WELCOME TO SPACE & HEALTH NEWS, our monthly briefing on opportunities and advances in deep space medicine and space healthcare. In this issue, we take a closer look at the threat posed by cosmic ionizing radiation to human space exploration, and what the industry is doing to mitigate it.
Ionizing radiation? Non-ionizing radiation? Cosmic radiation? Galactic radiation? For someone who is not a physicist, these terms tend to blend together. Yet when it comes to understanding the effects of radiation on human health, not all types of radiation are the same. So let’s first unpack these terms:
Non-ionizing radiation (low energy) is radiation that does not have enough energy to remove electrons from the material it passes through. Radio waves, microwaves, infrared, visible light, ultraviolet light – all are examples of non-ionizing radiation. Non-ionizing radiation can be damaging to live tissue, but we have ways to protect against it.
Ionizing radiation (high energy) consists of particles traveling at very high speed, that have enough energy to knock an electron out of its orbit, thus creating a more positively charged atom – an ion. Examples of ionizing radiation include alpha particles (helium atom nuclei moving at very high speeds), beta particles (high-speed electrons or positrons), gamma rays, x-rays, and galactic cosmic radiation (GCR). Ionizing radiation can pass through the hull of a spacecraft and through live tissue, and as it blasts its way through, it generates secondary particles that are propelled into motion by the primary radiation particles and are just as damaging.
Ionizing radiation particles are particularly dangerous to astronauts because they can pass through skin, depositing energy and damaging cells or DNA along the way. This damage can increase the risk for diseases later in life or cause radiation sickness during the mission. As physicist Marco Durante, PhD, Director of the Biophysics Department of the GSI Helmholtz Center (Darmstadt, Germany) and recognized expert in the fields of radiobiology and medical physics in charged particle therapy explains:
“One day in space is equivalent to the radiation received on Earth for a whole year.” (Marco Durante, PhD)Tweet
The particles associated with ionizing radiation are categorized into three main groups relating to the source of the radiation:
- Cosmic rays (Galactic Cosmic Radiation)
- Solar flare particles
- Trapped radiation belt particles (Van Allen Belts)
Of these, cosmic rays (Galactic Cosmic Radiation, or GCR) come from outside the solar system – primarily from within our Milky Way galaxy. In general, GCR is composed of the nuclei of atoms that have had their electrons stripped away and are traveling at nearly the speed of light. The GCR permeates interplanetary space and is comprised of roughly 85% hydrogen (protons), 14% helium, and about 1% high-energy and highly charged ions called HZE particles. The HZE particles have significant penetration power and a greater potential for radiation-induced damage. The GCR are the primary source of radiation aboard a spacecraft, and the most likely to imperil space missions. The GCR are affected by the Sun’s magnetic field, and their average intensity is highest during the period of minimum sunspots when the Sun’s magnetic field is weakest and less able to deflect them. On Earth, we are largely shielded from GCR because of our planet’s atmosphere and magnetic field, while the Moon is not shielded from GCR because it lacks a global magnetic field and atmosphere.
The second type of particles, solar flare particles, are produced as a result of explosions occurring near the Sun’s sunspots, which are regions of very strong magnetic fields. The number of sunspots waxes and wanes over an approx. 11-year cycle, and the frequency of occurrence of flares also varies with this solar activity cycle. Some of the solar energy particles accelerated by solar flares travel to the near-Earth interplanetary space where they can be detected by spacecraft and can even produce effects at the surface of the Earth.
The third, and lesser known, type of radiation particles are the particles trapped within the Van Allen Belts. The Van Allen Radiation Belts are two giant doughnut-shaped swaths of radiation, located in the inner region of Earth’s magnetosphere at an altitude of about 640 to 58,000 km (400 to 36,040 mi) above the surface. (Other belts are sometimes temporarily created). Most of the particles that form the belts are thought to come from solar wind (solar flare particles) and other particles from Galactic Cosmic Radiation. Earth’s magnetic field captures the high-energy particles and amasses them within the radiation belts, protecting the atmosphere and the Earth from their destructive power.
