Spacewalking astronauts from the shuttle Atlantis tried on Sunday to revive a defective instrument on the Hubble Space Telescope used to discover black holes and other galactic phenomena, Reuters reported.
Like Hubble's advanced camera, which was rewired during a spacewalk on Saturday, the Space Telescope Imaging Spectrograph was not designed to be overhauled in space.
The device, known by the acronym STIS, splits light into its component wavelengths. It was shut down in 2004 after electronics problems cut off its power.
Buoyed by Saturday's successful spacewalk, astronauts Michael Massimino and Michael Good floated out of Atlantis' airlock just before 10 a.m. EDT/1400 GMT with high hopes of repairing STIS too.
"At this point we're feeling really good," Hubble project manager Preston Burch told reporters after Saturday's work.
Sunday's foray was the fourth of five spacewalks to upgrade the world-famous telescope for another five to 10 years of operation. Atlantis' mission is the fifth and final servicing call to Hubble before the shuttle fleet is retired next year.
Atlantis' crew have already installed two new science instruments, replaced Hubble's steering system and half its batteries, and repaired the advanced camera.
Engineers tested the camera overnight and found that one of its three channels was not restored.
It appeared "down for the count," said NASA mission commentator Josh Byerly. But Burch said that this only partial recovery of the camera was not unexpected.
NASA only had time and resources to rewire one part of the camera and scientists' chose the more popular wide-field mode.
"We would have liked to have a done a similar thing with the high resolution channel," Burch said.
But the scientists were not complaining.
With the refurbishments already accomplished, NASA is close to fulfilling its goals for the mission, with only the installation of another three batteries remaining. That job is scheduled for the mission's last spacewalk on Monday.
"They've made huge strides in restoring the health of the observatory," Burch said.
Recovering STIS would be a bonus.
"STIS is not a Spartan instrument. It had many bells and whistles, all of which have been proven to be valuable to many types of science," said Hubble project scientist David Leckrone.
The instrument was used, for example, to survey galaxies for black holes. It also made the first measurements of the atmosphere of a planet in another solar system.
On Saturday, astronauts installed the Cosmic Origins Spectrograph, which will use the light from distant quasars, or star-like celestial objects, to study the web-like gas and dust between the galaxies.
"It's very difficult to think of a project in spectroscopic astrophysics that you could not do with these two instruments," Leckrone said.
Hubble's observations have reshaped scientists' understanding of how galaxies form and change over time, of planet origins and of the mysterious "dark energy" force that is inflating the universe at a faster and faster rate.