An artist's impression of EUVE on orbit. Photo: University of California at Berkeley

The mission of the Extreme Ultraviolet Explorer (EUVE) satellite has run its course, NASA said Friday. The final shutdown sequence will be conducted next month.

During its eight years in orbit, EUVE studied extreme ultraviolet (EUV) light, which is invisible to the naked human eye on the light spectrum. Its mission made several notable discoveries during the past eight years.

"We opened a new window on the cosmos with EUVE," said Dr. Alan Bunner, Science Director for the Structure and Evolution of the Universe program at NASA Headquarters in Washington, DC. "No one had thoroughly explored the heavens in the extreme ultraviolet before, and EUVE filled significant gaps in our understanding."

For example, the spacecraft's instruments showed that the interstellar medium -- the thin gas between stars -- was quite different than what most scientists and astronomers expected. The interstellar medium is now thought to contain regions of ionized gases, where electrons are taken away from the atoms. By a trick of science, this discovery means that sources of EUV light farther away than anyone ever predicted can now be seen using the right instruments.

EUVE observed EUV light from more than 1,000 sources during its nearly decade-long mission of exploration.

"EUVE opened up one of the last frontiers of astronomy, closing the crucial gulf between the two probed regions of electromagnetic radiation, Gamma-ray and X-ray at the high energy end and far- ultraviolet to visible light, infrared and radio at lower frequencies, thus making our view of the cosmos more complete," said Dr. Yoji Kondo, Project Scientist for EUVE at Goddard Space Flight Center in Greenbelt, Maryland, where the bulk of the work on the mission was conducted during the early years of the mission. Most operations later moved to the University of California at Berkeley.

EUVE was launched in July of 1992 atop a Delta 2 rocket from Cape Canaveral Air Force Station. The probe was planned to have conducted observations in space for only three years, but after repeated successes, NASA extended the EUVE mission two times.

EUVE's lack of an on-board propulsion system capable of boosting its orbit or targeting its eventual re-entry means the craft will simply fall back to Earth in an un-controlled manner in late 2001 or early 2002.

Atmospheric drag on the 3.5-ton craft will bring the EUVE down where most of it will burn up during the intense heating that occurs during re-entry. NASA says that only very small amounts of material from the satellite will survive the fiery return to Earth, and odds are those pieces will likely fall into uninhabited regions of the ocean.

NASA is not currently planning any missions to study EUV light and its distant sources, however, NASA officials say that the Chandra X-ray Observatory can take some of EUVE's workload during its remaining lifetime. Chandra is orbiting in a highly elliptical orbit around Earth that takes it a third of the way to the Moon during each revolution.