Health threat from cosmic rays
Encyclopedia
The health threat from cosmic rays is the danger posed by galactic cosmic rays and solar energetic particles
to astronauts on interplanetary mission
s.
Galactic cosmic rays consist of high energy proton
s and other nuclei
with extrasolar origin. Solar energetic particles consist primarily of protons accelerated by the sun to high energies via proximity to solar flares and coronal mass ejections.
They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft
.
, due to the much larger flux of high-energy galactic cosmic rays (GCRs), along with radiation from solar proton event
s (SPEs) and the radiation belts.
Galactic cosmic rays create a continuous radiation dose throughout the solar system that increases during solar minimum and decreases during solar maximum (solar activity
). The inner and outer radiation belts are two regions of trapped particles from the solar wind that are later accelerated by dynamic interaction with the Earth's magnetic field. While always high, the radiation dose in these belts can increase dramatically during geomagnetic storms and substorm
s. Solar proton events are bursts of energetic protons accelerated by the sun. They occur relatively rarely and can produce extremely high radiation levels. Without thick shielding, SPEs are sufficiently strong to cause acute radiation poisoning
and death.
Life on the Earth's surface is protected from galactic cosmic rays by a number of factors:
As a result the energy input of GCRs to the atmosphere is negligible — about 10−9 of solar radiation - roughly the same as starlight.
Of the above factors, all but the first one apply to low earth orbit
craft, such as the Space Shuttle
and the International Space Station
. Average exposure on the ISS
is a rate of 150 mSv per year, though crew rotations are shorter than that. Astronauts on Apollo
and Skylab
missions received on average 1.2 mSv/day and 1.4 mSv/day respectively. Since the durations of the Apollo and Skylab missions were days and months respectively rather than years, the doses involved were smaller than what would occur, for example, on a crewed mission to Mars (unless far more shielding could be provided).
, high-energy cosmic rays can damage DNA
, increasing the risk of cancer
, cataract
s, neurological disorders
, and non-cancer mortality risks.
The Apollo astronauts reported seeing flashes
in their eyeballs, which may have been galactic cosmic rays, and there is some speculation that they may have experienced a higher incidence of cancer. However, the duration of the longest Apollo flights was less than two weeks, limiting the maximum exposure. There were only 24 such astronauts, making statistical analysis of the effects difficult.
The health threat depends on the flux, energy spectrum, and nuclear composition of the rays. The flux and energy spectrum depend on a variety of factors: short-term solar weather, long-term trends (such as an apparent increase since the 1950s), and position in the sun's magnetic field. These factors are incompletely understood.
The Mars Radiation Environment Experiment
(MARIE) was launched in 2001 in order to collect more data.
Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 milli-Sieverts (mSv) (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to ~500 to 1000 mSv. These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements
for Low Earth orbit
activities.
The quantitative biological effects of cosmic rays are poorly known, and are the subject of ongoing research. Several experiments, both in space and on Earth, are being carried out to evaluate the exact degree of danger.
Experiments at Brookhaven National Laboratory
's Booster accelerator revealed that the biological damage due to a given exposure is actually about half what was previously estimated: specifically, it turns out that low energy protons cause more damage than high energy ones. This is explained by the fact that slower particles have more time to interact with molecules in the body.
Several strategies are being studied for ameliorating the effects of this radiation hazard for planned human interplanetary spaceflight:
Special provisions would also be necessary to protect against a solar proton event (SPE), which could increase fluxes to levels that would kill a crew in hours or days rather than months or years. Potential mitigation strategies include providing a small habitable space behind a spacecraft's water supply or with particularly thick walls or providing an option to abort to the protective environment provided by the Earth's magnetosphere. The Apollo mission used a combination of both strategies. Upon receiving confirmation of an SPE, astronauts would move to the Command Module, which had thicker aluminum walls than the Lunar Module, then return to Earth. It was later determined from measurements taken by instruments flown on Apollo that the Command Module would have provided sufficient shielding to prevent significant crew harm.
