Tiny shifts in mirrors delay use of satellite

Hopkins scientists, NASA seek solution for FUSE telescope

October 30, 1999|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

The mirrors on NASA's $108 million FUSE telescope won't stay put, and that is delaying astronomers' plans to study chemical clues to the origin, evolution and fate of the universe.

Two of the four mirrors aboard the Hopkins-built Far Ultraviolet Spectroscopic Explorer satellite keep drifting out of alignment, apparently in response to temperature changes, mission leaders say.

It's only a tiny movement; the starlight reflected by the mirror drifts by barely the width of a human hair.

But it is forcing ground controllers to stop and re-align the mirrors for each new observation, and it has postponed work on a final focusing of the telescope.

Astronomers have been confined to looking mostly at faint objects outside our galaxy, delaying some of FUSE's most important observations.

"We are concerned, but not terrified," said Hopkins physics professor Warren Moos, principal investigator on the project. "We see potential solutions."

Moos was quick to wave off any comparison between FUSE's mirror troubles and those of the Hubble Space Telescope.

Hubble was launched in 1990 with an embarrassing and costly manufacturing flaw in its mirror. Hubble's view was blurry until corrective hardware was installed in 1993.

"We're talking about alignment," Moos said of FUSE. "We have seen no evidence of a focus problem. We haven't attempted to focus it yet."

The mirror troubles are the latest in a series of problems that have kept the FUSE team at Hopkins working overtime since the satellite's launch in June.

Most have been resolved, but the three-year mission is now two months behind schedule.

"I underestimated how long it was going to take to get this job done," said Moos.

He compared the orbital checkout process to sausage-making: "Those who love space science instruments should never watch during checkout."

FUSE scientists plan to measure the density of intergalactic gases, seeking clues to whether the universe holds enough matter and mass to eventually brake or reverse its expansion.

They also hope to trace the circulatory systems that disperse new elements throughout the galaxy -- elements such as carbon, iron and silicon that are forged in stellar explosions, and from which planets and life have evolved.

And despite its problems, FUSE's preliminary findings are being described by its science team as "tremendously exciting."

FUSE is already far more powerful and sensitive than earlier ultraviolet observatories, Moos said, and early observations have yielded more than 25 scientific papers. They will be presented at the American Astronomical Society's January meeting in Atlanta.

Blair D. Savage, an astronomer at the University of Wisconsin-Madison, said, "FUSE has already produced more high-resolution spectra in the ultraviolet of extra-galactic sources than Hubble Space Telescope has done over its entire life."

University of Colorado astrophysicist J. Michael Shull, also a FUSE team member, agreed that FUSE is doing publishable science.

"But these are not the projects that require the highest resolution," he said. "I would be very disappointed in six months if we didn't have considerably better resolution than we have now."

FUSE needs all its mirrors aligned and focused to nail its No. 1 objective -- measuring the amount of deuterium in the universe.

Deuterium is a form of hydrogen created in the early universe. Scientists believe that if they can measure the relative amounts of deuterium, hydrogen and helium out there, they can infer the conditions present in the early universe, and find clues to its ultimate fate.

Savage, a member of the FUSE science team, said its start-up problems are not unique, and they might be a consequence of NASA's "better, faster, cheaper" approach to space science.

"There's less time available to fully test these devices on the ground before they're launched," he said. "So in almost every situation in-orbit checkout is going to take longer."

"At least we have a spacecraft that works," said Shull, an allusion to NASA's $125 million Mars Climate Orbiter -- another "better, faster, cheaper" mission that crashed on Mars last month because someone failed to convert guidance commands from English to metric measure.

Downsized and academic

FUSE was downsized from an earlier, $300 million plan and completed in just three years. It is the first NASA mission if its kind to be designed, built and operated by a university academic department. The FUSE control room is in the Bloomburg Center for Physics and Astronomy on Hopkins' Homewood campus.

FUSE does not take pictures. It is a spectroscopic observatory, designed to split the ultraviolet portion of starlight into its constituent wavelengths, or "spectra."

Analyses of the spectra can reveal the chemical and physical conditions in stars or galaxies, or in the dust and gas between them.

But getting started "has been a struggle," Moos said.

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