Humans are delicate biological mechanisms capable of fantastic feats unlike those of any other beings we coexist with on Earth. We alone have achieved leaving our lovely home planet and venturing into space. I authored an accurate science fiction story about a crew of American astronauts who, in a future year, are sent on a mission to a planet in a neighboring solar system. The crew deals with space weather disrupting their flight, the physical challenges of moving through a variety of gravity fields, rocket mechanics, and the challenges and differences of a new planetary environment and atmosphere. The most emotionally difficult moment for the crew though in their long journey is when a crew member passes away while in transit between destinations due to increased exposure to radiation.
Radiation exposure is an extremely, if not the most, challenging issue for human astronauts to overcome when leaving the safety of Earth’s atmosphere. I will describe the sources of radiation in space, the physical effects of radiation exposure on humans, the plans to help protect astronauts on future missions, and the legacy of space radiation for past astronauts.
Generally, radiation is the emission of energy from a specific source in the form of electromagnetic waves or charged subatomic particles (11). For most living organisms, humans included, radiation is considered dangerous if it has the ability to ionize other molecules, as this damages the cells and molecules critical to survival. On the surface of the Earth, humans tend to experience radiation in the forms of alpha, beta, or gamma particles (8), or through ultraviolet waves. An alpha particle is a helium nucleus, consisting of two protons and two neutrons, a beta particle is an electron, and gamma particles are high energy and high speed energy packets (8).
Our atmosphere serves to protect humans from incoming space radiation by serving as buffer. The atmospheric gas molecules absorb the energy through photo dissociation, photo ionization, and scattering. These mechanisms prevent most of the incoming energy from outer space from ever reaching human civilization on ground level. However, any astronaut automatically exposes him or herself to more dangerous radiation by either leaving the atmosphere or going to an upper level of the atmosphere.
Space radiation is experienced in different forms than those on Earth. Galactic cosmic rays are protons with the ability to penetrate other molecules and heavy nuclei (3), while solar particle events are protons or ions with low to medium energy (3). Galactic cosmic rays have had all of their electrons stripped, originate outside of the Milky Way from events such as supernovas (6), and travel at close to the speed of light (7). Galactic cosmic rays, specifically the nuclei of heavier elements, have the capability to strike almost any object, human or metal spacecraft included, and break apart the atoms (7). The broken atoms then release subatomic particles, which act as radiation (7). Solar particle events are caused from solar storms, and are protons or ions with the ability to penetrate space suits, and occasionally even the physical spacecrafts (12).
Just on the International Space Station, the National Aeronautics and Space Administration, or NASA, reported astronauts received around ten times more radiation than the average human in the same measured time span (1). Although this statistic proves the risk to their personal health that astronauts have taken for the sake of science, a mission to another planet would require the astronauts leave the safety of Earth’s magnetic field (1), where the International Space Station resides. These astronauts would have even less of a buffer to protect them radiation.
NASA is currently in the throes of trying to plan an exploration and research mission to Mars involving human astronauts (1, 3). As part of the preparations for traveling to this far, but relatively close, destination, scientists have been researching what the radiation exposures would be for astronauts if they were to use the best of modern space travel technology (3).
Scientists have repeatedly found more exposure to radiation damages human cells, and leads to increased risks of cancer (1, 3). Radiation is capable of damaging the central nervous system (1), which consists of the brain and the spinal cord. Effects of radiation are seen on the central nervous system both acutely and on a long-term scale, with radiation damage effects ranging from damaged brain function, behavioral changes, and changed motor function (1). Radiation sickness can also result from high levels of exposure, with symptoms such as fatigue, vomiting, and a loss of appetite (1). Radiation can cause astronauts to develop degenerative tissue diseases, which are illnesses where the tissues suffer an irreversible loss of function (1). Additional effects of the increased space radiation exposure potentially faced by astronauts on long-term missions include gene expression changes, immune system activation, and changes in heart functions (9).
