Health threat from cosmic rays
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Health threats from cosmic rays are the dangers posed by
In October 2015, the NASA Office of Inspector General issued a health hazards report related to space exploration, including a human mission to Mars.[7][8]
The deep-space radiation environment
The radiation environment of deep space is different from that on the Earth's surface or in
Galactic cosmic rays (GCRs) consist of high energy
Microscopic energy deposition from highly ionizing particles consists of a core radiation track due to direct ionizations by the particle and low energy electrons produced in ionization, and a penumbra of higher energy electrons that may extend hundreds of microns from the particles path in tissue. The core track produces extremely large clusters of ionizations within a few
The radiation belts are within Earth's magnetosphere and do not occur in deep space, while organ dose equivalents on the International Space Station are dominated by GCR not trapped radiation. Microscopic energy deposition in cells and tissues is distinct for GCR compared to X-rays on Earth, leading to both qualitative and quantitative differences in biological effects, while there is no human epidemiology data for GCR for cancer and other fatal risks.
The
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 gigaelectron volt (GeV), so only secondary radiation can reach the surface. The secondary radiation is also attenuated by absorption in the atmosphere, as well as by radioactive decay in flight of some particles, such as muons. Particles entering from a direction far from the zenith are especially attenuated. The world's population receives an average of 0.4 millisieverts (mSv) of cosmic radiation annually (separate from other sources of radiation exposure like inhaled radon) due to atmospheric shielding. At 12 km altitude, above most of the atmosphere's protection, radiation as an annual rate rises to 20 mSv at the equator to 50–120 mSv at the poles, varying between solar maximum and minimum conditions.[10][11][12]
- Missions beyond low Earth orbit transit the Van Allen radiation belts. Thus they may need to be shielded against exposure to cosmic rays, Van Allen radiation, or solar flares. The region between two and four Earth radii lies between the two radiation belts and is sometimes referred to as the "safe zone".[13][14] See the implications of the Van Allen belts for space travel for more information.
- The heliopause are inversely correlated with the solar cycle.[15]
As a result, the energy input of GCRs to the atmosphere is negligible – about 10−9 of
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. Exposures on the ISS average 150 mSv per year, although frequent crew rotations minimize individual risk.[20] Astronauts on Skylab missions received on average 1.4 mSv/day.[20] Since the durations of the Skylab missions were days and months, respectively, rather than years, the doses involved were smaller than would be expected on future long-term missions such as to a near-Earth asteroid or to Mars[3] (unless far more shielding could be provided).
On 31 May 2013, NASA scientists reported that a possible human mission to Mars[3] may involve a great radiation risk based on the amount of energetic particle radiation detected by the radiation assessment detector (RAD) on the Mars Science Laboratory while traveling from the Earth to Mars in 2011–2012.[21][22][23] However, the absorbed dose and dose equivalent for a Mars mission were predicted in the early 1990s by Badhwar, Cucinotta, and others (see for example Badhwar, Cucinotta et al., Radiation Research vol. 138, 201–208, 1994) and the result of the MSL experiment are to a large extent consistent with these earlier predictions.
Human health effects
The potential acute and chronic health effects of space radiation, as with other ionizing radiation exposures, involve both direct damage to DNA, indirect effects due to generation of reactive oxygen species, and changes to the biochemistry of cells and tissues, which can alter gene transcription and the tissue microenvironment along with producing DNA mutations. Acute (or early radiation) effects result from high radiation doses, and these are most likely to occur after solar particle events (SPEs).[24] Likely chronic effects of space radiation exposure include both stochastic events such as radiation carcinogenesis[25] and deterministic degenerative tissue effects. To date, however, the only pathology associated with space radiation exposure is a higher risk for radiation cataract among the astronaut corps.[26][27]
The health threat depends on the flux, energy spectrum, and nuclear composition of the radiation. 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[28]), and position in the Sun's magnetic field. These factors are incompletely understood.[29][30] 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 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 roughly 500 to 1000 mSv.
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. Additionally, the impact of the space microgravity environment on DNA repair has in part confounded the interpretation of some results.[33] Experiments over the last 10 years have shown results both higher and lower than predicted by current quality factors used in radiation protection, indicating large uncertainties exist.
