Wearing gloves about as nimble as fingerless winter mittens, the astronauts then had to unscrew eight tiny bolts without allowing the fasteners or handheld tools to float off into weightless space, perhaps damaging NASAs fragile flagship telescope.
Identical tasks often frustrate master mechanics on Earth. "But just imagine doing it with spacesuit gloves on," said Calvin Seaman, NASAs lead spacewalk integration engineer for the Hubble rescue mission.
And as it turned out, one of the spacewalkers specially designed tools nearly got away from Grunsfeld
"Uh-oh," Grunsfeld said as he scrambled to snatch a seven-inch socket that inadvertently popped off a battery-powered wrench and began floating off into open space.
"Im just going to hold it here until Steve gets back if thats okay," Grunsfeld said as Smith, his spacewalking partner, scurried over to help.
"Im almost there," Smith said. "Stand by."
"Im in no hurry," Grunsfeld replied. "In fact Im holding it with two hands now."
Watching on from inside Discoverys crew cabin, astronaut Michael Foale added: "Im sure youll keep a hold of it."
Grunsfeld did. And once the socket was safely tucked away in a tool caddy, he and Smith waltzed through the rest of the job, which was the first major chore on the third and final spacewalk scheduled on Discoverys planned eight-day mission.
The spacewalking duo first removed an old transmitter that was designed to last 15 years but inexplicably failed after eight. Hubble consequently had been relying on a single back-up transmitter since 1998.
Then they hooked up a new transmitter equipped with wing nuts that are infinitely easier to fasten and unfasten in a zero gravity environment. And with that done, they moved on the rest of their work, which included:
- Replacing a 1970s-style reel-to-reel tape recorder with a new digital solid state recorder.
The old and new recorders both are capable of storing science data until it can be beamed back to Earth via satellite. But unlike the old mechanical device, the new recorder is considered less prone to failure. It has no reels, no tape and no moving parts. It also can store 10 times as much data as the old mechanical recorder.
- Outfitting parts of the telescope with a new metallic skin.
A decade in space has taken a harsh toll on Hubbles skin multi-layer insulation that protects the telescope and its instruments from extreme and rapid temperature changes the observatory is exposed to as it circles around the sunlit and dark sides of Earth.
Some of the insulation is torn and cracked particularly in areas exposed to the sun. So Smith and Grunsfeld equipped parts of Hubble with new covers made of a specially coated stainless steel foil.
The covers which look like oversized cookie sheets were custom-made to fit over the doors of bays that house sensitive telescope electronics.
In order to do the job, Smith and Grunsfeld first stripped away shiny, makeshift insulation that was jury-rigged to the telescope during a February 1997 servicing mission. The old insulation was stuffed into a bag so it can be disposed of back on Earth.
The work, meanwhile, obviously put the spacewalkers in a cheerful holiday mood.
"I feel like a kid going in to get toys out of Santas bag," Grunsfeld said as he filled the trash sack.
"Tonights the night!" Smith replied.
In the midst of the cosmetic makeover, the high-flying shuttle and its crew provided a nighttime skyshow for stargazers across the southern U.S., including those near NASAs Johnson Space Center in Houston and Kennedy Space Center here.
"Discovery, Houston, you sure made a beautiful star in the heavens as you passed right over us just a minute or two ago," astronaut Steven Robinson radioed up to the crew from NASAs Mission Control Center in Houston.
A scant two minutes later, the winged spaceship streaked over its coastal Florida homeport, where the crew launched last Sunday.
"Were over Florida at this time," Foale told the spacewalkers. "If you look up, youll see Florida in its full glory."
When all was said and done the spacewalkers only had time to install two of the specially designed equipment bay covers during what turned out to be about an eight-hour spacewalk.
The original plan called for six covers to be attached to the tubular telescope, but the work was considered a low-priority for Discoverys flight. The remaining four will be fixed to the outer shell of the observatory during a servicing mission now scheduled for launch in the spring of 2001.
Smith and Grunsfeld set out on the cargo bay excursion about 2:17 p.m. EST as Discovery flew high over the deep blue Pacific Ocean near the coast of the Australian continent.
"Ah John, another beautiful day outside. Christmas Eve working on the Hubble Space Telescope," said Smith, payload commander and chief spacewalker on the mission.
"Look at that Earth!" Grunsfeld marveled. "Oh, beautiful."
Smith was wearing crewmate Foales spacesuit because the batteries on his bulky outfit did not charge adequately before the astronauts set out on their first order of business: Wiring up an electronics device designed to make the telescopes three Fine Guidance Sensors operate more efficiently.
Shaped like baby grand pianos, the 500-pound sensors give Hubble the ability to remain locked onto an astronomical target for days at a time. The resulting stability can be compared to holding a laser beam on a dime that is 200 miles away, or the distance between Washington, D.C. and New York City.
Foale and Swiss astronaut Claude Nicollier installed a $13 million refurbished guidance sensor during an 8-hour, 10-minute excursion Thursday.
Foale, who was directing the highly choreographed spacewalk from inside the shuttle, told the spacewalkers at one point to make sure they were securely tethered to the 13-ton observatory. Spacewalkers routinely use extra-strong safety tethers to make certain that arent cast adrift in open space.
"I recommend that you always be positively tethered to the telescope as much as you can," Foale, who survived a near-deadly June 1997 cargo ship crash at Russias Mir space station, told the two spacewalkers.
"You can definitely recommend that," Smith said.
The wiring job went without a hitch, and Hubble project officials reported that the new electronics gear was working as advertised.
"Were very impressed with Dr. Grunsfelds and Steve Smiths work," astronaut Steven Robinson radioed up to Discoverys crew from NASAs Mission Control Center in Houston. "You guys are batting 1,000."
During an opening act earlier this week, Smith and Grunsfeld successfully repaired Hubbles troubled pointing control system, which failed Nov. 13, halting some 100 astronomy projects being conducted by researchers around the world.
Foale and Nicollier outfitted Hubble with a new computer brain and the refurbished guidance unit during a second spacewalk Thursday.
With the last of the cargo bay forays now finished, NASA flight directors declared victory as the crew got ready to head into the home stretch of what many considered an emergency mission.
"That puts us in the status of full mission success," Robinson told the astronauts as they prepared to get back aboard the shuttle.
"We are very privileged and grateful to have taken part in the great endeavor to reestablish Hubbles astronomy capability," replied Foale, a British-born astrophysicist.
"We are very grateful again - to be rounding off this year with such a tremendous achievement."
"Discovery, thanks for the words," Robinson said. "Were having a great Christmas Eve."
Finally fully-functional after six weeks of scientific silence, the worlds most powerful and productive astronomical observatory is to be released from the shuttle at 6:03 p.m. Saturday.
Another week or two of post-repair testing is scheduled, but Hubble is fully expected to be back in business by the first or second week of the new millennium.
Discovery and its seven-member crew will spend the last full day in space Sunday preparing their ship for a return to Earth.
The $2 billion shuttle is scheduled to land at the Kennedy Space Center's three-mile runway at 5:24 p.m. Monday.
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