The Hubble Space Telescope's most frequently used instrument, the Advanced Camera for Surveys (ACS), has shut down unexpectedly. Hubble's managers are still investigating the problem, but they are optimistic that they will be able to use the camera again soon.
ACS has three channels, which are essentially three different cameras. The problem appears to be confined to the High Resolution Channel (HRC), which has the sharpest vision, but is used in only about 10% of ACS observations.
It is often used for detailed observations of planets and other objects in our solar system because its resolution is twice as good as that of the Wide Field Channel (WFC), which is the instrument's most frequently used channel. The WFC has been used to spot galaxies in the very early universe, among other observations.
Hubble's computer shut the ACS down automatically at 1521 GMT on Saturday when it detected that the power supply voltage for the HRC, which is normally at 35 volts, had dropped to zero.
It is not the first time the ACS has had problems. It briefly stopped working in June when its original power supply failed but was brought back online when managers switched to backup power (see Hubble's main camera is back at work).
The new problem, however, is "totally different", says Preston Burch, Hubble's mission manager at NASA's Goddard Space Flight Centre in Greenbelt Maryland, US. The power source itself seems to be working correctly – it is the HRC's electronics that appear to be at fault, he says.
Burch is optimistic that the ACS and even the High Resolution Channel itself will still be usable, although he stresses that the outlook could change as engineers obtain new information about the problem.
Still, the problem could mean that the HRC will be able to use only half of its normal field of view in future observations, Burch says. "We would have to take more observations to cover a given area [of the sky], but that's far from the end of the world for us," he told New Scientist.
Malcolm Niedner, deputy project scientist for Hubble at Goddard, agrees with that assessment. "None of us is talking about the loss of HRC," he told New Scientist. Losing half of the channel's field of view is being talked about as "a worst-case scenario," he says.
Hubble engineers have more tests to do over the next few days and Burch says he thinks they will understand the problem by the end of the week. "Our goal is to be back on the air doing ACS science next week, but we can't make any promises," he says.
Hubble is continuing to make observations with its other instruments in the meantime.
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