Experiments in 2007 at Brookhaven National Laboratory's NASA Space Radiation Laboratory (NSRL) suggest that biological damage due to a given exposure is actually about half what was previously estimated: specifically, it suggested that low energy protons cause more damage than high energy ones.[34] This was explained by the fact that slower particles have more time to interact with molecules in the body. This may be interpreted as an acceptable result for space travel as the cells affected end up with greater energy deposition and are more likely to die without proliferating into tumors. This is in contrast to the current dogma on radiation exposure to human cells which considers lower energy radiation of higher weighting factor for tumor formation. Relative biological effectiveness (RBE) depends on radiation type described by particle charge number, Z, and kinetic energy per amu, E, and varies with tumor type with limited experimental data suggesting leukemia's having the lowest RBE, liver tumors the highest RBE, and limited or no experimental data on RBE available for cancers that dominate human cancer risks including lung, stomach, breast, and bladder cancers. Studies of Harderian gland tumors in a single strain of female mice with several heavy ions have been made, however it is not clear how well the RBE for this tumor type represents the RBE for human cancers such as lung, stomach, breast and bladder cancers nor how RBE changes with sex and genetic background.
Part of the
Noting these limitations, a study published in
Central nervous system
Hypothetical early and late effects on the central nervous system are of great concern to NASA and an area of active current research interest. It is postulated short- and long-term effects of CNS exposure to galactic cosmic radiation are likely to pose significant neurological health risks to human long-term space travel.
In the above discussion dose equivalents is units of Sievert (Sv) are noted, however the Sv is a unit for comparing cancer risks for different types of ionizing radiation. For CNS effects absorbed doses in Gy are more useful, while the RBE for CNS effects is poorly understood. Furthermore, stating "hypothetical" risk is problematic, while space radiation CNS risk estimates have largely focused on early and late detriments to memory and cognition (e.g. Cucinotta, Alp, Sulzman, and Wang, Life Sciences in Space Research, 2014).
On 31 December 2012, a NASA-supported study reported that human spaceflight may harm the brains of astronauts and accelerate the onset of Alzheimer's disease.[48][49][50] This research is problematic due to many factors, inclusive of the intensity of which mice were exposed to radiation which far exceeds normal mission rates.
A review of CNS space radiobiology by Cucinotta, Alp, Sulzman, and Wang (Life Sciences in Space Research, 2014) summarizes research studies in small animals of changes to cognition and memory, neuro-inflammation, neuron morphology, and impaired neurogenesis in the hippocampus. Studies using simulated space radiation in small animals suggest temporary or long-term cognitive detriments could occur during a long-term space mission. Changes to neuron morphology in mouse hippocampus and pre-frontal cortex occur for heavy ions at low doses (<0.3 Gy). Studies in mice and rats of chronic neuro-inflammation and behavioral changes show variable results at low doses (~0.1 Gy or lower). Further research is needed to understand if such cognitive detriments induced by space radiation would occur in astronauts and whether they would negatively impact a Mars mission.
The cumulative heavy ion doses in space are low such that critical cells and cell components will receive only 0 or 1 particle traversal. The cumulative heavy ion dose for a Mars mission near solar minimum would be ~0.05 Gy and lower for missions at other times in the solar cycle. This suggests dose-rate effects will not occur for heavy ions as long as the total doses used in experimental studies in reasonably small (<~0.1 Gy). At larger doses (>~0.1 Gy) critical cells and cell components could receive more than one particle traversal, which is not reflective of the deep space environment for extended duration missions such as a mission to Mars. An alternative assumption would be if a tissue's micro-environment is modified by a long-range signaling effect or change to biochemistry, whereby a particle traversal to some cells modifies the response of other cells not traversed by particles. There is limited experimental evidence, especially for central nervous system effects, available to evaluate this alternative assumption.
Prevention
Spacecraft shielding
Material shielding can be effective against galactic cosmic rays, but thin shielding may actually make the problem worse for some of the higher energy rays, because more shielding causes an increased amount of secondary radiation, although thick shielding could counter such too.[51] The aluminium walls of the ISS, for example, are believed to produce a net reduction in radiation exposure. In interplanetary space, however, it is believed that thin aluminium shielding would give a net increase in radiation exposure but would gradually decrease as more shielding is added to capture generated secondary radiation.[52][53]
Studies of space radiation shielding should include tissue or water equivalent shielding along with the shielding material under study. This observation is readily understood by noting that the average tissue self-shielding of sensitive organs is about 10 cm, and that secondary radiation produced in tissue such as low energy protons, helium and heavy ions are of high linear energy transfer (LET) and make significant contributions (>25%) to the overall biological damage from GCR. Studies of aluminum, polyethylene, liquid hydrogen, or other shielding materials, will involve secondary radiation not reflective of secondary radiation produced in tissue, hence the need to include tissue equivalent shielding in studies of space radiation shielding effectiveness.
