The International Ultraviolet Explorer spectrally examined the ultraviolet emissions from various objects and phenomena in the solar system and beyond. Terminated in 1996, it was heralded as the longest-running astrophysics project of the twentieth century.
The International Ultraviolet Explorer (IUE) was first conceived in Britain during the 1960’s by a group of scientists who suggested the project as a joint undertaking of the National Aeronautics and Space Administration (NASA) of the United States and the Science Research Council (SRC) of the United Kingdom. Significantly, astronomers hoped to improve their remote sensing capabilities of space by orbiting a spacecraft that spectrally measured emissions of ultraviolet light from objects within the solar system and beyond without the interference of Earth’s atmosphere. Financially and technically, the project was comprehensively supported by NASA, SRC, and the European Space Agency
Unlike visible wavelengths, ultraviolet wavelengths are emitted by Earth’s ozone layer and humid atmosphere, producing an ultraviolet planetary dayglow that has been observed and studied by other imaging platforms placed into orbit. On January 26, 1978, the IUE was launched from Cape Canaveral, Florida, aboard a Delta rocket, and was placed in an eccentric geosynchronous orbit varying from 26,000 to 42,000 miles (about 41,800 to 67,600 kilometers) above the planet’s surface to eliminate the atmospheric ultraviolet dayglow interference of the Earth during telescopic and spectrographic investigations.
Relatedly, the Dynamics Explorer satellites were launched in 1981 from Vandenberg Air Force Base in California with cameras focused on Earth rather than outward. Lower in orbit than the IUE observatory, these ultraviolet imaging platforms studied the planet’s plasmasphere and auroras during the same interim of the 1980’s and early 1990’s. Serendipitously, the Dynamics Explorer observatories discovered that Earth was continuously receiving a steady stream of small comets from beyond the orbit of Neptune, approximately ten million house-sized icy objects per year that disintegrated and sublimated in Earth’s atmosphere, undiscernibly adding more water to the planet’s ocean.
Technicians work on the lower portion of the International Ultraviolet Explorer.
The IUE was shaped somewhat like a child’s rattle with wings. It was approximately 13.8 feet (4.2 meters) in length and weighed 1,420 pounds (644 kilograms), with individual components supplied by the participating agencies and their contractors. Structurally, the IUE included extended solar panels, computers, batteries, and telemetric communications units for ground-based tracking and receiving divided between NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and ESA’s Villafranca del Castillo tracking facility near Madrid, Spain. Most important, the satellite housed a 17.7-inch (45-centimeter) reflecting telescope
Most significant, the observatory was designed to allow astronomers to operate its telescope and cameras in real time, collecting images and data as they would from ground-based observatories. With modifications, the original decommissioned receiving console for the IUE was relocated from the Goddard Space Flight Center to the Smithsonian Institution’s National Air and Space Museum for public viewing during the 1980’s. Originally, the experimental display consoles were designed and constructed by the Bendix Aerospace Systems Division through separate contracts with NASA and ESA.
Many space exploration programs, such as lunar and interplanetary missions, have specific purposes and goals administered and managed by a designated group of participants financially supported by larger space agencies. Like the Chandra X-Ray Observatory, the International Ultraviolet Explorer was a general-purpose mission. Scientifically, the observatory was available to astronomers from any academic institution that submitted a request and proposal for use subsequently approved by NASA, ESA, and SRC. With permission and supportive funding, a visiting astronomer could reserve operational time and focus the observatory’s telescope on an object of interest, then receive images and spectral data at one of the two monitoring and receiving centers in the United States and Spain.
Generally, the observatory was used to visually image and spectrographically gather information on many interstellar objects and phenomena, including planets, comets, stars, interstellar gas, planetary auroras, supernovas, galaxies, and even quasars. Not surprisingly for a pioneering orbital observatory, the IUE provided many firsts for international astronomy, including the first observation of sulfur within a comet, the first quantitative estimate of water loss from a large comet, and the first detection of the existence of polar auroras within the atmosphere of Jupiter. Although all the discoveries were important to the astrophysics community, most were obscure from the public’s perspective. Farther from Earth, the IUE provided the first evidence of stellar winds like the solar wind, gases streaming from one binary star to its companion, and the elemental abundances of materials ejected from novas. Although statistically insignificant, surprisingly, no spectral investigations of novas by the IUE found elements in the same ratios as those of the Sun.
The observatory was directed to transient phenomenon, such as Supernova 1987A,
Appropriately nicknamed the “People’s Satellite,” the IUE supported the investigations of approximately one thousand astronomers who collectively produced approximately 104,000 spectra from 10,000 different imaged objects. Consequently, the observatory produced data from a broad range of projects that resulted in the peer-reviewed publications of more than three thousand research papers between 1978 and 1997.
The observatory’s performance exceeded the expectations of its designers. Coupled with its operational popularity, financial support was extended far beyond the original three-year scope planned by its supporting agencies. Faced with budgetary constraints and competition from other burgeoning programs, NASA ended its financial and technical support of the IUE program in 1994, including research grants for visiting astronomers. Subsequently, in 1995, observatory operations were entirely transferred from NASA to ESA for astronomers to access from ESA’s facility in Madrid.
During the 1980’s, the IUE was increasingly used for extragalactic spectrographic observations as interest in extragalactic phenomenon correlatively increased within the growing astrophysics community. In conjunction with the Chandra and Hubble orbital observatories, the IUE significantly expanded the public body of astrophysical knowledge regarding the behavior of galactic and extragalactic phenomena and objects. Regardless, in 1996, the IUE program was completely terminated by ESA, much to the dismay of many extragalactic astronomers who believed the observatory had just reached its optimal period of use after nearly nineteen years of continuous, productive operation.
In actuality, only operational funding, personnel, and energy were terminated for the orbiting observatory. An extraordinary testament to its designers, builders, and collaborative public funding, the International Ultraviolet Explorer still geosynchronously orbited the Earth at the beginning of the twenty-first century. Perhaps someday it may be reactivated and once again enthrall astronomers with its capabilities.
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Abt, Helmut A., and Chayan Boonyarak. “The Scientific Output of the International Ultraviolet Explorer During Its Lifetime.” Bulletin of the American Astronomical Society 35 (2003): 1446-1447. Brief quantitative analysis and statistical review of the collective international data published as a result of observations made with the IUE during its budgeted period of operation from 1978 to 1996. -
Boggess, A., R. Wilson, P. J. Barker, and L. M. Meredith. “The History of the IUE.” In Scientific Accomplishments of the IUE, edited by Y. Kondo. Dordrecht, Netherlands: Reidel, 1987. Narrative account of the planning, design, construction, and deployment of the IUE by some of its participating project engineers. -
Devorkin, David. “Blast from the Past.” Air and Space Smithsonian 3, no. 3 (1988): 76-84. Details the use of the IUE to investigate Supernova 1987A that abruptly appeared in February, 1987. -
Underhill, A. B. “The International Ultraviolet Explorer.” Sky and Telescope 121 (1973): 377-379. Details the design and construction of the IUE prior to its launch. Accompanied by photographs of the operational control panels originally located at the Goddard Space Flight Center.
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