None of these strategies currently provides a method of protection that would be known to be sufficient while conforming to likely limitations on the mass of the payload at present (~ $10000/kg) launch prices. Scientists such as University of Chicago professor emeritus Eugene Parker are not optimistic it can be solved any time soon. For passive mass shielding, the required amount could be too heavy to be affordably lifted into space without changes in economics (like hypothetical non-rocket spacelaunch
or usage of extraterrestrial resources) — many hundreds of metric tons for a reasonably-sized crew compartment. For instance, a NASA design study for an ambitious large spacestation envisioned 4 metric tons per square meter of shielding to drop radiation exposure to 2.5 mSv annually (+/- a factor of 2 uncertainty), less than the tens of mSv or more in some populated high natural background radiation areas on Earth, but the sheer mass for that level of mitigation was considered practical only because it involved first building a lunar mass driver
to launch material.
Several active shielding methods have been considered for lesser mass than passive mass shielding, but they remain in the realm of uncertain speculation at the present time. Since the segment of space radiation penetrating farthest through thick material shielding, deep in interplanetary space, is GeV-level positively charged nuclei, a repulsive positively charged electrostatic shield has been hypothesized, but issues include plasma instabilities and power needs for an accelerator constantly keeping the charge from being neutralized by deep-space electrons. A more common proposal is magnetic shielding using superconductors (or plasma currents), although, among other complications, if designing a relatively compact system, magnetic fields up to 10-20 Tesla could be required around a manned spacecraft higher than the several Tesla in MRI machines. The employment of magnetic structures which expose crew to such a high magnetic field may further complicate matters, though, since high-field (5 Tesla or more) MRIs have been noted to produce headaches and migraines in MRI patients, and high-duration exposure to such fields has not been studied. Opposing-electromagnet designs might cancel the field in the crew sections of the spacecraft, but such would raise mass. A hybrid of an electrostatic shield and a magnetic shield has also been conceived, charge neutral at large distances and theoretically much reducing the individual weaknesses of each, yet complex to design if doable.
Part of the uncertainty is that the effect of human exposure to galactic cosmic rays is poorly known in quantitative terms. NASA
has a Space Radiation Shielding Program to study the problem.
properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.
, interplanetary travel during solar maximum should minimize the average dose to astronauts.
Although the Forbush decrease
effect during Coronal mass ejection
s (CMEs) can temporarily lower the flux of galactic cosmic rays, the short duration of the effect (1–3 days) and the approximately 1% chance that a CME generates a dangerous solar proton event
limits the utility of timing missions to coincide with CMEs.
, with low inclination, will generally be below the inner belt.
The orbit of the Earth-Moon system Lagrange Points - takes them out of the protection of the Earth's magnetosphere
for approximately two-thirds of the time.
The orbits of Earth-Sun Lagrange Points and - are always outside of the protection of the Earth's magnetosphere.
Solar Energetic Particles
Solar Energetic Particles are high-energy particles coming from the Sun which had been first observed in the early 1940s. They consist of protons, electrons and heavy ions with energy ranging from a few tens of keV to GeV...
to astronauts on interplanetary mission
Interplanetary mission
An interplanetary mission is a voyage or trip through space involving more than one planet. This is an important distinction because it requires significantly more ΔV than do missions within a single planetary system....
s.
Galactic cosmic rays consist of high energy proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and other nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
with extrasolar origin. Solar energetic particles consist primarily of protons accelerated by the sun to high energies via proximity to solar flares and coronal mass ejections.
They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft
Human spaceflight
Human spaceflight is spaceflight with humans on the spacecraft. When a spacecraft is manned, it can be piloted directly, as opposed to machine or robotic space probes and remotely-controlled satellites....
.
The deep-space radiation environment
The radiation environment of deep space is very different from that on the Earth's surface or in low earth orbitLow Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
, due to the much larger flux of high-energy galactic cosmic rays (GCRs), along with radiation from solar proton event
Solar proton event
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the...
s (SPEs) and the radiation belts.
