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 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) today, 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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