The long-lived International Ultraviolet Explorer (IUE) spacecraft, launched on January 26, 1978, made the last of its 111,627 astrophysical observations of about 9,300 objects on September 27, 1996. It performed spectrophotometry at high (0.1-0.3 E) and low (6-7 E) resolution between 1150 and 3200 Angstroms with a dynamic range of approximately 22 astronomical magnitudes (-1.5 to ~20th magnitude)
IUE was a three-way collaborative project among NASA, the European Space Agency (ESA), and the British Science and Engineering Research Council (now named Particle Physics and Astronomy Research Council [PPARC]) and had a three-year design lifetime. IUE operated in a real-time mode similar to ground-based observatories and was the only geosynchronous (not geostationary) astronomy satellite capable of continuous observation for 24 hours daily. It was operated 24 hours/day from NASA Goddard Space Flight Center (GSFC) and from the ESA station at Villafranca, Spain.
About two thirds of the observing time was allocated through NASA's competitive Guest Observer program with the remainder allocated through ESA's equivalent program. In all more than 2,000 Guest Observers from all corners of the world, including astronomers from North and South America, Europe, China, India, Russia, Africa, and Australia, have made IUE observations. Approximately 3,500 scientific papers based on these observations have been published in peer-reviewed journals, the largest number for any satellite observatory thus far. In addition, more than 500 doctoral students have used IUE results in their dissertations, clearly demonstrating the importance of the IUE project to the education of the next generation of astrophysicists.
Left, an example of IUE data; right, and artist's conception of the IUE in orbit.
Since the inception of the IUE program, NSSDC has played a number of vital roles. Right from the beginning, NSSDC served as the primary archive site for IUE data. Aside from maintaining the definitive primary copy of the IUE science data set, NSSDC implemented the exchange of data among the IUE project's three partners by receiving copies of observations obtained by each of the two control centers and making copies for the other center and by making copies of all observations for PPARC. Approximately 5,360 tapes were created by NSSDC in satisfying this role.
NSSDC provided 24-hour electronic access to IUE data as early as 1985 and initiated its public near-line mass storage and dissemination activities with the IUE data in November 1991. By 1996 NSSDC had about 1 TB of IUE data network-accessible from the NASA Data Archive and Distribution System (NDADS) and was experiencing significantly more accesses to IUE data than to data from any other mission. Not including NSSDC's support for the final archiving effort discussed below, NSSDC supported an average of 7,000 requests for 100,000 IUE data files during each of the past several years.
As it approached its sunset years, the IUE project with the encouragement of its scientific user community decided to create a Final Archive (FA) of all IUE data by doing a final processing using the best algorithms and calibration coefficients resulting from the many years of IUE data analysis. At this writing the final archiving of all the NASA and ESA IUE data has been accomplished. Each ground station did the final processing of the data acquired during its observing time. More details on the FA effort in general are available at http://iuewww.gsfc.nasa.gov/iue/iue_homepage.html and at http://archive.stsci.edu/iue/.
NSSDC provided significant support to the FA effort. The raw data for all observations were written to a special set of optical disks and provided to the IUE project ground/processing centers for final processing. NSSDC then received back electronically from the IUE project 1.1 TB of FA data that it ingested to NDADS. In addition, NSSDC has helped the IUE project resolve a number of apparent discrepancies in the IUE Observing Log as well as archive to archive backup support for problem data tapes.
The time elapsed from the IUE project's withdrawal from NDADS of the first raw data for final processing to the final NDADS ingest of the last-arrived IUE FA data was 78 months (60 months of active [FA] data ingest, June 1993 - May 1998).
Over the last couple of years, the NASA space science data archive and dissemination environment has evolved significantly. Most notable has been the emergence of the Space Science Data Service (SSDS) discussed in previous newsletter issues. The SSDS is a fresh approach to enhancing the interoperability among the multiple sites of NASA's space science data environment.
In particular, the SSDS emphasis on having active archives of discipline expertise supporting science data preparation and usage led to the Space Telescope Science Institute (STScI), until then NASA's data management, dissemination, and archiving site for HST data, being additionally designated as the active archive for IUE data.
Under terms of an Memorandum of Understanding (MOU) signed in 1997 by STScI, the Goddard Laboratory for Astronomy and Solar Physics (which had hosted the IUE Project) and NSSDC, the primary pathway to IUE data will be through STScI interfaces, and the most frequently accessed IUE data will be made accessible from STScI mass storage systems. All IUE data will remain network-accessible to STScI interfaces on NSSDC's NDADS system for the indefinite future. Permanent archiving of IUE data will remain an NSSDC responsibility.
To support early users of the IUE FA data (produced with the "NEWSIPS" software), STScI hired onto its Computer Sciences Corporation (CSC) support staff a number of CSC people who until then had been supporting the GSFC IUE project in the development and implementation of the NEWSIPS software.