NASA does not believe it can restore the Hubble Space Telescope’s main camera to full operation following an electrical failure on 27 January, but it is not planning any changes to the Space Shuttle servicing mission already scheduled for September 2008.
The Hubble’s Advanced Camera for Surveys (ACS), used for about 70% of the telescope’s observations, stopped functioning when the power feed to its electronics package failed, NASA believes. The ACS had been operating on its backup power distribution system since an electrical failure in June last year.
“It is too early to know what influences the ACS anomaly may have on Hubble Space Telescope servicing mission 4 [SM-4] planning,” says programme manager Preston Burch. “But we do not see a desire or need for any change to the plans for SM-4.”
NASA believes it can get one of the ACS’s three detectors, the solar blind channel, operating again before the end of February, “but we are not optimistic at all that the other two [wide-field channel and high-resolution channel] can be restored,” he says.
Hubble’s wide-field planetary camera, near-infrared camera, multi-object spectrograph and fine-guidance sensors are still operating, but loss of the ACS’s two main channels will force a redirection of the observations the telescope can perform.
Astronomers had submitted their proposals for the next cycle of Hubble observations only the day before the failure, and NASA says will now have to go back to them for revised proposals. A set of contingency non-ACS science programmes selected in November after the last failure will now inserted into the schedule, the agency says.
Installed during a Hubble servicing mission in 2002, the ACS was about a month short of its five-year design life when it shut down. The camera’s primary electrical system – called Side A – failed in June last year, but NASA was able to switch to redundant electronics on Side B and restore all three channels by July. There was another brief interruption in September.
NASA says the Side B electrical system shut down on Saturday morning when a current spike triggered a fuse. “The fuse did what it was supposed to do – it saw a high current and popped,” Burch says, adding the failure was isolated to the power distribution unit supplying ACS Side B, and does not threaten other Hubble sensors.
Burch says the inaccessible location of the ACS main electronics box on Hubble, and the full schedule of spacewalks already planned for the servicing mission, makes it unlikely NASA will change its plans for SM-4. The new wide-field camera and other sensors to be installed in 2008 will more than overcome the loss of the ACS, he says.
“There is not much opportunity to accelerate SM-4,” says Burch, adding that the additional effort and money required to develop the hardware and tools to replace the ACS “does not look very attractive”.