A specific experiment run to determine the effects of radiation is the Anomalous Long Term Effects in Astronauts’ Central Nervous System, or ALTEA (2). After analyzing reports of astronauts saying they saw flashes of light at night while on missions on the International Space Station, the Italian Space Agency decided to measure the cosmic radiation passing through crew members’ heads (2). It was hypothesized radioactive particles interacting with the eyes and brain caused the light flashes, so this experiment was to observe the effects of radiation on the central nervous system (2). The results for this study confirmed the trend of increased radiation exposure damaging human health, but the numbers related to the exposure are not related if the destination of the space mission of focus is outside the Earth’s magnetic field.
For a mission specifically to Mars, scientists have calculated astronauts would face a roughly 20% chance of dying from cancer in their lifetime after going on a 900 day round-trip (3). Life expectancy for astronauts would be reduced by about 15 years (3). The scientists who made these calculations also admitted it is hard to make actual predictions about radiation effects on the survival and health of astronauts as each individual is quite different healthwise (3). The varying health conditions of the astronauts could either amplify or minimize the effects of radiation exposure (3).
Any space mission outside of the Earth’s atmosphere will need highly advanced protection for all crew members to prevent illness and damage from space radiation. NASA is currently conducting research to help minimize radiation exposure from two approaches: finding biological countermeasures to help protect individual astronauts, and employing different shielding technology for the actual spacecraft which will be more effective in preventing radiation from the entering the inside (1).
Biological countermeasures are agents that work within the human body to protect and preserve human health, and mostly consist of advanced nutritional theories and better medications (3, 9). Although this research is ongoing, discoveries thus far have included that the addition of dietary antioxidants has beneficial health effects, such as preventing the loss of circulating white blood cells (9). Topically applied steroid cream can help with skin damage, and other drugs have been found to reduce radiation sickness symptoms such as vomiting (9).
Shielding technology is at the hands of rocket and material engineers. Radiation from solar particle events can almost be completely avoided through careful monitoring of the sun’s activity, and scheduling mission dates to avoid any large solar events (7).
Two options have been found for the protection of astronauts from galactic cosmic rays: the addition of traditional metal material to current rocket designs, or to find a building material that has better natural shielding capabilities (7). Adding volume for the sheer sake of protection is more expensive, as it would add mass to a ship that is already difficult to remove from the atmosphere (7).
Therefore, NASA is prioritizing efforts to research alternative materials to use for the rocket and the astronauts’ space suits (3, 7). The development of synthetic materials allows scientists to produce compounds which effectively block radiation particles through similarities in structure (7). The radiation particles cannot pass by atoms and molecules which mimic their shape and size. Many of the synthetic materials have a percent composition that leans heavily towards the element hydrogen due to its similar size to radiative protons and neutrons (7).
So far in history, the only humans to have traveled outside of the magnetosphere, where the International Space Station currently resides, are the Apollo lunar astronauts (4). The Apollo missions were conducted to land American astronauts on the moon, to explore the moon, and to compete with Russia during the Cold War for dominance in space achievements (10). Apollo lunar astronauts were shown in a recent study to have a mortality rate due to cardiovascular disease approximately four to five times greater than the mortality rates of astronauts who remained at least within the magnetosphere (4). Although this study was only released in 2016, and more research is sure to come, the results point to the dangers of humans going into deep space with the protocol and technology once previously used (4).
The last Apollo lunar mission left the moon on December 19th, 1972 (5), making it the 45th anniversary of a human leaving the magnetosphere this upcoming December. However, unlike during the era of the Apollo lunar missions, space radiation is a problem acknowledged by all scientists involved with planning future exploration missions (1, 3). As NASA prepares to take the next step in space exploration and send humans to the nearest potentially habitable planet, Mars, extensive research is proving the devastating and widespread effects of space radiation on the human body. Research is also continuing to allow scientists to discover methods, some simple and some much more technologically complex, that will help to protect future astronauts from the effects of space radiation exposure and enable the successful completion of long-term missions throughout our solar system and beyond.