for each wavelength channel, but otherwise identical. The photcathodes - FUV (CsI), NUV (CsTe), and VIS (S20) - are on the inside of 40mm MgF$_2$2 windows, releasing electrons to be accelerated across a small gap to a microchannel plate stack. The resulting electron cloud illuminates a phosphor, whose light passes through a fibreglass taper, to be read out by a CMOS chip with 512 pixels on a side. Photon events are centroided to 1/8 pixel to accumulate the final science images. The systems can also be run in ‘integrate’ mode when photon fluxes are too high - principally in the optical channel - which lowers the spatial resolution, but allows centroding to sufficient precision to track and compensate for spacecraft drift, in accumulating the final UV images. There are three different centroiding algorithms to choose from, and a bright-object shutdown. The full field is read at 29 Hz, but subarrays can be read up to 600 Hz for bright targets or for finer time resolution.

These detectors differ from those flown on FUSE and GALEX in having a readout array of pixels, rather than delay lines (e.g. Morrissey et al 2009, 2011, Sahnow et al 2000). They also differ from 