Every job in deep space is fraught with danger. Hardware failure during launch, equipment malfunctioning far from Earth, or a small space rock hitting the vehicle are all scenarios that astronauts will train for.
As humans embark on Artemis II, their first visit to the Moon in more than 50 years, one constant threat they face is solar radiation.
Strong bursts of radiation from the Sun, known as solar particle events, can endanger the lives of astronauts, especially those going beyond low Earth orbit (LEO). During these events, high speed, charged particles flow from the Sun into space.
Exposure to these particles can lead to radiation sickness or, in the worst cases, death. In space stations and other vehicles that travel in LEO, scientists get the highest protection from the magnetic sphere that surrounds the Earth (magnetosphere).
But in the interplanetary space, where Artemis II is heading, people are exposed to a lot of sunlight.
The Sun’s magnetic activity fluctuates in a cycle that lasts about 11 years. During this cycle, sunspots (areas of reduced heat caused by strong magnetic fields) can cause volcanic eruptions known as flares, as well as solar particle events. These rise and fall regularly with the solar cycle.
The current solar cycle reached its maximum, when the Sun is generally at its most active, in 2024 and is now slowly decreasing towards its minimum, when the Sun is at its quietest. The current cycle is due at least in 2031.
Not all solar cycles are the same and now there is no differentiation according to activity, like the previous cycle that reached the top in 2014. However, recently, the Sun woke up from its slumber.
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On 11 November 2025, a large solar particle event increased global radiation by around 145% for two hours, as measured by the University of Surrey’s neutron probe at the Met Office station in Lerwick, Shetland.
This has also been detected by the University of Surrey’s SAIRA (Smart Atmospheric Ionizing Radiation) monitors installed on two trans-Atlantic flights and rapid flights of weather balloons in Lerwick, Cambourne and near Utrecht in the Netherlands.
Work is underway to unravel this complex phenomenon to determine that radiation is increasing worldwide using the University of Surrey MAIRE (Model for Atmospheric Ionizing Radiation Effects) computer model. This measures radiation levels at high altitudes for normal atmospheric conditions, as well as enhanced radiation events caused by increased solar activity.
Three immediate research papers are presented to describe radiation monitors and their calibration, summarize pilot data and compare data with existing models.
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The line is close
The solar phase event on November 11, 2025 tells us that, no matter what the odds are, the Sun can always surprise us.
To emphasize the importance of such events for deep space missions, let’s go back in time to 1972. At that time, the Sun was waning in the same way in its 11-year cycle as we are today. Then, between August 2 and August 11 1972, the Sun experienced one of the largest solar events of space time.
NASA / Charles M. Duke Jr
This massive release of charged particles from the Sun occurred between Apollo 16 (April 1972) and Apollo 17 (December 1972) to the Moon.
This event was much greater than that of November 2025 – by a factor of 40. If it had happened while scientists were in space, the level of radiation would have caused serious illness or even death.
The Apollo crew had a lucky escape. But a solar particle event affected the Earth. The ensuing geomagnetic storm is thought to have caused 4,000 mines laid by the US to explode suddenly in Hanoi harbor during the Vietnam war, causing confusion and alarm on both sides.
NASA
There are ways to prepare for similar events in the future. The most dangerous aspect of this radiation is its high energy component, which can penetrate the protection of aircraft. The Surrey Space Center Space Environment & Protection team is currently working on a detector, called the High Energy Proton instrument, which measures this high-energy part of the sun’s radiation.
It does this by light rays produced when particles pass through a transparent medium at speeds greater than the speed of light. Astronomers often report seeing such flashes of light, even with their eyes closed, which may be caused by solar particles or cosmic rays passing through the retina or optic nerve.
Read more: Why did it take so long to get back to the Moon?
Early warning
The University of Surrey’s radiation detectors could now fly into orbit around the moon by the end of the decade. In this project, they will show danger to the bases of the moon and the Earth. NASA plans to spend US$20 billion (£15 billion) on a base on the south side of the Moon. An independent zone is proposed by China and Russia.
Radiation warning systems can give scientists the time they need to return to storm shelters inside the facility or spacecraft where additional and specially designed shielding is used.
NASA
If the astronauts aboard Orion – the spacecraft used on Artemis II – receive a warning of a solar storm in advance, they are instructed to go into storage pods on the flight deck. This puts the crew close to the Orion’s heat shield, making this area one of the most protected parts of the vehicle.
Warning systems can also help Earth. During periods of high solar radiation, controllers could order planes to fly at low altitudes and high altitudes – and in extreme cases stay on the ground.
Computer revolution
One major difference between the Apollo and Artemis missions is the rapid development of microelectronics since the 1960s and 70s. This has led to a trillion-fold increase in computer memory and a thousand-fold improvement in speed.
Apollo computers were pioneers, but they struggled to cope with the heavy workload when Neil Armstrong and Edwin “Buzz” Aldrin landed on the moon during the Apollo 11 mission in 1969. However, there is a problem with this since the technology installed in the latest flight is vulnerable to radiation.
Read more: Heat shield safety concerns raise stakes for Nasa’s Artemis II Moon mission
Charges from individual components often exceed the amount required to change the state of the computer’s memory components. In some cases it can damage the device. It is now being debated whether the biggest risk of solar flares is to the health of astronauts or to the flight electronics in space.
In 1972, the Apollo astronauts were very lucky. In this new age of exploration, when many countries have plans to visit deep space, we cannot afford to leave the safety of astronauts to chance.
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