NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite will reach a major milestone on Thursday, June 24, 2004 - the five-year anniversary of its launch atop a Delta-II rocket from Cape Canaveral in Florida.

The 18-foot tall, 3,000 pound satellite continues to operate from its perch nearly 500 miles above the Earth's surface, gathering unique data about everything from planets and nearby stars to galaxies and quasars billions of light years away. Groundbreaking science done during FUSE's five years in orbit include the first-ever observation of molecular nitrogen outside our Solar System; confirmation of a hot gas halo surrounding the Milky Way galaxy; and a rare glimpse into molecular hydrogen in Mars' atmosphere, among others. By its fifth anniversary, FUSE will have collected more than 47 million seconds of science data on more than 2,200 unique objects in the cosmos.

"The sheer magnitude and amount of scientific work that is being produced using FUSE is beyond even what we had imagined," said Warren Moos, FUSE's principal investigator from The Johns Hopkins University's Krieger School of Arts and Sciences in Baltimore. "Scientists working with FUSE have produced a steady flow of papers - a half dozen a month – each representing a major scientific study. What has been accomplished is extremely impressive and very satisfying."

Designed and operated by a team of engineers and scientists at Johns Hopkins, FUSE is the largest astrophysics mission NASA has ever handed off to a university to manage. The project also has input from the Canadian and French space agencies

"Astronomers are using FUSE to produce very exciting and unexpected results," said George Sonneborn, FUSE Project Scientist at NASA's Goddard Space Flight Center, Greenbelt, Md. "FUSE has discovered a new component of the Milky Way galaxy, is charting very hot gas in the vast regions of universe between distant galaxies, and is probing the nature of disks of gas and debris around young stars where planets may form."

FUSE comprises four telescopes that function as a single instrument, dissecting far-ultraviolet light from distant objects into high-resolution spectographic information used by astronomers from around the world. With more than 10,000 times the sensitivity of its predecessor - the Copernicus satellite in the 1970s - FUSE complements the Hubble Space Telescope by observing light at wavelengths too short for that instrument to see. Since its launch, astronomers have used FUSE to study stars and nebulas in nearby galaxies, to discover a new component of the Milky Way galaxy and even to probe the vast regions of space between distant galaxies in the universe.

Despite the obvious successes, there have been times over the last five years when serious problems threatened the satellite's pointing control system and thus, the mission itself. In late 2001, when two of the device's four reaction wheels - components that point the satellite's telescopes and keep them steady - stopped working, leaving the mission in peril.

Rather than close up shop as some feared, FUSE scientists and engineers collaborated intensely for two months and devised a solution: using a combination of software and other hardware to mimic the functions of  the missing wheels.

"It's been a real roller-coaster ride," says William P. Blair, FUSE's chief of observatory operations and physics and astronomy research professor at Johns Hopkins. "But we've overcome the problems and, if anything, FUSE is now working better than ever."

For more information on NASA and FUSE, go to   http://www.nasa.gov and  http://fuse.pha.jhu.edu