How Space Radiation Threatens Lunar Exploration

This article was originally published on Supercluster, a website dedicated to telling humanity's greatest outer space stories.

NASA is preparing to return astronauts to the lunar surface. And this time with more ambitious goals.

Those missions, which had a successful kickoff with Artemis-1, will establish the groundwork for months-long human habitation on the Lunar surface. Proposed base camps will present unique opportunities to test technology, unravel scientific secrets about the Moon's past and present, search for the presence of water, and more.

But before our sci-fi Moonbase becomes a reality, astronauts must perform a variety of tasks on the lunar surface, including site exploration, construction, and resource extraction. For all of these tasks and the operations in between, space radiation poses a threat to the space farers performing them.

Between 1968 and 1972, the Apollo missions carried a dozen astronauts to the Moon and back. But all of these missions were brief — the longest lasted only about 12 days. We’ve been there before, but the effects of space radiation are still little-known, and understanding their effects on the human body is vital for months-long missions.

A Fusillade of Powerful Particles

Earth's magnetic field and atmosphere shield it from dangerous radiation and safeguard life on the planet. The outer worlds that humanity has targeted are incredibly hostile by comparison. Even an hour without adequate protection could be lethal, as charged particles pass constantly through human skin. This paints a bleak picture for future exploration.

Even our Moon is a hazardous, desolate place — devoid of atmosphere, and lacking protection from a constant rain of radiation emitted by our Sun. Apart from the Sun, astronauts are also subjected to other sources of radiation on the Moon.

First to consider are the galactic cosmic rays (GCR) released by exploding stars out in deep space. And then there are particles created in the lunar soil, as a result of the interactions between solar energetic particles from the Sun and galactic cosmic rays. Solar particles are less energetic than galactic cosmic rays, “but when there is a solar particle event, then their flux can be much higher than that of galactic cosmic rays,” said Robert F. Wimmer-Schweingrube from the University of Kiel in Germany.

In the annals of human spaceflight, August 1972 is unforgettable. A series of intense solar flares exploded intermittently for more than a week. A solar flare is an outburst of charged particles from the Sun’s turbulent surface. There are five classes: A, B, C, M, and X, ranging in size from the smallest to the most dangerous. The intense solar storm of 1972, which was an X-class flare, originated from a sunspot named MR 11976.

The crew of Apollo 16 had landed on Earth in April, and the final Apollo 17 trip was scheduled for December. A potential disaster was narrowly avoided. Astronauts stepping onto the lunar surface would have died from radiation, and the storm's fury was felt on Earth as well — it disrupted the energy and communication grids in several parts of North America.

Dangerous Passage

Space radiation poses a concern not just on the surface, but on the round-trip journey. Around Earth, there are hazardous radiation rings, the Van Allen Belts, consisting of highly charged particles captured by the planet’s magnetic fields. The more time spent passing through these belts, the greater the risk of radiation poisoning.

There are two radiation rings. The first one starts at a height of 600 km and extends to 6,000 km. The second deadly ring stretches from between 10,000 and 65,000 kilometers above Earth. The intensity of the latter only gets worse as solar storms rage. Thankfully the Space Station remains untouched and shielded in low-Earth Orbit at 230 miles, but though our lunar spacecraft are designed to shield their crew, the flood of lethal particles can still seep inside.

So how did earlier Apollo missions manage to navigate this challenging area? Speed. The past Apollo missions followed a tight trajectory to avoid the most radioactive part of the belts and traversed at a high speed. Scientists determined the optimal speed for crew-carrying spacecraft to be roughly 25,000 km/h with a total transit period of 68.1 minutes.

Radioactive Baker’s Yeast

In this new space age, the dread of radiation still looms. And new answers are needed. The Artemis-1 mission carried mannequins and other biological experiments to study exposure.

Yeast cells flown on the mission require little upkeep for factors like water, temperature, or nutrients. Yeast acts as a model organism in DNA damage studies, and its response has been well studied. A near-perfect analog for human genes is the baker's yeast (Saccharomyces cerevisiae). This single-celled microorganism can give information on how living organisms cope with dangerous cosmic radiation.

The experiment tries to unravel complicated space radiation-related puzzles. What effects do charged particles have on DNA, cells, and tissues in humans? What degree of DNA damage is there? Which genes were radiation-resistant?

Peter Guida, a biologist with NASA explains in a statement: “DNA bases (adenine, guanine, cytosine, and thymine) can also be knocked out. The cell will make an attempt to repair these damages. Sometimes it’s effective and sometimes it’s not, and sometimes it can be misrepaired. Genes that have been misrepaired can become mutations, and the accumulation of these mutations over time can potentially lead to cancer.”

To study this accumulation, a collection of bar-coded yeast cells traveled to the Moon and back. Yeast cells were supposed to grow and divide throughout the mission after the samples have been launched to space and activated remotely by the addition of water.

