The Alpha Magnetic Spectrometer (AMS-02), a particle physics detector installed on the International Space Station (ISS), is being prepared for a major upgrade that will allow physicists to dig deeper into the mysterious behaviour of high-energy cosmic rays. Key components for the upgraded detector have been undergoing tests at CERN for more than a year and have now reached a significant milestone, by passing a complex series of development, assembly and qualification stages.
Designed to look for dark matter, antimatter and clues about the origins of the Universe, AMS-02 was assembled at CERN and has been operating aboard the ISS since May 2011. It has recorded over 250 billion cosmic rays, revealing unexpected features in measurements of positrons, antiprotons and other particles which challenge conventional astrophysical models. The addition of a new layer on top of the existing nine layers of the AMS-02 tracking detector will increase its cosmic-ray acceptance by approximately 300%. With this upgrade the AMS-02 collaboration hopes, among other things, to be able to determine whether pulsars are the source of an observed excess in the number of positrons reaching the detector, or whether the excess is due to something more exotic, such as the decay of potential dark-matter particles.
Over the past several months, CERN has played a central role in the design, integration and qualification of the new “Layer-0”. It consists of a 3-m-diameter silicon layer in a custom-built carbon sandwich engineered at CERN specifically for the challenges of space. A full-scale qualification model, equipped with a sensor that had been pre-integrated in China and Italy, was assembled in CERN’s dedicated cleanroom and finalised to fully qualify the design for launch and orbital loads. Following assembly, CERN teams conducted metrology, vibroacoustic and random-vibration tests, in collaboration with INFN laboratories in Italy, to validate the detector’s structural integrity and behaviour under simulated launch conditions.
Layer-0 will be delivered to the ISS together with a radiator extension as a single payload inside the SpaceX Dragon rocket. The new radiator extension, developed in Taiwan with supervision from CERN and NASA, uses ammonia heat pipes to dissipate heat away from the detector’s electronics and is designed to compensate for the aging of the current radiator system after 14 years in orbit. Special brackets, designed to be operated by astronauts, have been developed to allow the disconnection of the radiator extension from Layer-0 in space followed by its attachment to an existing AMS radiator during an astronaut-guided extravehicular activity.
Final integration of the flight model will take place at CERN later this year, involving 768 silicon-strip sensors assembled in China and Italy, along with precision electronics contributed by partners in Taiwan. The integration will be followed by a new testing campaign, preceded and followed by detailed metrology at CERN to ensure precise knowledge of the position of all 768 sensors.
The final test will involve calibration using a particle beam from CERN’s Proton Synchrotron, in which a robotic arm will enable precision scanning of the detector plane to map sensor responses and locations. The hardware will then be shipped from CERN to NASA’s Kennedy Space Center for launch, expected in spring 2026.
By combining international collaboration with CERN-based engineering and systems integration, the AMS upgrade exemplifies how ground-based innovation enables long-term scientific discovery in orbit.