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Engineers have repaired one of the Hubble Space Telescope's main cameras, after electronics problems had put it out of action.

The Advanced Camera for Surveys (ACS), which has produced some of Hubble's most dramatic images, started up again on Sunday night, 2 July, after having been shut down for nearly two weeks.

Mission operators were understandably thrilled. "Now we can get back to doing more incredible science," said Ed Ruitberg, deputy associate director for astrophysics at NASA's Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

On 19 June, the power supply to the camera shut off because the voltage was, for unknown reasons, outside acceptable limits for the instrument. Engineers fixed it by switching to a backup set of electronics on 30 June.

No crucial science observations were lost when the camera was offline, says Hubble's senior project scientist David Leckrone. But some work will be delayed: when it shut down the telescope was going to make follow-up observations on the Hubble Ultra Deep Field, a survey of distant galaxies. That work will be rescheduled for the autumn, Leckrone says.

Astronauts put the ACS on board Hubble during a 2002 mission to service the telescope. The camera is a set of three detectors that peer at the universe in different wavelengths, from the ultraviolet to the near-infrared. The problem with the power supply affected two detectors; the third was receiving power from a different source.

The Hubble's three other science instruments have continued to work properly, Ruitberg says.

Hubble trouble

"Over the life of the machine," says Ruitberg, "we've experienced problems all along the way. We've always figured out a way to solve those problems." In 2001, the Space Telescope Imaging Spectrograph instrument went offline. It was rebooted and worked for another three years before retiring.

Mission planners are expecting the ACS to last for the rest of Hubble's lifetime - however long that will be. The telescope has already worked for more than 15 years, with astronauts swapping its instruments every few years.

NASA administrator Michael Griffin has yet to decide whether to send one final servicing mission to the telescope before shutting it down and letting it drop into the ocean. That decision will depend in part on whether the shuttle programme successfully continues; the next flight is currently slated for 4 July.

The Hubble's successor, the James Webb Space Telescope, is not due to launch until at least 2013.

As well as repairing the ACS, the telescope's operators carried out a few other tweaks. They dropped the operating temperature of one of the detectors aboard the ACS from -77 °C to -81 °C, which should make it work slightly better.

"We're getting a little bonus," says Leckrone.

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