Cluster mission: why do we still need to calibrate instruments after 25 years?

The Cluster mission holds a unique place in space science history: it was the first-ever fleet of four spacecraft flying together in the Earth’s magnetosphere. But its legacy goes far beyond that, it set a new benchmark for data calibration, a cornerstone of its scientific success.

Launched in 2000, each spacecraft carried 11 identical instruments. Remarkably, most of these instruments were still operating until the end of operations, late September 2024. Some showed almost no degradation after nearly 25 years in space, while others naturally experienced reduced sensitivity over time.

To achieve the highest possible data quality, Cluster PI teams employed advanced calibration methods, intertwined instrument calibration procedures, and even machine learning techniques. In this presentation, we will showcase a selection of examples drawn from the latest technical reports on these calibration efforts, gathered in a special issue of JGR Space Physics, to be published in 2026.