— The ACS's "discovery efficiency" for recording faint objects is three to four times higher at visible wavelengths than a new instrument, called WFC3, to be installed in 2008 (Illustration: STScI)
Astronauts should try to repair the main camera on the Hubble Space Telescope in the shuttle servicing mission set for next year, say some scientists involved with the Advanced Camera for Surveys, which failed on Saturday.
Famed for a series of spectacular photographs, including the Ultra Deep Field image of galaxies at the edge of the universe, the camera had been the busiest instrument on Hubble. More than two-thirds of proposals for the next allocation of Hubble time, submitted to NASA the day before the failure, asked for time on ACS.
Yet at a Monday press conference, NASA officials said repairs were too difficult to attempt during a planned shuttle mission in 2008 (see Hubble's main camera permanently hobbled).
They also said the telescope would have capabilities surpassing those of the ACS after it is repaired and upgraded with two new instruments, including one called the Wide Field Camera 3 (WFC3).
"WFC3 is a very powerful instrument, with capabilities ACS doesn't have," including very sensitive response in the infrared, acknowledges Garth Illingworth, deputy principal investigator for ACS and an astronomer at California's Lick Observatory.
"But what we were looking forward to was operating it in parallel with the advanced camera," he told New Scientist. The plan was for the two cameras to take turns observing the sky at different wavelengths, with ACS observing in the visible while WFC3 observed in the infrared.
With both instruments, Hubble would have been able to search the sky for faint young galaxies about 12 billion light years away. "It would have been amazing," he says. "It becomes much more challenging to do that with WFC3 alone."
In survey mode, ACS has both a wide viewing field and very high sensitivity, so it excels in recording faint deep-sky objects. The Space Telescope Science Institute, which manages Hubble, rates its "discovery efficiency" for recording faint objects as three to four times higher than WFC3 at visible wavelengths. The new WFC3 will nearly match that capability at infrared wavelengths, where ACS lacks detectors. But alone, WFC3 will need twice as much time to survey the deep sky.
In high-resolution mode, ACS includes the highest performance coronagraph that has ever been launched into space. By blocking light from the central star, it allows astronomers to search for evidence of planets and disks surrounding young stars. "Nothing else will replace this," Illingworth says.
Repairing ACS would also give NASA a back-up camera in case of problems with WFC3, Illingworth says. That would keep spectacular photos coming in the years between the 2008 servicing mission and the launch of the James Webb Space Telescope, now set for 2013.
"There's been a lot of really depressed astronomers [since ACS failed]," says John Blakeslee, an astrophysicist at Washington State University in Pullman, Washington, US. "If at all possible, it would be wonderful to have that capability back."