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 aluminium.[54]
- Material shielding has been considered:
- Liquid hydrogen, often used as fuel, 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.[55]
- Asteroids could serve to provide shielding.[56][57]
- Light active radiation shields based on the charged graphene against gamma rays, where the absorption parameters can be controlled by the negative charge accumulation.[58]
- 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 a 5-meter torus drop from an excessive 10
Special provisions would also be necessary to protect against a solar proton event, 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 aluminium 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.[citation needed]
None of these strategies currently provide a method of protection that would be known to be sufficient
Several active shielding methods have been considered that might be less massive than passive shielding, but they remain speculative.
Part of the uncertainty is that the effect of human exposure to galactic cosmic rays is poorly known in quantitative terms. The NASA Space Radiation Laboratory is currently studying the effects of radiation in living organisms as well as protective shielding.
Wearable radiation shielding
Apart from passive and active radiation shielding methods, which focus on protecting the spacecraft from harmful space radiation, there has been much interest in designing personalized radiation protective suits for astronauts. The reason behind choosing such methods of radiation shielding is that in passive shielding, adding a certain thickness to the spacecraft can increase the mass of the spacecraft by several thousands of kilograms.[63] This mass can surpass the launch constraints and costs several millions of dollars.
On the other hand, active radiation shielding methods is an emerging technology which is still far away in terms of testing and implementation. Even with the simultaneous use of active and passive shielding, wearable protective shielding may be useful, especially in reducing the health effects of SPEs, which generally are composed of particles that have a lower penetrating force than GCR particles.[64] The materials suggested for this type of protective equipment is often polyethylene or other hydrogen rich polymers.[65] Water has also been suggested as a shielding material. The limitation with wearable protective solutions is that they need to be ergonomically compatible with crew needs such as movement inside crew volume. One attempt at creating wearable protection for space radiation was done by the Italian Space Agency, where a garment was proposed that could be filled with recycled water on the signal of incoming SPE.[66]
A collaborative effort between the
Drugs and medicine
Another line of research is the development of drugs that enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are
Transhumanism
It has also been suggested that only through substantial improvements and modifications could the human body endure the conditions of space travel. While not constrained by basic laws of nature in the way technical solutions are, this is far beyond current science of medicine.
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 activity, interplanetary travel during solar maximum should minimize the average dose to astronauts.
Although the Forbush decrease effect during coronal mass ejections 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.
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 orbit, with low inclination, will generally be below the inner belt.
The orbits of the Earth-Moon system
The orbits of Earth-Sun system Lagrange Points L1 and L3 - L5 are always outside the protection of the Earth's magnetosphere.
See also
- Electromagnetic radiation and health
- Background radiation
- Effect of spaceflight on the human body
- Heliosphere
- Lagrange point colonization
- List of microorganisms tested in outer space
- List of solar storms
- Magnetosphere
- NASA Space Radiation Laboratory
- Proton: Human exposure
- Solar flare: Hazards
- Solar proton event
- Solar wind
- Space medicine
- Spaceflight osteopenia
- Van Allen belt
- Central nervous system effects from radiation exposure during spaceflight
References
- ^ a b Schimmerling, Walter. "The Space Radiation Environment: An Introduction" (PDF). The Health Risks of Extraterrestrial Environments. Universities Space Research Association Division of Space Life Sciences. Archived from the original (PDF) on 26 April 2012. Retrieved 5 December 2011.
- New York Times. Retrieved 27 January 2014.
- ^ a b c d Fong, MD, Kevin (12 February 2014). "The Strange, Deadly Effects Mars Would Have on Your Body". Wired. Retrieved 12 February 2014.
- ^ "Can People go to Mars?". science.nasa.gov. Archived from the original on 19 February 2004. Retrieved 2 April 2017.
- ^ Shiga, David (16 September 2009), "Too much radiation for astronauts to make it to Mars", New Scientist (2726)
- ISBN 9781426218644., we were exposed to a much greater flux of [galactic cosmic radiation].
Whenever the ISS flew through the South Atlantic Anomaly
- AP News. Retrieved 30 October 2015.
- ^ Staff (29 October 2015). "NASA's Efforts to Manage Health and Human Performance Risks for Space Exploration (IG-16-003)" (PDF). NASA. Retrieved 29 October 2015.
- ^ "Biomedical Results From Apollo - Radiation Protection and Instrumentation". lsda.jsc.nasa.gov. Archived from the original on 15 May 2013. Retrieved 2 April 2017.
- ^ Evaluation of the Cosmic Ray Exposure of Aircraft Crew
- ^ Sources and Effects of Ionizing Radiation, UNSCEAR 2008
- ^ Phillips, Tony (25 October 2013). "The Effects of Space Weather on Aviation". Science News. NASA.
- ^ "Earth's Radiation Belts with Safe Zone Orbit". Goddard Space Flight Center, NASA. 15 December 2004. Retrieved 27 April 2009.
