With the Hubble Space Telescope's new brain working and its sense of direction restored, astronauts went out on a final round of repairs Thursday before giving the $3 billion observatory back to space on Christmas Day.
Astronauts John Grunsfeld and Steven Smith floated out of space shuttle Discovery this afternoon to install a new radio transmitter and data recorder, as well as steel shields on Hubble's exterior to protect it from solar damage. Before going out, Grunsfeld had to switch spacesuits because of a power problem with his outfit. He ended up using a colleague's suit.
"Ah, John, another beautiful day outside," Smith said.
NASA's premier eye on the universe has been out of commission for the past month with failed gyroscopes. Two other spacewalks earlier this week were marathon sessions.
Astronauts Michael Foale and Claude Nicollier, hovering next to each other outside the Hubble, pulled out the telescope's outdated computer Thursday and stuck in a newer, faster model.
"The brains of Hubble have been replaced," Grunsfeld announced from inside the shuttle Discovery as the two spacewalkers completed the job.
The installation of the new $7 million computer -- actually, three interchangeable computers, only one of which runs at any given time -- fell to Foale, a software programming whiz. He had to be extra careful not to bend the approximately 1,000 fragile, gold pins in the computer cables.
Once it was snapped into place and the connections checked, "the computer just took over, and we've been using it ever since," said Hubble program manager John Campbell. "It seems to be running perfectly well, just without a hitch."
While ancient by modern desktop computer standards, the Hubble's new Intel 486 processor is a big step up from its old Intel 386. The telescope's new nerve center is 20 times faster with six times the memory.
"We have a brainier Hubble Space Telescope than we have ever had before," said David Leckrone, a senior Hubble scientist.
Leckrone said the speedier computer will help improve Hubble's ability to track moving objects and should increase its already powerful aiming capabilities.
To that end, the astronauts on Thursday replaced one of the Hubble's three guidance sensors. The refrigerator-sized instruments help the Hubble gain its sniper's aim on distant stellar objects.
During their grueling eight hour, 15-minute spacewalk on Wednesday, the second-longest in NASA history, astronauts replaced Hubble's six gyroscopes with new units needed to revive the broken telescope.
It hasn't been a mission for short space walks: Thursday's was eight hours, 10 minutes long.
But unlike Wednesday's space walk, when stubborn bolts and a hard-to-close lid slowed things, Nicollier and Foale basically stayed on schedule. There was momentary concern when Mission Control noticed a spike in the carbon dioxide insid Nicollier's spacesuit, but it turned out to be a faulty reading.
The telescope shut down on Nov. 13 when too many gyroscopes failed. After it is freed into orbit on Saturday, astronomical observations should resume in two weeks.
The shuttle is due back on earth Monday. NASA wants Discovery down well before New Years' Eve, to avoid any Y2K computer problems.