Ensuring continuous radiation monitoring in space with fiber-based dosimetry

• ESA astronaut Thomas Pesquet on board the ISS, testing the LUMINA fiber-based dosimeter developed by Exail/LabHC/CNES/CERN | Credits: ESA/NASA–T. Pesquet

Since its deployment on board the International Space Station (ISS) in 2021, the LUMINA fiber-based dosimeter developed by Exail and Hubert Curien lab, supported by the French Space Agency (CNES) and calibrated at CERN, has been successfully collecting data, thanks to ESA astronaut Thomas Pesquet and Emirati astronaut Sultan Al Neyadi, providing valuable insights.

CNES is now further investing in this pioneer technology. Several future deployments are already scheduled, starting with GlowRIA, a miniaturized fiber-based dosimeter to be launched on board a CubeSat in the coming years.

LUMINA: demonstrating the potential of fiber-based dosimetry for the monitoring of astronauts’ radiation exposure

The LUMINA demonstrator is an active dosimeter based on specifically designed radiosensitive fibers, capable of collecting data for several years, which is regularly transmitted back to Earth for analysis. Data from 699 days of dosimetry on-board the ISS, analyzed and published in February 2024¹, demonstrates LUMINA’s sensitivity to low and continuous radiation level, typical of the ISS orbit around Earth.

Data from 2 days of dosimetry on-board the ISS (M. Roche and al., IEEE TNS, 2024)

The sensor has shown the capability to accurately detect localized events such as the crossing of the South Atlantic Anomaly (SAA) above Brazil, where Earth’s magnetic field is weaker, leading to higher radiation levels. Additionally, LUMINA captured responses to moderate solar storms that have occurred in the last years. In Spring 2024, a much stronger solar storm occurred, and data from this event are currently being analyzed at the Hubert Curien lab.

One of the primary advantages of the fiber-based technology, beyond being unaffected by temperature and more sensitive to low radiation doses, is its equal sensitivity to all types of radiation (electrons, protons, gamma rays, X-rays or neutrons) whereas current dosimeters are designed to measure a specific type of radiation. This is particularly important in the complex space environment, which is filled with a wide range of particles.

LUMINA is a breakthrough experiment, demonstrating the potential of fiber-based dosimetry in space. The technology shows great promise as an active sensor for monitoring astronaut exposure to radiation on the ISS. It could play a crucial role in future long-distance missions to Mars by alerting astronauts to solar storms before they occur.

“A solar flare begins with a precursory wave, primarily composed of photons generating X-rays, which are not harmful but that can be detected by LUMINA. Minutes or hours later, a second, more powerful and dangerous wave follows. The delay between these two waves provides astronauts with enough time for to reach protected areas of the ISS, and to potentially shut down critical electronic systems.” Martin Roche, PhD Student at CNES/Hubert Curien lab (LabHC).

From a strong expertise in radiation-sensing fiber manufacturing to fully integrated dosimeter

The fiber-optic active dosimeter developed for LUMINA features an optical architecture manufactured by Exail, integrating two fiber-optic coils that span several kilometers. Exail collaborated closely with Hubert Curien Lab² to design the radiosensitive single-mode fibers, specifically tailored to meet mission requirements at Exail’s Lannion site.

For over two decades, Exail has been manufacturing specialty optical fibers operating at 1550 nm, for use in its fiber-optic gyroscopes in satellite inertial navigation systems. These optical fibers darken when exposed to radiation. This phenomenon previously viewed as detrimental, was turned into an advantage by leveraging the complex darkening effect to monitor radiation exposure. As radiation creates defects in the fiber, it causes optical losses by reducing the light signal output. By correlating this optical loss to radiation exposure, even at very low levels, the technology enables real-time exploitation of the “Radiation Induced Attenuation” (RIA) to monitor the Total Ionizing Dose (TID). The radiosensitive fiber developed by Exail was designed to provide a radiation monitoring that is independent from both the radiation dose rate, the particle type and energy, as well as the temperature.

