After 8 years, crippled observatory refuses to go gently

Shutting down an old and crippled satellite isn’t as simple as pulling a plug.

In fact, scientists and engineers at Johns Hopkins University worked late into the day Thursday trying to drain the stubborn batteries of NASA’s orbiting FUSE observatory and putting to rest an eight-year mission that tested their ingenuity and patience to the very end.

For one astronomer, it was particularly melancholy. “It’s sad -- I’m a big loser here,” said Steve McCandliss, who has been has been working on the FUSE project since his days as a grad student in 1981.

For the news cameras, the FUSE team had planned a little mission-ending theater, turning the satellite’s solar panels away from the sun one by one and letting the control-room monitors go dark.

A group gathered in a basement hallway to toast the space telescope with champagne.

“It’s a sad thing to turn a satellite off, but we had a lot of great years,” said Warren Moos, Hopkins astronomer and physicist, who was principal investigator for FUSE.

But a few feet away, in the FUSE control center, engineers were still laboring before computer screens, battery voltages stubbornly refusing to drain.

By design, satellites like FUSE are hard to kill.

For example, to prevent solar batteries from overcharging and potentially exploding, controllers had had to trick the spacecraft’s electronic brain into accepting drained batteries as fully juiced.

At 5:27 p.m., the telescope responded to its last command. “It put up a good fight, but we finally got it turned off,” said William P. Blair, chief of FUSE operations at Hopkins. It should stay in a deep sleep until it falls back through the atmosphere in 30 years or so.

The telescope’s $225-million scientific mission actually ended July 12, when the last of the telescope’s four troublesome “reaction wheels” ground to a stop, making it impossible to aim at stars and galaxies.

It was the last in series of extraordinary technical problems that had forced controllers to devise innovative fixes, all without laying an astronaut’s glove on the telescope. FUSE flew too high for shuttle repair missions.

“We had been plagued with this in a way no other science mission ever had,” said Blair. But “you can’t complain about getting eight years out of a satellite designed for three.”

In all, FUSE -- Far Ultraviolet Spectroscopic Explorer -- made observations of 2,800 celestial objects.

Astronomers who used FUSE have published more than 1,200 scientific papers, Moos said, “and they keep on coming.” The processed data are being stored for future researchers at the Multimission Archive at the Space Telescope Science Institute in Baltimore.

As a spectroscopic telescope, FUSE broke starlight down into its constituent spectra, or wavelengths, so scientists could study the chemistry, velocity and temperature of objects and regions invisible to telescopes on the ground.

Over the years, for example, scientists confirmed the existence of a halo of hot gas around the Milky Way galaxy -- the exhalations of exploding stars.

They also looked for molecular hydrogen on Mars, a remnant of the planet’s vanished water.