Hubble's main camera hobbles back to life

October 2, 2006

David Shiga for NewScientist.com

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Hubble's most frequently used instrument, the Advanced Camera for Surveys (ACS), is partially functioning again, after shutting down unexpectedly last week.

Before it shut down on 23 September, the ACS was Hubble's most frequently used instrument. It uses three channels that are essentially three different cameras, and the problem began shortly after Hubble's managers attempted to switch power from the Solar Blind Channel (SBC) to the High Resolution Channel (HRC).

Despite the command to switch, Hubble's computer detected that power was not getting to the HRC and automatically shut down all three channels (see Hubble's key camera shuts down again).

Now, the camera's Wide Field Channel (WFC) has resumed observations, with the other two channels still offline. The WFC, the channel that had been used for most ACS observations, gets its power from an independent route that is not affected by the other two channels.

Switch issue :doh:

Hubble began taking observations with the WFC on Sunday. "The instrument seems to be performing nominally," says Preston Burch, Hubble's mission manager at the Goddard Space Flight Center in Greenbelt, Maryland, US.

Hubble engineers are now pretty sure that the problem with the other two channels is related to the mechanical relay that flips back and forth to send power to either the SBC or the HRC.

"All indications are that the commands [to flip] were properly received by the spacecraft, but we're not seeing the voltage [expected]," Burch told New Scientist.

There might be some dirt or debris that is preventing the switch from closing properly, he says. Another possibility is that the mechanism that moves the arms of the switch from one position to another is broken, he says.

Short circuit

Hubble's managers are thinking about trying to flip the switch back and forth, which could solve the problem by dislodging any dirt.

However, there is some worry that if the switch itself is broken, moving it could cause a short circuit that would kill the ACS's power source. A short circuit is considered an unlikely event, but it would make all three channels unusable, Burch says.

The Hubble team will meet on Wednesday to discuss what to do about the switch. "We're probably a couple days away from doing any on-orbit commanding of the hardware," Burch says.

If the switch problem cannot be fixed, the High Resolution Camera may still be able to make observations, but with only half its original field of view.