NASA’s Space Radiation Program Element (SRPE) : The major goal of NASA’s Space Radiation Program Element (SRPE) is to develop the knowledge base required by NASA to accurately predict and efficiently manage the radiation risk of human spaceflight. Current research sponsored by NASA seeks an understanding of DNA structural and functional changes caused by radiation, basic metabolic controls known to be modulated by radiation; genomic instability; changes to tissue structure; and “bystander” or non-targeted effects. The knowledge base has been built over time and continues to be augmented by a peer-reviewed, largely ground-based research program utilizing the NASA Space Radiation Laboratory at the Brookhaven National Laboratory (NSRL) and the Loma Linda University Proton Treatment Center.
At the NASA Space Radiation Laboratory at the Brookhaven National Laboratory (NSRL), for example, scientists can expose biological specimens – tissues, cells, and cell DNA – to beams of heavy ions simulating cosmic rays, to study the impacts and effects at the cellular level. Researchers can also use industrial materials as samples, studying their suitability for space suits and spacecraft shielding. Recent upgrades enable researchers to rapidly switch ion types and energy intensities. To support these improvements, software controls were added to permit smooth movement from target to target. This results in a more accurate testing environment for NASA researchers who are developing various types of shielding materials to protect astronauts from radiation.
GSI Helmholtz Centre for Heavy Ion Research: The European Space Agency has selected the GSI Accelerator Facility for its Investigations into Biological Effects of Radiation (IBER) program aimed at performing research into the biological effects of space radiation. This facility has already seen 36 experiments bombarding cells and materials with radiation to address the effects of space radiation. Further experiments will investigate radiation doses that astronauts could cope with while staying safe from cancer and other degenerative diseases during and after a mission.
European Space Agency (ESA) DOSIS-3D Study: One of the ESA’s contributions to the International Space Station is the Columbus laboratory, a research lab which provides internal payload accommodation for experiments in material science, fluid physics and life science. The ESA has carried out radiation monitoring experiments (DOSIS & DOSIS 3D) for the past ten years, to determine the doses of cosmic ionizing radiation absorbed by the ISS using a variety of active and passive radiation detector devices distributed throughout the ISS. These detectors – called dosimeters – help monitor the temporal and spatial distribution of radiation absorbed, and the data yielded feeds (together with the data collected by NASA and other partner agencies) into a 3D radiation map of the ISS.
NASA Human Research Program “Space Brain” Study: Funded by NASA’s Human Research Program under its “space brain” project, a study led by UC Irvine professor of radiation oncology Charles Limoli with participation from several academic institutions has concluded that exposure to complex radiation fields in space is “the primary risk to astronaut health as they venture from the protective magnetosphere of the Earth and beyond low Earth orbit en-route to distant worlds such as Mars.” Using the new, low dose-rate neutron irradiation capabilities available at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory (NSRL), researchers were able to demonstrate that realistic, low dose-rate exposures produce serious neurocognitive complications associated with impaired neurotransmission in rodents.
The recent experiments have shown losses in memory, recognition, cognitive flexibility, and anxiety and depression in the irradiated rodents, together with deficits in higher-order thinking associated with the capability to adapt to a changing environment. These experiments are consistent with the type of exposure astronauts would experience during travel, where they would be subject to large but infrequent solar particle events and to a steady shower of galactic cosmic radiation composed of highly energetic charged particles. As these findings emphasize, cosmic radiation poses multiple health and survivability risks, which will have to be addressed before long-distance space travel can become a reality.
Radiation-Shielding Vests: Cosmic radiation is rich in protons and neutrons, and one element that blocks both very well is hydrogen. Hydrogen is the most abundant element in the universe and is commonly found in compounds such as water and in materials such as polyethylene. Polyethylene, which is a type of plastic used for household items, is very high in hydrogen but doesn’t have the strength necessary to withstand heat and vibration and as a result cannot be used for large structures. However, for relatively small-size objects such as a radiation-shielding vest, polyethylene may be just the thing.
