Breaking through the geocoronal barrier: spectroscopic validation of the hydrogen absorption cell for Lyman-alpha attenuation

The Johns Hopkins Rocket Group is developing a hydrogen absorption cell to mitigate the Lyman-alpha emission challenge posed by the geocorona for astronomical observations in the Lyman ultraviolet (LUV) spectrum (100-120 nm) from low-Earth orbit. This prototype, a low-pressure (~3 torr) stainless steel chamber with two lithium fluoride (LiF) windows, enables transmission down to about 103 nm. It thermally dissociates molecular hydrogen into atomic form using a heated tungsten filament, absorbing Lyman-alpha radiation and preventing resonant scattering. Our preliminary results with the Long-slit Imaging Dual Order Spectrograph (LIDOS) reveal variations in Lyman-alpha absorption with different filament types and indicate potential molecular hydrogen fluorescence and electron impact excitation. These findings are vital for advancing hydrogen absorption cell technology in future LUV missions.