energy protons cause more damage than high energy. This is explained by the fact that slower particles have more time to interact with the molecules in the body. This can be interpreted as an acceptable result for space travel because the affected cells end up with a larger energy deposition and are more likely to die without proliferating into tumors. This is in contrast to the current dogma in radiation exposure in human cells that considers lower energy radiation from higher weighting factors for tumor formation. The relative biological effectiveness (RBE) depends on the type of radiation described by the particle charge number, Z, and the kinetic energy per amu, E, and varies with the type of tumor with limited experimental data showing leukemia has the lowest RBE, the highest RBE liver tumor, and is limited. or no experimental data on RBE available for cancer that dominates the risk of human cancers including lung, stomach, breast, and bladder cancer. The study of Harderian gland tumors in a single female strain with some heavy ions has been made, but it is unclear how well RBE for this type of tumor represents RBE for human cancers such as lung, stomach, breast and bladder cancer as well as how RBE changes with sex and genetic background.
Part of ISS's long-term mission is to determine the health impact of cosmic rays for a year spent on the International Space Station.
However, the sample size for accurately predicting health risks directly from crew observations for the risk of concern (cancer, cataract, cognitive and memory changes, late CNS risk, circulatory disease, etc.) is large (typically & gt; 10 people) and need to involve long post-mission observation time (& gt; 10 years). It would be difficult for a sufficient number of astronauts to occupy the ISS and for the mission to continue long enough to make an impact on risk prediction for late effects due to statistical limitations. Therefore the need for ground-based research to predict cosmic ray health risks. In addition, radiation safety requirements require that risks should be adequately understood before astronauts pose significant risks, and methods are developed to reduce risk if necessary.
In September 2017, NASA reported radiation levels on the surface of the Mars planet while replicated, and associated with aurora 25-times brighter than previously observed, due to massive and unpredictable sun-storms in the middle of the month..
Central nervous system
The initial hypothesis and late effects on the central nervous system is a major concern for NASA and the current active field of interest in research. Postulated short-term and long-term effects of CNS exposure to galactic cosmic radiation are likely to pose significant neurological health risks to long-term human space travel. Estimates show considerable exposure to high energy heavy ions (HZEs) as well as protons and secondary radiation during Mars or a prolonged Lunar mission with an approximate effective dose of whole body ranging from 0.17 to greater than 1.0 Sv. Given the high linear energy transfer potential of such particles, most of the cells exposed to HZE radiation tend to die. Based on heavy ion flu calculations during space flight as well as experimental cell models, as many as 5% astronaut cells may be killed during the mission. With respect to the cells in critical brain regions, as many as 13% of these cells can be passed at least once by iron ions during Mars's three-year mission. Some Apollo astronauts reported seeing the light blink, although the exact biological mechanism responsible is not clear. Possible pathways include heavy ion interactions with the retinal photoreceptor and Cherenkov radiation resulting from the interaction of particles in vitreous humor. This phenomenon has been replicated on Earth by scientists at various institutions. Because the duration of the longest Apollo flight is less than two weeks, the astronauts have limited cumulative exposure and a corresponding low risk for radiation carcinogenesis. In addition, there are only 24 such astronauts, making statistical analysis of any potential health effects problematic.
In the above discussion the equivalent dose is the Sievert (Sv) unit recorded, but Sv is the unit to compare cancer risk for different types of ionizing radiation. For the effects of CNS the doses absorbed in Gy are more useful, whereas RBE for CNS effects is poorly understood. Furthermore, it states "hypothetical" risk issues, while CNS space radiation risk estimates are mostly focused on the beginning and end of loss to memory and cognition (eg Cucinotta, Alp, Sulzman, and Wang, Life Sciences in Space Research, 2014).
As of December 31, 2012, a NASA-supported study reported that manned space could harm astronaut's brain and accelerate the onset of Alzheimer's disease. This study is problematic because of many factors, including the intensity of mice that are exposed to radiation that far exceeds the normal mission level.
The review of CNS space radiobiology by Cucinotta, Alp, Sulzman, and Wang (Life Sciences in Space Research, 2014) summarizes research studies on small animals of cognition and memory changes, neuronal inflammation, neuron morphology, and neurogenesis disorders in the hippocampus. Studies using simulated space radiation in small animals show temporary or long-term cognitive impairment can occur during long-term space missions. Neuronal morphological changes in the hippocampus of the mouse and pre-frontal cortex occur for low-dose (or 0.3 Gy) heavy ions. Studies in rats and mice from chronic neuro-inflammatory and behavioral changes showed variable results at low doses (~ 0.1 Gy or lower). Further research is needed to understand whether cognitive impairment caused by space radiation will occur in astronauts and whether they will negatively impact Mars's mission.
The dose of cumulative heavy ions in the space is so low that the critical cells and cell components will only accept 0 or 1 traversal particles. The dose of cumulative heavy ions for Mars missions near the minimum sun is ~ 0.05 Gy and lower for missions at other times in the solar cycle. This suggests dose-dose effects will not occur for heavy ions during the total dose used in the experimental study in small enough (& lt; ~ 0.1 Gy). At larger doses (& gt ~ 0.1 Gy) critical cells and cell components can receive more than one traversal particle, which does not reflect the inner space environment for extended duration missions such as missions to Mars. An alternative assumption is that if the micro-tissue environment is modified by the effects of long-distance signals or transforms into biochemistry, where particles passing through multiple cells modify other cell responses not passed by the particles. There is limited experimental evidence, especially for central nervous system effects, available to evaluate these alternative assumptions.