Galactic cosmic rays create a continuous radiation dose throughout the solar system that increases during solar minimum and decreases during solar maximum (solar activity
Solar variation
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...
). The inner and outer radiation belts are two regions of trapped particles from the solar wind that are later accelerated by dynamic interaction with the Earth's magnetic field. While always high, the radiation dose in these belts can increase dramatically during geomagnetic storms and substorm
Substorm
A substorm, sometimes referred to as a magnetospheric substorm or an auroral substorm, is a brief disturbance in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere and injected into the high latitude ionosphere. Visually, a substorm is seen as a sudden...
s. Solar proton events are bursts of energetic protons accelerated by the sun. They occur relatively rarely and can produce extremely high radiation levels. Without thick shielding, SPEs are sufficiently strong to cause acute radiation poisoning
Radiation poisoning
Acute radiation syndrome also known as radiation poisoning, radiation sickness or radiation toxicity, is a constellation of health effects which occur within several months of exposure to high amounts of ionizing radiation...
and death.
Life on the Earth's surface is protected from galactic cosmic rays by a number of factors:
- The Earth's atmosphere is opaque to primary cosmic rays with energies below about 1 GeV, so only secondary radiation can reach the surface. The secondary radiation is also attentuated by absorption in the atmosphere, as well as by radioactive decay in flight of some particles, such as muons. Particles entering from a direction close to the horizon are especially attenuated. At 15 km altitude, above not all yet most of the atmosphere's mass, radiation dose as an annual rate ranges from around 20 milli-SievertsSievertThe sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
(mSv) at the equator to 50 - 120 mSv at the poles, varying between solar maximum and minimum conditions, but the world's population rather receives an average of 0.4 mSv of cosmic radiation annually (separate from other sources of radiation exposure like inhaled radon) due to the tons per square meter of atmospheric mass shielding. - Except for the very highest energy galactic cosmic rays, the radius of gyration in the earth's magnetic fieldEarth's magnetic fieldEarth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
is small enough to ensure that they are deflected away from Earth. Missions beyond low earth orbit leave the protection of the geomagnetic field, and transit the Van Allen radiation beltVan Allen radiation beltThe Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...
s. Thus they may need to be shielded against exposure to cosmic rays, Van Allen radiation, or solar flareSolar flareA solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
s. The region between two to four earth radii lies between the two radiation belts and is sometimes referred to as the "safe zone". See the impact of the Van Allen belts on space travel for more information. - The interplanetary magnetic fieldInterplanetary Magnetic FieldThe interplanetary magnetic field is the term for the solar magnetic field carried by the solar wind among the planets of the Solar System....
, embedded in the solar windSolar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
, also deflects cosmic rays. As a result, cosmic ray fluxes within the heliopause are inversely correlated with the solar cycleSolar cycleThe solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...
.
As a result the energy input of GCRs to the atmosphere is negligible — about 10−9 of solar radiation - roughly the same as starlight.
Of the above factors, all but the first one apply to low earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
craft, such as the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
and the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
. Average exposure on the ISS
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
is a rate of 150 mSv per year, though crew rotations are shorter than that. Astronauts on Apollo
Project Apollo
The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...
and Skylab
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...
missions received on average 1.2 mSv/day and 1.4 mSv/day respectively. Since the durations of the Apollo and Skylab missions were days and months respectively rather than years, the doses involved were smaller than what would occur, for example, on a crewed mission to Mars (unless far more shielding could be provided).
Effects
Like other ionizing radiationIonizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
, high-energy cosmic rays can damage DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, increasing the risk of cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s, neurological disorders
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
, and non-cancer mortality risks.
The Apollo astronauts reported seeing flashes
Cosmic ray visual phenomena
Cosmic ray visual phenomena, also referred to as phosphenes or "light flashes", are spontaneous flashes of light visually perceived by astronauts outside the magnetosphere of the Earth, such as during the Apollo program. Researchers believe that cosmic rays are responsible for these flashes of...
in their eyeballs, which may have been galactic cosmic rays, and there is some speculation that they may have experienced a higher incidence of cancer. However, the duration of the longest Apollo flights was less than two weeks, limiting the maximum exposure. There were only 24 such astronauts, making statistical analysis of the effects difficult.
