The High-Energy Light Isotope eXperiment (HELIX) is a balloon-borne particle detector designed to measure the flux of cosmic rays confined to the Milky Way Galaxy by its magnetic field. Its main goal is to determine the abundance ratio of unstable ¹⁰Be to stable ⁹Be, thereby helping scientists to probe the size and shape of our Galaxy’s magnetic field. To carry out this task requires lifting a two-tonne spectrometer, based on a superconducting magnet, to the edge of space using a giant helium-filled balloon.