New issue shuts down camera on Hubble

NASA hopes instrument will be working next week

September 29, 2006|By Frank D. Roylance | Frank D. Roylance,SUN REPORTER

The Hubble Space Telescope's workhorse camera is on the fritz for the second time since June.

Officials at the NASA Goddard Space Flight Center said yesterday that the problem with the $86 million Advanced Camera for Surveys may be as simple as a sticky mechanical relay. If it can't be fixed, they are hoping they can still have most of the camera's components working again by next week.

"We're doing testing, and we're going to see if we can revive it," said Preston M. Burch, Hubble program manager at Goddard.

A similar shutdown occurred June 19, when the power supply to the same instrument failed. Scientific observations continued using Hubble's other instruments while engineers worked on the problem.

The ACS was fully revived June 30, when controllers switched to a backup power supply. Observations resumed a few days later.

The two incidents stem from "totally different problems," Burch said. "They have nothing in common."

Hubble's latest troubles began Saturday as controllers were switching from the instrument's so-called "solar blind channel" to its "high resolution channel," or HRC.

The HRC is one of three "channels" that function as three separate cameras within the instrument, Burch said. It provides scientists with their sharpest view of the heavens, but it is used for just 10 percent of the instrument's science.

An onboard computer sensed that electricity was not reaching part of the HRC's sensor chip, so it shut the entire camera down and called for help from Goddard.

Burch said the failure is not a symptom of aging in the 16-year-old observatory. The faulty relay is a mechanical switch designed to cycle many thousands of times, he said. But it's just 4 1/2 years old now, and has cycled a mere 500 times.

"This is an unusual failure, to have a relay of this type fail so early," he said.

If the relay can't be revived, Burch said, it will mean a permanent loss of power to half of the chip that serves as the HRC's light sensor, making it blind to half its normal field of view.

Observations of individual objects won't be affected, he said. Scientists can simply aim more precisely to place the light from their target stars on the surviving portion of the chip.

For observations targeting wider portions of the sky, he added, astronomers will have to take more pictures to cover the region. And that will take more time.

While Goddard's experts were troubleshooting the problem, observations using Hubble's other instruments continued, Burch said. But the space telescope's ills draw new attention to the more serious problems scientists may face as Hubble's batteries and gyroscopes near the end of their life expectancy.

Engineers have said a breakdown capable of halting Hubble's scientific work could occur as early as next year, although controllers have made operational changes aimed at keeping batteries and gyroscopes alive until astronauts can replace them.

NASA Administrator Michael Griffin has said he may decide as early as next month whether to order a fifth and final Hubble servicing mission before the shuttles are grounded in 2010.

Earlier, he said the go-ahead would hinge on the performance of the shuttles during their past three flights. All three have landed safely.

Griffin's predecessor, Sean O'Keefe, canceled plans for future servicing flights because of safety concerns raised by the 2003 loss of the shuttle Columbia and its crew of seven.

He argued that shuttle astronauts faced with an emergency during a flight to the International Space Station could take refuge there and await rescue. But the station's orbit would be inaccessible to astronauts launched on a mission to Hubble.

frank.roylance@baltsun.com

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