Mitigation
Protect
Shielding materials can be effective against galactic cosmic rays, but thin shields can actually make matters worse for some higher energy rays, as more shields lead to an increase in the amount of secondary radiation, even though a thick shield can fight like that too. The ISS aluminum wall, for example, is believed to result in a net reduction in radiation exposure. In interplanetary space, however, it is believed that a thin aluminum protector will provide a net increase in radiation exposure but will gradually decrease as more shields are added to capture the resulting secondary radiation.
The study of space radiation shields should include a shield of tissue or water sheath together with the shield material under study. This observation is easily understood by noting that the mean tissue that protects itself from sensitive organs is about 10 cm, and that secondary radiation produced in tissues such as low energy protons, helium and heavy ions is high LET and makes a significant contribution ( & gt; 25%) for overall biological damage from GCR. Studies of aluminum, polyethylene, liquid hydrogen, or other shielding materials, will involve secondary radiation that does not reflect the secondary radiation produced in the tissue, hence the need to include a network equivalent shield in the study of the effectiveness of spaceborne shielding.
Several strategies are being studied to improve the effects of these radiation hazards for the planned interplanetary human spaceflight:
- Spaceships can be built from hydrogen-rich plastics, not aluminum.
- Protective material has been considered:
- Liquid hydrogen, which will be carried as fuel in any case, tends to provide adequate protection, while producing relatively low levels of secondary radiation. Therefore, the fuel can be placed so that it acts as a form of shield around the crew. However, due to the fuel consumed by the aircraft, the crew's shield is reduced.
- Water, which is necessary to sustain life, can also contribute to protecting. But it is also consumed during the trip unless the waste product is used.
- Asteroids can serve to provide protection.
- The magnetic deflection of charged charged particle and/or electrostatic repellents is a hypothetical alternative to the conventional mass shield convention under investigation. Theoretically, the power requirement for the case of a 5 meter drop of torus from 10 GW is excessive for simple pure electrostatic shields (too disposed of by space electrons) up to 10 kilowatts moderate (kW) using a hybrid design. However, such complex active shields have not been tried, with workability and practicality more uncertain than material shields.
Special provisions are also required to protect against the events of solar protons, which can increase the flux to levels that will kill the crew in a few hours or days rather than months or years. Potential mitigation strategies include providing a small habitable space behind the spacecraft's water supply or with very thick walls or providing an option to cancel into the protective environments provided by the Earth's magnetosphere. The Apollo mission uses a combination of both strategies. After receiving SPE confirmation, the astronaut will move to Command Module, which has thicker aluminum wall than Lunar Module, then back to Earth. It was then determined from the measurements taken by instruments flown in Apollo that the Command Module would provide sufficient protection to prevent significant crew hazards.
None of these strategies currently provides enough protection methods that will be known while adjusting for possible limitations on the current charge mass (about $ 10,000/kg) launch price. Scientists like professors at the University of Chicago Eugene Parker are not optimistic it can be solved in the near future. For passive mass shields, the required amount can be too heavy to be lifted into space without changes in the economy (such as hypothetical non-rocket spacelaunch or use of space resources) - hundreds of metric tons for a sufficient-size crew compartment. For example, the NASA design study for large ambitious spacestation envisions 4 metric tons per square meter of shield to drop radiation exposure to 2.5 mSv each year (Ã, Â ± 2 factor uncertainty), less than tens of millisieverts or more in some inhabited area of ​​background radiation high natural rear on Earth, but a large mass for mitigation rate is considered practical simply because it involves first building a mass moon driver for launching material.
Some active shielding methods have been considered that may be less massive than passive shields, but they remain speculative. Because the type of radiation that penetrates furthest through thick material shields, deep in the interplanetary space, is a positively charged nucleus of GeV, a disgusting electrostatic field has been proposed, but it has problems including plasma instability and power required for accelerators that constantly keep the charge from being neutralized by the celestial electrons. A more general proposal is a magnetic shield produced by a superconductor (or plasma stream). Among the difficulties with this proposal is that, for a compact system, up to 10-20 teslas magnetic fields can be required around manned spacecraft, higher than some tests in an MRI machine. Such high fields can cause headaches and migraines in MRI patients, and long-term exposure to such areas has not been investigated. The opposite electromagnet design may cancel the field in the space crew section, but it will require more mass. It is also possible to use a combination of magnetic field with an electrostatic field, with a spacecraft having a zero total charge. Hybrid design will theoretically fix the problem, but it will be complicated and may not be feasible.
Part of the uncertainty is that the effects of human exposure to galaxy cosmic rays are less known quantitatively. The NASA Space Radiation Laboratory is currently studying the effects of radiation on living organisms and protective masks.
Drugs
Another line of research is the development of drugs that increase the body's natural capacity to repair damage caused by radiation. Some of the drugs under consideration are retinoids, which are vitamins with antioxidant properties, and molecules that inhibit cell division, allowing time on the body to repair damage before harmful mutations can be duplicated.
Mission time
Due to the potential negative effects of astronaut exposure to cosmic rays, solar activity can play a role in space travel in the future. Because cosmic galaxy cosmic rays in the Solar System are lower during periods of strong solar activity, interplanetary travel during the maximum sun should minimize the average dose for astronauts.
Although the effect of Forbush reduction during coronal mass release can decrease the cosmic ray flux of the galaxy, the short duration of the effects (1-3 days) and about 1% chance that CME produces a dangerous solar proton event limits the usefulness of the time mission to coincide with CME.
Orbital Selection
The radiation dose of the Earth's radiation belt is usually reduced by choosing an orbit that avoids the belt or passes it relatively quickly. For example, a low Earth orbit, with a low tendency, will generally be under the inner belt.
The Lagrange system's Orbit-Moon system shows L 2 - L 5 to bring them out of Earth's magnetosphere protection for about two thirds of time.
The Earth-Sun Orbit Lagrange Points L
See also
References
External links
Source of the article : Wikipedia
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