The iconic but elderly Hubble Space Telescope appears to have been resurrected again after a shutdown of more than a month following a computer glitch. Science has learned that following a switch from the operating payload control computer to a backup device over the past 24 hours, Hubble’s operators have re-established communications with all the telescope’s instruments and plan to return them to normal operations today.
“Hubble is back!” Tom Brown, head of the Hubble mission office, emailed to staff at the Space Telescope Science Institute at 5:56 a.m. “I am excited to watch Hubble get back to exploring the universe.”
The problems started on 13 June when the payload computer that controls the science instruments and monitors their health spotted an error in communications with the instruments and put them into safe mode. Hubble’s operators initially thought a memory module was at fault but switching to one of three backup modules produced the same error. Various other devices were investigated and ruled out as the problem when the error persisted.
It was eventually decided that the entire Science Instrument Command and Data Handling (SIC&DH) unit, of which the payload computer is part, should be switched over from the currently operating instrument to the backup. Staff practiced the procedure with hardware on the ground over the past week and a full review was carried out to ensure it could be done without harming the telescope in other ways. Shortly before the switch was started yesterday, NASA announced it had identified the power control unit (PCU), which is part of the SIC&DH, as the source of the problem. The PCU supplies a steady voltage supply to the payload computer and it was either supplying voltage outside the normal range or the sensor that detects the voltage was giving an erroneous reading. Because there is a spare PCU as part of the SIC&DH, the switch went ahead.
Brown told his colleagues this morning that “Hubble was successfully recovered into Normal Mode on Side A of the [SIC&DH]. This marked the first time we were able to progress beyond the problem we were seeing on Side B.” He said that if all continues normally, Hubble will restart science observations this weekend.
Astronomer Richard Ellis of University College London, who was talking with Science when the news came in, says: “You have to tell everyone how nervous we all were!” The telescope, he says, has always been “a truly global facility. Everyone is a friend of Hubble. It’s unique.”