The health threat depends on the flux, energy spectrum, and nuclear composition of the rays. The flux and energy spectrum depend on a variety of factors: short-term solar weather, long-term trends (such as an apparent increase since the 1950s), and position in the sun's magnetic field. These factors are incompletely understood.
The Mars Radiation Environment Experiment
Mars Radiation Environment Experiment
The Martian Radiation Experiment, or MARIE was designed to measure the radiation environment of Mars using an energetic particle spectrometer as part of the science mission of the 2001 Mars Odyssey spacecraft...
(MARIE) was launched in 2001 in order to collect more data.
Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 milli-Sieverts (mSv) (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to ~500 to 1000 mSv. These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements
National Council on Radiation Protection and Measurements
The National Council on Radiation Protection and Measurements is a U.S. organization. It has a congressional charter under Title 36 of the United States Code, but this does not imply it has any sort of oversight or supervision from Congress; it is not a government entity.This text appears on the...
for Low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
activities.
The quantitative biological effects of cosmic rays are poorly known, and are the subject of ongoing research. Several experiments, both in space and on Earth, are being carried out to evaluate the exact degree of danger.
Experiments at Brookhaven National Laboratory
Brookhaven National Laboratory
Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
's Booster accelerator revealed that the biological damage due to a given exposure is actually about half what was previously estimated: specifically, it turns out that low energy protons cause more damage than high energy ones. This is explained by the fact that slower particles have more time to interact with molecules in the body.
Shielding
Material shielding can be effective against galactic cosmic rays, but thin shielding may situationally actually make the problem worse for some of the higher energy rays, because more shielding causes an increased amount of secondary radiation, although very (arguably impractically) thick shielding could counter such too. The aluminum walls of the ISS, for example, are believed to have a net beneficial effect. In interplanetary space, however, it is believed that thin aluminum shielding would have a negative net effect.Several strategies are being studied for ameliorating the effects of this radiation hazard for planned human interplanetary spaceflight:
- Spacecraft can be constructed out of hydrogen-rich plastics, rather than aluminum. Unfortunately, "[S]ome 'galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them,' cautions Frank Cucinotta, NASA's Chief Radiation Health Officer. 'All materials have this problem, including polyethylene.'"
- Material shielding has been considered:
- Liquid hydrogen, which would be brought along as fuel in any case, tends to give relatively good shielding, while producing relatively low levels of secondary radiation. Therefore, the fuel could be placed so as to act as a form of shielding around the crew. However, as fuel is consumed by the craft, the crew's shielding decreases.
- Water, which is necessary to sustain life, could also contribute to shielding. But it too is consumed during the journey unless waste products are utilized.
- Asteroids could serve to provide shielding.
- Magnetic deflection of charged radiation particles and/or electrostatic repulsion is a hypothetical alternative to pure conventional mass shielding under investigation. In theory, power requirements for the case of a 5 meter torus drop from an excessive 10 GW for a simple pure electrostatic shield (too discharged by space electrons) to a moderate 10 kW by using a hybrid design. However, such complex active shielding is untried, with workability and practicalities more uncertain than material shielding.
Special provisions would also be necessary to protect against a solar proton event (SPE), which could increase fluxes to levels that would kill a crew in hours or days rather than months or years. Potential mitigation strategies include providing a small habitable space behind a spacecraft's water supply or with particularly thick walls or providing an option to abort to the protective environment provided by the Earth's magnetosphere. The Apollo mission used a combination of both strategies. Upon receiving confirmation of an SPE, astronauts would move to the Command Module, which had thicker aluminum walls than the Lunar Module, then return to Earth. It was later determined from measurements taken by instruments flown on Apollo that the Command Module would have provided sufficient shielding to prevent significant crew harm.
