A joint NASA–ESA–UK ultraviolet astronomy satellite launched in 1978 January. It carried a 0.45-m telescope, with two spectrometers covering the wavelength ranges 115–200 and 190–320 nm, both at low and high resolution. From a geosynchronous orbit the satellite observed targets from Solar System objects to bright stars and extragalactic objects as faint as 21st magnitude. IUE was switched off in 1996 September after 18 years, having become the longest-lived astronomical satellite.

http://sci.esa.int/iue/31284-summary/ ESA mission website.