With Orion’s return to Earth, scientists from the University of British Columbia will retrieve the samples to carry out a laboratory study. Once the genes have been identified, scientists could use this information to develop drugs or treatments that can tolerate radiation shocks and reduce the likelihood of adverse health effects.

Meanwhile, another deep-space biology experiment will carry more yeast samples to orbit around the Sun for about six to nine months. BioSentinel — a shoebox-sized CubeSat — which also hitched a ride on Artemis-1. A new biosensor is used in the experiment to examine how living yeast cells respond and adapt to prolonged exposure. Scientists will track the experiment in real time via NASA’s Deep Space Network.

How Much is Too Much?

The 1972 event is sometimes used as a reference point to comprehend the "what ifs" of sending astronauts to the Moon. The astronauts would have experienced radiation sickness, at minimum, if they had been exposed to those lethal radiation doses.

According to NASA, the standard radiation dose for a person on Earth is about 0.0036 Sv/ year (0.36 rad). The Apollo astronauts received an average radiation dose on the skin of 0.38 rad — equivalent to two head CT scans. Overall, Apollo 14 received the skin dose of 1.14 rad, which was the highest. All this during missions not longer than 12 days.

The daily radiation dose on the surface of the Moon could be substantially higher during a longer mission, and it is impossible to quantify from Earth. To find out how high, the Lunar Lander Neutron and Dosimetry (LND), onboard the Chinese lunar lander Chang’E 4, traveled to the Moon. LND recorded the first-ever measurements of radiation levels on the Moon.

According to estimates, astronauts in a spacesuit would be exposed to around 60 microsieverts of radiation every hour. Overall, the radiation level exposure could shoot up to 150 times higher than on Earth.

Have you ever wondered about the acceptable space radiation exposure limit for humans? "We don't really know," according to co-author of the LND study, Dr Wimmer. “We don't yet have experience with deep space radiation, there are different ways that radiation affects our body and different parts of our body.”

Female Body More Vulnerable

Without any protection, astronauts are more likely to have both acute and chronic health problems, such as cataracts and heart diseases. Additionally, they may suffer from short-term radiation illness, and risks of cancer development in long-term.

Based on a person's age and gender, NASA has estimated career exposure limits. Presumably, early-career astronauts could have higher health risks in their later years due to radiation exposure. And studies have suggested that females could be more vulnerable to radiation.

“Females have a much higher risk of cancer from radiation due to the additional risks to the breast (one of the highest), ovarian, and uterine cancers. For males, the risk of prostate cancer appears from radiation exposure, however, it has a low mortality probability,” said Professor Francis Cucinotta, an expert in radiation biology from the University of Nevada in Las Vegas, in an email response to Supercluster.

That’s why NASA has flown an experiment to understand the implications of radiation on the female body, for the first time. As NASA works to send a female astronaut to space, this experiment is crucial.

The Artemis-1 mannequins — named Zohra and Helga — have been designed to measure and test the effect of radiation on internal organs. The damage encountered by internal organs depends on energy absorbed, particle density, and time spent outside the protective habitat.

34 detectors and more than 5,000 sensors were placed all over these mannequins to measure radiation levels during Orion's flight. The mannequins, which are made of epoxy resins, replicate an adult female's bones, soft tissues, and organs.

One of the mannequins wore AstroRad, a brand-new radiation vest. The vest's main purpose is to protect sensitive organs against solar particle events. Through this test flight, scientists will learn more about the belt's efficiency as well as how it protects internal organs by contrasting the two subjects. The experiment is known as the Matroshka AstroRad Radiation Experiment (MARE). Radiation sensors incorporated into Orion monitored radiation levels throughout the flight, especially in areas where they are at their highest.

Research from this experiment is expected to be published soon.

Lunar Shielding

Artemis’ Orion has been designed with an array of features to protect both humans and hardware in a worst-case scenario. A stowage bag or other material found onboard might be used to construct a temporary radiation shelter inside the spacecraft.

As per NASA, the crew might need to stay in this storm shelter for at least a day. Extreme space weather would not prevent the crew from carrying out "critical mission activities," though, thanks to the protective radiation vests.

During periods of severe solar activity, astronauts might potentially construct a shielded habitat using local resources, such as lunar soil, dirt, and rocks. For instance, walls about one meter thick can be built by 3D printing building blocks from lunar dust (regolith).

“Another way to construct a shielded habitat is to simply "pile dirt" onto a solid construction that can support its weight,” suggests Dr. Wimmer. In addition, it would be useful to forecast space weather and issue early storm warnings for stays longer than a month.

The first Artemis mission is considered an initial success as we await published results from various experiments. If things go well with the next few crewed Artemis missions, NASA will soon be preparing for humanity’s next radiation challenge: Mars.