The IUE Spectral Image Processing System, known as IUESIPS, was the standard production processing system used for IUE data from the beginning of the mission. The system was used to apply standard calibrations and extractions to the raw data, and provide standard data products to IUE Guest Observers.
The IUESIPS software was used to process IUE data over a nearly 19 year time span. During that time, there were many changes to the processing algorithms and calibrations. When requested by researchers, images were reprocessed with more up-to-date software, but most of the data were never reprocessed with IUESIPS. The IUESIPS archive is thus rather heterogeneous, reflecting the many changes made to the processing system over time.
During the last several years of the IUE Project, the new, improved processing system known as NEWSIPS was developed and put into place. All IUE data have been reprocessed with the NEWSIPS software to produce the IUE Final Archive. However, many of the papers in the literature are based on the IUESIPS version of the data.