None of these strategies currently provides a method of protection that would be known to be sufficient while conforming to likely limitations on the mass of the payload at present (~ $10000/kg) launch prices. Scientists such as University of Chicago professor emeritus Eugene Parker are not optimistic it can be solved any time soon. For passive mass shielding, the required amount could be too heavy to be affordably lifted into space without changes in economics (like hypothetical non-rocket spacelaunch
Non-rocket spacelaunch
Non-rocket space launch is a launch into space where some or all needed speed and altitude is provided by non-rocket means, rather than simply using conventional chemical rockets from the ground. A number of alternatives to rockets have been proposed...
or usage of extraterrestrial resources) — many hundreds of metric tons for a reasonably-sized crew compartment. For instance, a NASA design study for an ambitious large spacestation envisioned 4 metric tons per square meter of shielding to drop radiation exposure to 2.5 mSv annually (+/- a factor of 2 uncertainty), less than the tens of mSv or more in some populated high natural background radiation areas on Earth, but the sheer mass for that level of mitigation was considered practical only because it involved first building a lunar mass driver
Mass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential...
to launch material.
Several active shielding methods have been considered for lesser mass than passive mass shielding, but they remain in the realm of uncertain speculation at the present time. Since the segment of space radiation penetrating farthest through thick material shielding, deep in interplanetary space, is GeV-level positively charged nuclei, a repulsive positively charged electrostatic shield has been hypothesized, but issues include plasma instabilities and power needs for an accelerator constantly keeping the charge from being neutralized by deep-space electrons. A more common proposal is magnetic shielding using superconductors (or plasma currents), although, among other complications, if designing a relatively compact system, magnetic fields up to 10-20 Tesla could be required around a manned spacecraft higher than the several Tesla in MRI machines. The employment of magnetic structures which expose crew to such a high magnetic field may further complicate matters, though, since high-field (5 Tesla or more) MRIs have been noted to produce headaches and migraines in MRI patients, and high-duration exposure to such fields has not been studied. Opposing-electromagnet designs might cancel the field in the crew sections of the spacecraft, but such would raise mass. A hybrid of an electrostatic shield and a magnetic shield has also been conceived, charge neutral at large distances and theoretically much reducing the individual weaknesses of each, yet complex to design if doable.
Part of the uncertainty is that the effect of human exposure to galactic cosmic rays is poorly known in quantitative terms. NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
has a Space Radiation Shielding Program to study the problem.
Drugs
Another line of research is the development of drugs that mimic and/or enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are retinoids, which are vitamins with antioxidantAntioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.
Timing of missions
Due to the potential negative effects of astronaut exposure to cosmic rays, solar activity may play a role in future space travel. Because galactic cosmic ray fluxes within the solar system are lower during periods of strong solar activitySolar variation
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...
, interplanetary travel during solar maximum should minimize the average dose to astronauts.
Although the Forbush decrease
Forbush decrease
A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection . It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. The term Forbush decrease was named after the American...
effect during Coronal mass ejection
Coronal mass ejection
A coronal mass ejection is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space....
s (CMEs) can temporarily lower the flux of galactic cosmic rays, the short duration of the effect (1–3 days) and the approximately 1% chance that a CME generates a dangerous solar proton event
Solar proton event
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the...
limits the utility of timing missions to coincide with CMEs.
Orbital selection
Radiation dosage from the Earth's radiation belts is typically mitigated by selecting orbits that avoid the belts or pass through them relatively quickly. For example, a Low Earth orbitLow Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
, with low inclination, will generally be below the inner belt.
The orbit of the Earth-Moon system Lagrange Points - takes them out of the protection of the Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
for approximately two-thirds of the time.
The orbits of Earth-Sun Lagrange Points and - are always outside of the protection of the Earth's magnetosphere.
See also
- Background radiationBackground radiationBackground radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....
- HeliosphereHeliosphereThe heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
- MagnetosphereMagnetosphereA magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
- Proton: Exposure
- Solar flare: Hazards
- Solar proton eventSolar proton eventA Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the...
- Solar windSolar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
- Space medicine: What are the effects of space on the body
- Van Allen belt