One week after two anomalous events caused a snag in NASA's attempt to revive the Hubble Space Telescope, the orbital observatory is nearly back up and running, with science operations set to resume this weekend.
"We are up to the same place we were at about 8 o'clock Wednesday night of last week," with the telescope control systems running, but its instruments still in safe mode, said Art Whipple, manager of the Hubble Systems Management Office at NASA's Goddard Space Flight Center in Greenbelt, Md.
The new glitches cropped up while engineers were attempting to switch to a backup data relay channel in the 18-year-old observatory's Science Instrument Control and Data Handling system after the primary channel failed on Sept. 27.
The primary channel, called Side A, had until then been working properly since the telescope launched in April 1990. The data relay channels allow the spacecraft to send its images of the cosmos back to Earth.
The switch to the backup channel, called Side B, was a tricky maneuver that required the activation of five other backup systems that had also been in hibernation since Hubble's launch.
The maneuvering "just made the timing too tight," Whipple said in a Thursday teleconference.
One of the glitches occurred when a component of Hubble's main camera returned a lower than normal voltage, while the other involved a communications drop between the spacecraft's main computer and the one that controls its science instruments, called the payload computer.
The glitches caused both the payload computer and the Side B data formatter to reset. The switch to Side B was, however, successful, and as of 11:15 a.m. EDT (1515 GMT) Thursday, the payload computer was back up and running.
What exactly caused the reset is remains a mystery, Hubble managers said.
"We cannot know the exact cause, of course, because we cannot get to the hardware. All we can say is that it appears to have been to have been an electrical event," Whipple said, ruling out any software or commanding errors.
Whipple said that "it is possible that we may see another event of this type in the future."
Fortunately, the electrical event "does not appear to have done any permanent damage," Whipple said.
If the payload computer stays operational for the remainder of this week, the Hubble team will switch on the telescope's Wide Field Camera 2 and once more resume science operations.
The initial glitch with the Side A relay channel postponed the planned Oct. 14 launch of the space shuttle for its next, and last, Hubble repair mission until early 2009.
Every month that the shuttle mission to service Hubble is delayed costs NASA $10 million, mission managers have said.
When the astronauts do get up to Hubble, they hope to replace the tray that houses both Sides A and B.
The mission is also slated to install a new camera, replace gyroscopes and batteries, upgrade Hubble's guidance equipment and add a docking ring.
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