The last six months of active life have been spent carrying out a number of special observational programmes to ensure that the Final Archive will not have omitted any vital astronomical observations. Notes IUE follows an elliptical orbit rangingin height between 42,000 and 26,000 km. This geosynchronous orbit keeps the satellite over the same spot on the Earth's surface so that it can be monitored continuously from Maryland and for about 12 hours per day from Spain. Apart from constraints caused by the Earth, Sun and Moon, IUE can view the entire sky. The satellite is 4.2 m long and weighs 671 kg.
Power is provided by two solar panels.
These have provided astronomers with unprecedented wavelength coverage in the ultraviolet region of the spectrum. Ultraviolet radiation cannot be studied by ground-based observatories since it is absorbed by Earth's atmosphere. IUE studied 'invisible' radiation just beyond the violet end of the visible spectrum. Many of the fundamental atomic processes taking place in comets, planetary atmospheres, stars and galaxies give rise to the emission of radiation at UV wavelengths.