“We needed to strike the perfect balance when selecting the fiber length, between the injected optical power and the wavelength of each channel, taking into account the expected optical losses during the mission and the sensibility required for monitoring radiation levels. In the end, it seems that we made a right choice for LUMINA.” Martin Roche, PhD Student at CNES/LabHC

Exail not only manufactured the fibers coils but also integrated them into the dosimeter’s architecture. CNES and ESA handled the final integration steps on the ISS and managed the overall project. Meanwhile, CERN contributed by performing calibration tests on the LUMINA dosimeter under specific radiation sources that enable the continuous exposure to very low radiation doses³.

The LUMINA dosimeter counts a 7-km channel in the Infrared domain (1550 nm) and a second 2-km channel in the visible domain (at 630 nm). The two channels are complementary in terms of sensitivity. Credit: CNES/DE PRADA Thierry, 2021

GlowRIA project: a miniaturized fiber-based dosimeter for CubeSats and satellites

Building on the success of LUMINA, CNES has invested in the GlowRIA project, aimed at developing and testing a dosimeter of much smaller footprint for New Space applications. CNES’s goal with these miniaturized dosimeters is to equip satellites in various orbits around Earth, starting with CubeSats deployed in Low Earth Orbit (~400-1500 km), to monitor radiation levels at different altitudes.

“The LUMINA experiment has proven effective in detecting continuous low radiation levels inside ISS, but we also need to be able to assess the environment in more challenging environment such as Cubesat or conventional Missions outside of the ISS shielding. Assessing radiation levels and its impact on electronics is crucial, as it remains the biggest challenge when qualifying new components for space deployment. That’s why, at CNES, we are committed to advancing fiber-optic active dosimetry even further.” Nourdine Kerboub, Radiation Engineer at CNES

CNES views fiber-based dosimetry as a breakthrough technology for space application, with no competition in Europe or globally. For GlowRIA, Exail and LabHC have delivered a fiber-based dosimeter architecture that integrates a 40 mm diameter coil of radiosensitive fiber. They will leverage Exail’s know-how in the manufacturing of coils for New Space fiber-optic gyroscopes

“With GlowRIA, we can confidently say that fiber-based dosimetry is becoming a mature technology. It features smaller-diameter fiber-coils that are easier and faster for Exail to manufacture.” Nourdine Kerboub, Radiation Engineer at CNES

In development since 2021, the GlowRIA dosimeter is being integrated in 2024, for a deployment in orbit expected in 2025 or early 2026.

The GlowRIA fiber-based dosimeter, based on a 40 mm diameter fiber coil, integrated at the top of the CubeSat

Towards more advanced fiber-based dosimetry exploiting the Distributed Sensing technique

The LUMINA project has given very insightful results, and among them is the possibility to actively monitor low levels of radiation in the ISS. Therefore, the next technological step envisioned by CNES engineers is to design a distributed sensing system based on optical fibers, which would allow to do a mapping of the radiation level along the fiber.

“This technological advancement is currently being explored by our team CNES/Exail/LabHC. It will enable us to take a step further in developing a more advanced and efficient experiment. It opens up possibilities for various applications, using only one fiber, we will get multiple measurement points”. Julien Mekki, Head of the Environment and New Devices section at CNES.

For the first time, the distributed sensing technique (DTS/DAS) would be applied to radiation monitoring in the space environment. This would be a total breakthrough and Exail/LabHC are the partners of CNES to develop a flying proof-of-concept.



¹ M. Roche and al., IEEE TNS, 2024

² These developments on radiation sensing fibers were supported by a long-standing research collaboration between Exail and Hubert Curien Laboratory (St-Etienne Univ./IOGS/CNRS), through the LabH6 joint laboratory, a continuing powerhouse of innovation in the field of optical fibers for harsh environments.

³ D. Di Francesca and al. Applied Optics, 2023