The International Ultraviolet Explorer (IUE) was launched successfully
on 26 January 1978, from Cape Canaveral, Florida. The satellite was
developed to provide a general facility for observing ultraviolet (UV)
spectra of astronomical sources over the wavelength range from about
1150 A to 3200 A.  The project has been a joint undertaking in which
the US National Aeronautics and Space Administration (NASA) provided
the spacecraft, the optical and mechanical components of the scientific
instrument, the US ground observatory and spacecraft control software;
the UK Science Research Council (SRC) in collaboration with University
College London (UCL) provided the television cameras used to record the
spectroscopic data; and the European Space Agency (ESA) provided the
solar arrays and European ground observatory. The image processing
software was developed jointly by NASA and the SRC's Appleton
Laboratory. The satellite has been placed in geosynchronous orbit over
the Atlantic Ocean and is operated for 16h each day, for NASA sponsored
observers, from the US ground observatory located at the Goddard Space
Flight Center (GSFC) near Washington, D.C., and for the remaining 8h by
ESA, for ESA and UK sponsored observers, from the European ground
observatory located near Madrid.
 
A synchronous orbit has other advantages. Because the Earth subtends
an angle of only 17 degrees the unconstrained area of sky is much
greater than for low orbits and, as its movement along the ecliptic is
at the diurnal rate, the occurrence of occultations is infrequent.
Consequently, over large portions of the sky, neither long exposures
nor the observation of variable phenomena need be periodically
interrupted. A penalty is that in synchronous orbit observations are
normally made in full sunlight so the telescope must be baffled to
ensure adequate rejection of stray sunlight and earthlight.  The offset
guiding system can be influenced, however, and relatively bright guide
stars are needed near the Earth's limb.
 
The IUE mission was terminated on Sept 30, 1996 at 18:42 UT after a life
span of 18 years, 8 months, 4 days, 1 hour and 6 min.