January 30, 2007 1:44 PM PST
Hubble humbled by power failure
The Advanced Camera for Surveys, installed on the Hubble in March 2002, is considered the Hubble's "workhorse," according to Dave Leckrone, the senior project scientist on the Hubble Space Telescope.
About the size of a public phone booth, the scientific instrument consists of filters and dispersers that can sense wavelengths from ultraviolet to infrared on the light spectrum, and three electronic cameras.
The Hubble will still be able to function, but until a new camera is installed in 2008, the images will not be as far reaching.
The ACS' malfunction forced the Hubble to go into "safe mode" on Saturday, after some of its electronics essentially exploded, according to Leckrone.
"It really was a dramatic short circuit in the sense that it smoked and emitted gas. We detected that. Whatever short happened, it was nasty and it took down the fuse that is in the circuit that provides power to that side (side B) of the instrument," said Leckrone.
The ACS had been operating off the side B power since its side A electronics package malfunctioned in June 2006, he confirmed.
NASA took the Hubble out of safe mode on Sunday and will resume operations with the telescope's other instruments. The Hubble's Wide Field Planetary Camera 2, Near Infrared Camera Multi-object Spectrograph and fine guidance sensors can still work, according to NASA. WFPC2 should be operating by the end of the week, with the rest to follow next week, said Leckrone.
"We really regret losing ACS, and we put it onboard for good reason. But there is still a lot of great science that can be done, and it wasn't because the WFPC2 was in its shadow. We also have the NICMOS infrared camera, too," he said.
NASA also plans to have the ACS' Solar Blind Channel working from side A. The Solar Blind Channel provides data on hot stars, quasars and the weather systems and auroras on planets in the Earth's solar system.
The ACS' two remaining channels, however, are not reparable. And that is a big loss, according to Leckrone.
The ACS' Wide Field Channel had a field of view twice as wide as that of the WFPC2 and collected 4.5 times more light than any previous Hubble instruments, according to NASA specifications. Its High Resolution Channel allowed it to probe deep into galaxies with black holes, as well as offer high-resolution shots of the universe.
Those channels will not be fixed. A previously planned service mission on the Hubble to install a completely new camera was already scheduled for September 2008. The new camera, currently called the Wide Field Camera 3, will replace the downed WFPC2 and prove more powerful than the ACS was in most ways, according to Leckrone.
"A, the fuse is blown. There is no power. And B, even if we had power, we don't know what broke, so we wouldn't want to operate it," said Leckrone.
"In one particular wavelength, (ACS) was more sensitive than the new camera. But the new camera will far and away be better than the ACS taken as a whole. There is very little science that ACS could do that the new camera could not do. And there is a tremendous amount that ACS could not do that this camera will do. We have been planning for years for this camera," said Leckrone.
Until the WFC3 is installed, an alternative set of science programs will be NASA's focus for Hubble. After the June malfunction led scientists to anticipate the loss of ACS, the Space Telescope Science Institute collected alternative proposals.
NASA also extended last week's Friday deadline for the next round of Hubble proposals. Scientists who submitted proposals for using the ACS can submit entirely new proposals or modify their previous proposals to work with the WFPC2 and the remaining ACS Solar Channel.
ACS was a third-generation instrument and replaced the last original instrument left on the Hubble, which was launched into orbit on April 25, 1990, according to NASA. The Hubble's replacement, the James Webb Space Telescope, is set to launch in 2013.