In May 2024, the Japanese news was full of stories about unusual displays of colorful auroras—rare sightings at low latitudes, the result of high-energy space radiation from a major geomagnetic storm triggered by an immensely powerful solar flare. On Earth, space radiation can entertain us with beautiful dancing auroras, but in space it can have serious impacts on satellites, spacecraft and astronauts. Understanding and overcoming the effects of this radiation is necessary if we are to safely advance space exploration—but even getting accurate measurements is something that has evaded our best efforts for decades.

The Japan Aerospace Exploration Agency (JAXA), the national agency responsible for aerospace research and for developing and launching satellites, teamed up with Toshiba, which has a long history in measuring radiation on the ground, to take on this difficult challenge.

Getting accurate measurements to counter the threat of space radiation

“Space radiation is a serious concern,” explains Dr. Yugo Kimoto, a Chief Researcher at JAXA. “It can cause the electronics of rockets and satellites to malfunction, and exposure to it can damage astronauts’ health. If we are going to realize safe space exploration, we need to be able to accurately measure radiation levels and evaluate their effects.”

However, measuring space radiation is no easy task. The term itself casts a wide net, covering X-rays, gamma rays and other electromagnetic waves, along with various particle rays, such as protons, neutrons, electrons, alpha rays, and heavy particles. Its intensity increases with altitude, as the atmosphere thins, but it also ebbs and flows and can vary greatly with time and location. Getting accurate measurements requires advanced technology.

JAXA has been long worked to improve its space radiation measuring technology, seeking to evaluate and clarify the relationship between the space environment and the degradation, malfunctions, and failures caused by the radiation on satellite components and materials. It has been analyzing observation data since 1987, when it installed radiation measuring equipment on Engineering Test Satellite V “KIKU-5” (ETS-V), and over the years, JAXA has secured significant improvements in measuring techniques. However, scientists worldwide working in this field have long been plagued by a major problem.

“There’s a phenomenon called pile-up,” says Matsumoto Haruhisa, a JAXA researcher, “And it sometimes makes it impossible to get accurate radiation measurements.”

Here’s the problem. When multiple radiation beams hit the radiation detector almost simultaneously, the signals overlap which makes it impossible to obtain accurate measurement of the number of beams and the energy levels. They literally pile up. We can see similar phenomena in other areas: when ocean waves travelling from different directions collide, they form cross waves that are high enough to capsize ships; and in auditory masking, where loud sounds hide fainter ones.

Pile-up has long stood as an obstacle to engineers in measuring radiation. Over the decades, they have developed a number of techniques to correct for its effects, and two methods are now in the mainstream: the first one is statistical correction, which estimates the probability of a pile-up occurring and corrects the measurement results, but its accuracy decreases as the frequency of pile-ups increase. The second one is pile-up removal, which determines which part of the measured value is causing the pile-up and removes it, to extract an accurate measurement.

However, as Matsumoto points out, this method comes with its own problems. “We can now determine which parts of the measured data have pile-ups, which is good. But as we improve the performance of measuring equipment, increasing its detection efficiency, energy range, and so on, the number of places where we detect pile-ups also goes up. If we remove the pile-up parts, we are left with almost no valid data.”

Moving forward through cooperation with the private sector

In its search for better solutions, JAXA started to consider technical cooperation with the private sector. It was at that point when a former Toshiba employee now working at JAXA said that Toshiba had radiation measurement technology that might provide a solution. That pointed the way to start the joint research.

From its extensive work in nuclear power generation, Toshiba has built up deep expertise in radiation measuring technology over the years. However, this knowhow was not immediately transferable in outer space.

Yazawa Hiroyuki, who has worked on radiation monitors for research institutes and nuclear fuel reprocessing projects at Toshiba Energy Systems & Solutions, recalls the first steps in the collaboration. “At nuclear power plants, you are required to measure different kinds of radiation over a wide range of intensities. We thought that we could bring this experience to measuring space radiation, but we soon found out just how difficult it was to correct for pile-up and measure correct values. It was not simply a matter of applying our existing technology and solving the problem.”

One immediate problem was the vastly different environments on earth and in space.

“Take power as an example,” says Yazawa as he explains some of the technical challenges unique to outer space. “On the ground, we have all the power we need for the measuring equipment, but its availability is really restricted in space, and the measuring equipment has to operate in severe conditions.”

The breakthrough in signal restoration

Through repeated trial and error, Toshiba’s engineers came up with a new approach: rather than trying to eliminate the pile-up, they instead restored the original signals from among the overlapping signals. This change of thinking was the breakthrough needed to overcome the problem.

“The key to signal restoration was the timing of the signal,” explains Daijiro Ito, who has developed radiation measurement devices for use in nuclear power plants and related facilities for more than 10 years at Toshiba Energy Systems & Solutions. “We made full use of Toshiba’s digital signal processing technology to get highly precise measurements of when signals occurred and developed a technology to separate overlapping individual signals and retrieve the originals.”

It works by combining two types of sensors and using advanced signal processing technology to analyze the data and separate the pile-up of overlapping signals.

As Ito explains, the iterative method, advanced mathematical processing for finding approximate solutions for linear equation systems, is at the heart of retrieving the piled-up signals. The first step is to prepare templates of average waveforms for different radiation signals. When a pile-up occurs, the templates and the precise time intervals between signals are used to gauge how much each signal is impacted by other signals. This estimate is used to formulate the observed signal as a linear combination of multiple signals, and solving this system of simultaneous equations retrieves individual signals as they were prior to the pile-up.

Five Years of Overcoming Challenges Produces Results

JAXA and Toshiba Energy Systems have collaborated for over five years now. In that time, they have faced many difficulties, but by pooling their knowhow and working together their engineers have overcome every challenge along the way. The result is a technology innovation with a significant role to play in advancing space development: it brings dramatic improvements to the accurate measurement of space radiation and will help to lower the weight and extend the life of spacecraft. The two organizations have filed a joint patent for their achievement.

The research project is at the final stage of performance verification, and if the results are favorable the next step is installation in a satellite. As Kimoto explains, the ultimate goal is to build a space radiation measuring instrument with the new technology, “and launch it into space.” Both Ito and Yazawa happily look forward to boasting to their family and friends when the rocket is launched.

The day when this technology is further refined and used to support humanity’s challenge in space is drawing closer. When it comes, it will also be a great source of inspiration for the young engineers who will lead the way in future space exploration.

* Note: Departments and titles are as at the time of interviews.