- ^ Weintraub, Rachel A. "Earth's Safe Zone Became Hot Zone During Legendary Solar Storms". Goddard Space Flight Center, NASA. Retrieved 27 April 2009.
- S2CID 54025843.
- ^ NASA (2005). "Flashes in the Sky: Lightning Zaps Space Radiation Surrounding Earth". NASA. Retrieved 24 September 2007.
- ^ Robert Roy Britt (1999). "Lightning Interacts with Space, Electrons Rain Down". Space.com. Archived from the original on 12 August 2010. Retrieved 24 September 2007.
- ^ Demirkol, M. K.; Inan, Umran S.; Bell, T. F.; Kanekal, S. G.; Wilkinson, D. C. (1999). "Ionospheric effects of relativistic electron enhancement events". Geophysical Research Letters. 26 (23): 3557–3560. .
- ^ Jasper Kirkby; Cosmic Rays And Climate CERN-PH-EP/2008-005 26 March 2008
- ^ a b Space Radiation Organ Doses for Astronauts on Past and Future Missions Table 4
- ^ PMID 23723213.
- ^ S2CID 604569.
- ^ New York Times. Retrieved 31 May 2013.
- ^ Seed, Thomas. "Acute Effects" (PDF). The Health Effects of Extraterrestrial Environments. Universities Space Research Association, Division of Space Life Sciences. Archived from the original (PDF) on 26 April 2012. Retrieved 5 December 2011.
- PMID 16648048.
- S2CID 14387508.
- S2CID 9877997.
- ^ )
- ^ John Dudley Miller (November 2007). "Radiation Redux". Scientific American.
- ISBN 978-0-309-10264-3.
- ^ Study: Collateral Damage from Cosmic Rays Increases Cancer Risk for Mars Astronauts. University of Nevada, Las Vegas (UNLV). May 2017.
- PMID 28500351.
- PMID 28649636.
- S2CID 45921940.
- ^ Rettner, Rachael (5 July 2019). "Space Radiation Doesn't Seem to Be Causing Astronauts to Die from Cancer, Study Finds". LiveScience. Retrieved 7 May 2021.
- PMID 31273231. Retrieved 6 May 2021.
- PMID 9491253. Retrieved 8 May 2021.
- PMID 11541395.
- .
- S2CID 20017654.
- PMID 11537008.
- PMID 9650608.
- PMID 11541397.
- S2CID 43917453.
- PMID 1154020.
- PMID 11958207.
- S2CID 42284495.
- PMID 23300905.
- ^ Staff (1 January 2013). "Study Shows that Space Travel is Harmful to the Brain and Could Accelerate Onset of Alzheimer's". SpaceRef. Retrieved 7 January 2013.
- ^ Cowing, Keith (3 January 2013). "Important Research Results NASA Is Not Talking About (Update)". NASA Watch. Retrieved 7 January 2013.
- ^ a b NASA SP-413 Space Settlements: A Design Study. Appendix E Mass Shielding Retrieved 3 May 2011.
- ^ a b c d e G.Landis (1991). "Magnetic Radiation Shielding: An Idea Whose Time Has Returned?".
- ^ Rebecca Boyle (13 July 2010). "Juno Probe, Built to Study Jupiter's Radiation Belt, Gets A Titanium Suit of Interplanetary Armor". Popular Science.
- ^ "NASA - Plastic Spaceships". science.nasa.gov. Archived from the original on 23 March 2010. Retrieved 2 April 2017.
- ^ "Cosmic rays may prevent long-haul space travel". New Scientist. 1 August 2005. Retrieved 2 April 2017.
- ^ Morgan, P. (2011) "To Hitch a Ride to Mars, Just Flag Down an Asteroid" Discover magazine blog
- .
- S2CID 216229192.
- ^ PMID 16502610.
- ^ Simulations of Magnetic Shields for Spacecraft. Retrieved 3 May 2011.
- .
- ^ NASA SP-413 Space Settlements: A Design Study. Appendix D The Plasma Core Shield Retrieved 3 May 2011.
- S2CID 120839628.
- PMID 32355890.
- PMID 32718689.
- PMID 29198316.
- ^ Waterman, G., Milstein, O., Knight, L., Charles, J., Coderre, K., Posey, J., Semones, E. "AstroRad Radiation Protective Equipment Evaluations On Orion AND ISS", IAC-19,A1,5,5,x52629, 70 th International Astronautical Congress (IAC)
External links
- The Health Risks of Extraterrestrial Environments - an encyclopedic site
- Booster Accelerator at Brookhaven National Laboratory.
- Space Radiation Laboratory Archived 23 July 2012 at the Wayback Machine at BNL.
- The short film Radiation and Space Travel is available for free viewing and download at the Internet Archive.