New AMS Coolant System Arrived at the ISS

ISS Copyright: NASA

On November 4, 2019, at 10:10am German time, astronauts grappled the Cygnus 12 supply ship with the International Space Station’s robotic arm. Almost four tons of equipment for the ISS were on board. Among them, the coolant system for the alpha magnetic spectrometer (AMS-02) built at RWTH Aachen University.


The particle detector AMS-02 was brought to the International Space Station in May 2011 with the last flight of the space shuttle Endeavour. Since then, the seven-ton spectrometer has been measuring cosmic ray particles with unprecedented precision and has already recorded 140 billion of them. These data provide new insight into the high-energy processes of the Milky Way and allow us to investigate questions about the nature of dark matter and the matter-antimatter asymmetry in the universe. More than 500 scientists from 16 countries worked on developing the 1.5 billion dollar experiment over more than 15 years.

The central element of AMS-02 is a silicon tracker that measures the trajectories of cosmic ray particles and is operated by a closed cooling circuit at a constant zero degree Celsius. The heat produced must be dissipated into space with a coolant system.

Three of the four redundant pumps in the coolant system, initially designed for three years of operation, have now failed after eight years.

In the past four years, an international group of scientists working under the direction of Professor Stefan Schael at the RWTH Aachen University I. Institute of Physics has developed and built a new coolant system for AMS-02 that weighs about 200 kilograms and is the size of a typical refrigerator. Engineers from NASA and scientists from the Massachusetts Institute of Technology were significantly involved. The new coolant system is designed to ensure continued operation of AMS-02 until 2030.

After the arrival of the coolant system on the ISS, the most complicated part of the mission will follow in the next six weeks. Astronauts Luca Parmitano of ESA and Andrew Morgan of NASA will connect the new coolant system to AMS-02. For this purpose, four to five field missions in space with a duration of around seven hours each are planned. Eight connecting cables, only a few millimeters thick, must be exposed and cut in the AMS detector without damaging other sensitive components in the immediate vicinity.

In May 2019, the astronauts visited the AixCAVE of the university's IT Center to prepare for this mission in a virtual simulation. They were accompanied by astronauts C. Cassidy and J. Hansen, who will guide them in their work aboard the ISS.

AMS-02 is scheduled to resume operations aboard the ISS on December 11. The follow-up project AMS-100 is already being developed at RWTH. From 2030 onwards, it will continue the precision measurements of AMS-02 while offering a 1000 times higher sensitivity.