For over four decades, the European Space Agency (ESA) has listed the multipactor effect among its most persistent technical threats. This phenomenon, an avalanche of electrons that builds up inside vacuum components such as antennas and waveguides, can cause irreversible damage to satellite communications systems. Now a team from Spain's CSIC research council, working with the spin-off Nanostine and supported by ESA, has developed an invisible shield that could neutralise the threat.
The conventional defence against multipactor has been to coat vulnerable parts with Alodine, a chromium-based compound that performs well but poses serious health and environmental risks. European regulators have long pushed for its phase-out, yet no substitute has matched its technical reliability. Lidia Martínez, a researcher at the Institute of Materials Science of Madrid (ICMM), explains that the industry needed a material that emits few secondary electrons, since these are what trigger the chain reaction.
Previous attempts to solve the problem focused on modifying surfaces at the micrometre scale, but none delivered the performance leap the space sector demands. The ICMM team decided to change scale entirely. Instead of micrometric structures, they engineered a rough surface at the nanometre level, with features on the order of a billionth of a metre. Using an ultra-high-vacuum technique called a gas aggregation source, they produced gold and silver nanoparticles between four and eight nanometres in size, deposited without solvents or residues.
The result is a porous, metallic, chemically clean film. In tests carried out at ESA-accredited laboratories, the coating reduces secondary electron emission by around 30% compared with Alodine. Even more striking, the cut-off energy threshold—the point at which a material starts generating more electrons than it receives—improves by up to 300% in some configurations. The researchers also subjected the coatings to six-month ageing tests and thermal treatments at 150°C, simulating the conditions a satellite experiences in direct sunlight. Although performance dips slightly over time, it remains superior to freshly applied Alodine.
From patent to orbit
The technology is already protected by a joint European patent application filed by CSIC and Nanostine with the European Patent Office in July 2025, currently under examination. Nanostine, a spin-off created by CSIC, will handle commercialisation, targeting primarily the aerospace sector. The development was funded through an Industrial PhD programme of the Community of Madrid and supported by the ESA Business Innovation Centre, coordinated in Madrid by the Madri+d Foundation.
Despite the promising results, Martínez remains cautious about the timeline. Taking a new coating from the lab to actual use in space typically requires around a decade of testing and validation. She notes that ESA has expressed satisfaction with the proposed solution, but stresses that the project still has to clear several stages before these materials can fly on board a satellite.
The breakthrough comes at a time when Europe is investing heavily in space infrastructure, including a coalition to build a European anti-ballistic missile shield that will rely on advanced satellite technology. The new coating could also find applications beyond space, in high-power radio frequency systems and particle accelerators, where multipactor is a known hazard.
For now, the Spanish team's work represents a significant step toward a safer, more sustainable approach to protecting the hardware that underpins modern communications, navigation, and Earth observation. As the European space sector grows, innovations like this one will be crucial to maintaining reliability and reducing environmental harm.
