A NASA ultraviolet astronomy satellite. FUSE, a MIDEX (medium-class Explorer) mission, carries four 0.35-m far ultraviolet (UV) telescopes each with an ultraviolet high resolution spectrograph. The detectors cover the far ultraviolet band from the hydrogen ionization edge at 91 to 119 nm (nanometers), just short of the Lyman alpha line at 122 nm. These far UV spectra are used to measure the abundance of deuterium in the universe, as well as study helium absorption in the intergalactic medium, hot gas in the galactic halo, and cold gas in molecular clouds from molecular hydrogen lines.
