Death in the ultraviolet.

After years of physical decline and several attempts to cut its funding, the venerable International Ultraviolet Explorer (IUE) spacecraft has finally fallen under the budget ax. On Sept. 30, the European Space Agency and NASA shut down all operations of the 18-year-old craft. Launched in 1978 and expected to last just 3 years, the IUE endured, taking ultraviolet spectra of more than 100,000 celestial targets, from comets to quasars.

Although it made ultraviolet observations until the very end, the aging craft had suffered a series of mishaps in recent years. A gyroscope failure last March left it with just one working gyro out of the original six, and engineers had to scramble to keep the craft from rotating haphazardly.

Unwanted light scattering into the IUE's fine-error sensor, a device that keeps targets in the field of view by tracking nearby guide stars, had made it more difficult to conduct observations. Solar panels, which power the craft, had degraded, and the damage wrought by 18 years of exposure to ultraviolet radiation in space had steadily heated the IUE's spectrograph, posing problems for electronic devices.

"We've been hanging by our fingernails at times," says Andrew G.

Michalitsianos, former deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. Even if funding hadn't been cut, "I think from a technical point of view, IUE would not have lasted beyond a year." Veteran ultraviolet astronomer Jeffrey Linsky of the University of Colorado at Boulder acknowledges such handicaps. Nonetheless, he says, "the craft produces very useful data despite the fact that it's 18 years old.

"The science per dollar coming out of IUE is very high. If it suffered a death from natural causes-fine. But I would call this murder. NASA should have continued the mission," he adds.

Astronomers mourn IUE's passing on several counts. The craft was placed in a geosynchronous orbit so it would always reside above the same spot on Earth.

This enabled ground controllers to monitor IUE continuously and to point it at short notice toward newly discovered celestial phenomena. In addition, the altitude of its orbit, which varied between 42,000 and 26,000 kilometers above Earth, gave the craft a nearly unobstructed view of the heavens and allowed it to examine an object for hours at a time. In contrast, the Hubble Space Telescope has a low orbit. Earth looms large and blocks observations for about half of each 90-minute pass completed by the telescope. Hubble's primary mirror has four times the diameter of the mirror on IUE, and the telescope's two ultraviolet spectrographs have higher sensitivity and spectral resolution than the single IUE spectrograph. Yet IUE's ability to conduct long-term observations made it better for extended studies, such as tracking comets and monitoring the periodic flare-ups of variable and binary stars, Michalitsianos says. Among its triumphs, IUE played a key role in monitoring the stellar explosion supernova 1987A, was the first spacecraft to detect molecular sulfur in a comet, and just last March examined the bright comet Hyakutake. "Many ultraviolet astronomers cut their teeth" on the IUE, notes project scientist Yoji Kondo of Goddard.

Astronomers are now compiling an archive of IUE spectra, which should be available late next year. Meanwhile, for the next few centuries at least, IUE will remain mute in its current orbit.