N° 35–1996: IUE project comes to an end after 18+ years of extremely successful orbital operations

At a meeting of the Science Programme Committee (SPC) of the European Space Agency (ESA) in February, the decision was taken to terminate the orbital operations of the International Ultraviolet Explorer (IUE) satellite on September 30. Science operations will terminate shortly before that date to allow the necessary end-of-life testing of the spacecraft. Only a year ago, when NASA - the major partner in the IUE project - decided to terminate its IUE science operations, ESA had been able to extend its support to include full responsibility for the scientific operations, under the "hybrid science operations" scheme, and thus maintain this important capability for the astrophysics community. As a consequence of the budgetary restrictions placed on ESA's Science Programme, the earlier recommendation of the Space Science Advisory Committee (SSAC), to terminate the operations of IUE in coordination with NASA in September, was accepted by the SPC.

The IUE project, using a 45cm ultraviolet telescope for spectroscopic observations in the waveband 115 to 320 nm, has been carried out jointly by NASA, ESA and the British PPARC (formerly SERC). Launched in 1978, its designed lifetime was only three years.

In July, the SPC agreed to complete the IUE Final Archive by the end of 1997, allowing the project to reprocess all its spectroscopic observations (numbering over 100,000) with a newly designed reduction, significantly improving on the normal direct processing done during the operational phase of the IUE project. The resulting homogeneous data archive on the ultraviolet radiation of cosmic sources, collected over the 18+ years of the operational project, will remain an important resource for astrophysical studies for many years to come.

This has been one of the most successful astrophysics projects in space science, with more than 3,500 papers in refereed journals based on the observational results of the spectrographs. Over 500 doctoral dissertations have used its results, clearly demonstrating the importance of the IUE project, not least for the education of the next generation of astrophysicists.

During the last six months of science operations a number of special observational programmes (Lasting Value programmes) were conducted from ESA's IUE Observatory at its ESA Villafranca Satellite Tracking Station in Spain, to make sure that the material in the Final Archive will not have missed any critical observations for which the specific capabilities of the IUE project were particularly suitable.

These last observations were all made under single-gyro spacecraft control after another gyro failure in March 1996 left the IUE with only one functional gyro, out of the original six.

These programmes were associated with planetary studies (Jupiter and its Galilean satellites in coordination with the in-situ studies of the Galileo mission); critical observations of the mechanisms associated with the stellar winds in massive stars; and a major coordinated campaign in the x-ray, ultraviolet and optical wavelengths to determine the nature of the mini-quasar in the Seyfert I Galaxy NGC 7469.