AstroRad is a radiation protection vest developed by StemRad, a start-up company sponsored by the Israel Space Agency for NASA’s Exploration Mission-1. Made of polyethylene to better block harmful protons, AstroRad will be tested on one of the twin female dummies that will be sent on the test flight.
The two female dummies will occupy the passenger seats during Orion’s first mission around the moon. Fitted with more than 5600 sensors, the dummies will measure the amount of radiation astronauts could be exposed to in future missions with unprecedented precision. The dummies simulate adult female torsos and are made up of 38 slices of tissue-equivalent plastics that mimic the varying density of bones, soft tissue and lungs.
Sensors have been fitted in the most radiation-sensitive areas of the body – lungs, stomach, uterus and bone marrow. While thousands of passive dosimeters will record the radiation dose from launch until return to Earth, a set of 16 active detectors will map the radiation dose both on the dummies’ skin and internal organs during flight. The only difference between the twin dummies is that one will be wearing a radiation protection vest, while the other will travel unprotected from cosmic radiation, to allow researchers to assess the effectiveness of the AstroRad vest.
Boron nitride nanotubes (BNNTs): A promising shielding material in development at NASA, the hydrogenated boron nitride nanotubes (BNNTs) are structurally similar to the better-known carbon nanotubes, and are shaped like cylinders of sub-micrometer level size made of carbon, boron, and nitrogen, with hydrogen interspersed throughout the empty spaces left in between the tubes. Both hydrogen and boron are excellent particle absorbers, and, as an added plus, the boron nitride nanotubes are much more thermally and chemically stable than the carbon nanotubes and can maintain their strength even at high temperatures.
Researchers at NASA have been able to spin BNNT into yarn that can be woven into the fabric for space suits, thus providing light-weight, flexible radiation shielding during space walks. BNNTs are still being studied and tested, but results so far indicate that they could play a key role in the development of radiation-shielding structures and materials for spacecraft, habitats and space suits.
3D-Printed Encasings for Moon Habitats: Skidmore, Owings & Merrill, the architectural firm known for designing the world’s tallest building, the Burj Khalifa in Dubai, is collaborating with the European Space Agency (ESA) and the Massachusetts Institute of Technology (MIT) on designing a moon colony. The so-called “Moon Village” would use sunlight for energy, and would be situated on the rim of the Shackleton Crater near the South Pole to receive continuous sunlight throughout the year while having ready-access to the ice reserves discovered near the Moon’s South Pole.
The settlement would comprise of clusters of inflatable pressurized modules that could easily expand to accommodate future growth. Each three- to four-story modular unit would include living quarters and workspaces and environmental control and life support systems, and would be encased in a shell of regolith (lunar soil) which would provide protection to extreme temperatures, dust, projectiles, and cosmic radiation. The walls of the shell would need to be considerably thick – about 10 ft. (3 meters) – to provide adequate shielding, and the firm is proposing to 3D-print the shell by extruding melted regolith through a nozzle like hot glue.
Since building on the Moon requires, first and foremost, dealing with the extremely abrasive regolith dust, the firm foresees that most of the construction and maintenance will be done by a robotic workforce.
TRISH: The Translational Research Institute for Space Health (TRISH), as part of their mission to reduce space radiation health risks, have announced the release of a new solicitation in January 2020 to procure industry support for:
- Determining whether human in vitro models could be effective for space radiation studies, and,
- Identifying effective countermeasures against high ionizing radiation – with an emphasis on non-pharmaceutical/nutritional countermeasure approaches.
Featured image: Earth observation of the space environment taken during a night pass by Dr. Kjell Lindgren of the Expedition 44 crew during Scott Kelly’s One-Year Mission aboard the International Space Station (ISS). An aurora with purple and SSRMS arm are visible.Image credit: NASA