Baltimore ? Two thirds of the observation ability on the popular Hubble Space Telescope’s main camera have been permanently lost following power supply problems, NASA announced Monday.

The Advanced Camera for Surveys shut down again over the weekend, the third outage in less than a year for the instrument. The orbiting observatory entered a protective “safe mode” Saturday morning and an initial investigation has determined that its backup power supply failed, the space agency said.

Observations are expected to resume this week using the Hubble’s other instruments. One of the three cameras on the ACS, the solar blind channel, is expected to be returned to operation, possibly by the middle of February.

The outlook is not good for the other two, said Dave Leckrone, a senior scientist on the Hubble Space Telescope project at the Goddard Space Flight Center in Greenbelt.

“We’re not optimistic at all that those will be restored,” Leckrone said.