FUSE Space Telescope Reaches the End; Astronomers Say Farewell

The intrepid never-say-die space telescope known as FUSE has finally reached its mission's end and will be turned off after more than eight years of discoveries on everything from planets and nearby stars to galaxies and quasars billions of light-years away.

The satellite's control room on the Johns Hopkins Homewood campus will go dark on Oct. 18, leaving the satellite itself — its pointing system so often pulled from the brink of inoperability by enterprising engineers and scientists in that control room — to continue circling the Earth. Eventually, decades from now, its orbit will decay and the satellite will burn up in the atmosphere.

"It has been a great run. Who would have believed that a mission designed for three years would have gone on producing great science for eight," said Warren Moos, Gerhard H. Dieke Professor of Physics and Astronomy at Johns Hopkins and FUSE principal investigator. "What a testament to the ingenuity and hard work of the FUSE team."

FUSE, short for Far Ultraviolet Spectroscopic Explorer, was a Johns Hopkins-managed NASA mission that complemented the Hubble Space Telescope with observations at short ultraviolet light wavelengths below the range in which Hubble operates. Its original, three-year science mission was extended by NASA three times.

Astronomers from around the world have published more than 1,200 papers based on data from the satellite, which was launched atop a Delta-II rocket in June 1999 from Cape Canaveral. FUSE produced not pictures of distant objects but spectrographs, which are digital "charts" that break down the light emitted by those objects. By analyzing FUSE data, astronomers were able to measure temperatures, densities and chemical compositions of objects near and far, helping to place them in context in the history of the universe.

Groundbreaking science done during FUSE's eight years include a rare glimpse into molecular hydrogen in Mars' atmosphere, confirmation of a hot gas halo surrounding the Milky Way galaxy and a first-ever observation of molecular nitrogen outside our solar system, among others.

George Sonneborn, FUSE project scientist at NASA Goddard Space Flight Center in Greenbelt, Md., said, "JHU has done a fantastic job delivering a top-quality science mission for NASA."

FUSE is the largest astrophysics mission that NASA has ever handed off to a university to develop and then operate. The 18-foot-tall, 3,000-pound satellite has been run by a group of about 25 scientists, engineers and support staff from a basement-level control room in the Bloomberg Center for Physics and Astronomy.

Though FUSE's mission has been astoundingly successful from a scientific point of view, it faced a number of "death-defying" adventures dating back to late 2001. That's when, during a two-week period, two of the four "momentum wheels" that helped researchers aim the satellite at its targets stopped working. At least three wheels were needed to point FUSE with the precision needed for accurate astronomical observations.

Left with no other choices, the operations team conceived of and created a modified control system that used other devices onboard the satellite-electromagnets called magnetic torquer bars — to stabilize the satellite's pointing by periodically pushing or pulling the satellite against Earth's magnetic field. In just eight weeks, FUSE was back in business.

"It was a tenuous control at first, but it was certainly better than nothing," recounted Bill Blair, a research professor in the Henry A. Rowland Department of Physics and Astronomy and FUSE's chief of operations. "But with time, tweaks and experience, we got back into a very respectable science operations mode."

The satellite remained stable until Dec. 27, 2004, when yet another momentum wheel stopped operating, leaving the satellite with just one.

"True to form, we figured out how to use the magnetic trick to work with the single remaining wheel. But it was a lot harder than it sounds," Blair said.

It took most of 2005 to coax the satellite back into an effective operational mode, but from November 2005 into the spring of this year, FUSE was again gathering data. On May 8, however, the last momentum wheel malfunctioned. Researchers and engineers believe that some source of excess friction slowed the wheel. After studying the problem, the operations team was able to restart the wheel and put the telescope back into service.

"From June 12 to July 12, the wheel performed again almost flawlessly," Blair said. "But then the 'wheels came off,' so to speak. The wheel operated perfectly right up to the end, and then it just stopped dead, probably indicating a catastrophic failure of some kind."

After a month of creative troubleshooting, the FUSE team had to face the sad fact that the satellite's science mission was, at last, at its end.

"The magnetic system just doesn't have enough muscle by itself to point and hold the satellite for astronomical observations," Blair said. "We contacted NASA and told them the science mission was over."

Now the team has less than a year to close out the mission, including reprocessing and archiving some 131 million seconds of science data, writing final reports and providing final documentation of the mission. FUSE's scientific data will remain available to astronomers for years, however, through a data archive at the Space Telescope Science Institute, which is located on the Homewood campus.

One part of the closeout process is concluding on-orbit operations and turning off the satellite. Until now, FUSE has continued to take end-of-mission calibration data and perform engineering tests of various kinds. But Oct. 18, FUSE gets "put to sleep" for good. After 30 years or so, its orbit will decay and FUSE will burn up in the atmosphere.

"After that Thursday, FUSE will be just another piece of space junk, orbiting the earth every 100 minutes or so. It is a sad and ignominious end to such an outstandingly successful mission," Blair said. "But a tremendous scientific legacy is left behind. I commend the team of scientists and engineers who have worked so hard over the years to wring every last bit of science we could out of this amazing satellite."

Source: Johns Hopkins University

Related stories:

NASA Concludes Successful Fuse Mission
After an eight-year run that gave astronomers a completely new perspective on the universe, NASA has concluded the Far Ultraviolet Spectroscopic Explorer mission. The satellite, known as FUSE, became inoperable in July when the satellite lost its ability to point accurately and steadily at areas of interest. NASA will terminate the mission Oct. 18.
Assisting NASA in biology mission, Stanford helps E. coli visit the final frontier
Banished from kitchen counters, E. coli, albeit a harmless variety, are taking to space. On Saturday, Dec. 16, 2006, bacteria hitchhiked into low-Earth orbit aboard an Air Force Minotaur 1 rocket that took off from the NASA Wallops Flight Facility in Virginia in an experiment to test the effects of space on living organisms.
Surprising telescope observations shake up galactic formation theories
A heavy form of hydrogen created just moments after the Big Bang has been found to exist in larger quantities than expected in the Milky Way, a finding that could radically alter theories about star and galaxy formation, says a new international study led by the University of Colorado at Boulder.
Venerable ultraviolet satellite returns to operations
NASA's Far Ultraviolet Spectroscopic Explorer astronomy satellite is back in full operation, its aging onboard software control system rejuvenated and its mission extended by enterprising scientists and engineers after a near-death experience in December 2004.
Hubble Survey Finds Missing Matter, Probes Intergalactic Web
Although the universe contains billions of galaxies, only a small amount of its matter is locked up in these behemoths. Most of the universe's matter that was created during and just after the Big Bang must be found elsewhere.
Rossi X-ray Timing Explorer Satellite Pins Down Timer in Stellar Ticking Time Bomb
Using observations from NASA’s Rossi X-ray Timing Explorer (RXTE), an international team of astronomers has discovered a timing mechanism that allows them to predict exactly when a superdense star will unleash incredibly powerful explosions.
Researchers mine the 'Terahertz gap'
Research underway at the University of Leeds will provide a completely fresh insight into the workings of nano-scale systems, and enable advances in the development of nano-electronic devices for use in industry, medicine and biotechnology.
Images of Saturn's Small Moons Tell the Story of Their Origins
Imaging scientists on NASA's Cassini mission are telling a tale of how the small moons orbiting near the outer rings of Saturn came to be. The moons began as leftover shards from larger bodies that broke apart and filled out their "figures" with the debris that made the rings.

News discussion:

Space & Earth science news