"We are really ready to go back to business," said Anne Kinney, a senior astronomer at NASA headquarters in Washington, D.C. "And we're really delighted to be going into the new millennium with a fully operational telescope."
"I'd mark today as a great success for the Hubble repair mission," added NASA lead flight director Linda Ham. "The crew did just an excellent job. They kept up with everything we asked them to do."
The high-priority repair work kicked off about 1:54 p.m. EST as Smith and Grunsfeld floated out of the shuttle's airlock hatch. The 122-foot-long winged spaceship was cruising more than 360 miles above the eastern coast of Australia at the time.
Snatched out of orbit Tuesday, Hubble loomed four stories tall atop a turntable-like servicing platform as the spacewalkers moved out into Discovery's expansive cargo bay.
"Ok, John. You ready to go," asked Smith.
"Ready to go," Grunsfeld replied.
Added Smith: "Hubble needs us."
Clad in cumbersome spacesuits, the astronauts faced an extreme but visually stunning work environment.
With Discovery circling Earth once every 97 minutes, Smith and Grunsfeld saw five sunrises and just as many sunsets as the shuttle repeatedly passed from the sunlit to the dark side of the planet. Temperatures in the cargo bay, consequently, fluctuated between 250 degrees Fahrenheit and minus 250 degrees Fahrenheit.
The view from above, meanwhile, was panoramic: Below cloud-speckled skies the astronauts could see rugged brown continents and deep blue oceans.
"Ah, beautiful sight out here. Beautiful day," said Smith.
The job at hand: Repairing Hubble's failed pointing system, which is designed to steady the observatory so it can precisely point at stars, planets, galaxies and other celestial objects.
Crucial to the system is a set of six gyroscopes. Housed in three metal boxes the sizes of toasters, the devices are located within a pantry-like equipment bay near the base of the observatory.
Edging his way into the heart of the $3 billion observatory, Smith removed the first of the gyroscope boxes. Lying on his back like an auto mechanic, he was forced to work within inches of three crucial but fragile star trackers, which also play a key role in precision pointing.
"It's a real tight fit for Steve inside the telescope," said Joe Tanner, an astronaut and veteran Hubble spacewalker on standby at NASA's Mission Control Center. "He needs to work his body around in that small space without touching (the star trackers)."
Once the first set of gyroscopes was removed, the astronauts had a bit of trouble packing it away in a cargo bay storage container. The tight fit surprised Smith.
"Got some curveballs; got some knuckleballs today," he said.
Smith and Grunsfeld then removed and replaced the other two gyroscope boxes while engineers at the Goddard Space Flight Center tested the new units to make certain they are working properly.
They are, and Hubble project scientists are understandably ecstatic.
"This was really a great day for Hubble," said Kinney. "For us, the real big deal was the gyros. We've got the (new) gyros in now, and we're ready to go back to business."
The successful repair was especially gratifying for Kinney and other NASA scientists, who have suffered through a bleak year that included the loss of both the Mars Climate Orbiter and the Mars Polar Lander spacecraft.
"Up until now it has been a tough year for space science," Kinney said. "We're really delighted to have the shuttle mission to the Hubble Space Telescope go so beautifully."
The gyroscope swap - which took about four hours to complete - was just the first of three chores Smith and Grunsfeld set out to complete during Wednesday's spacewalk.
The astronauts serviced a pair of valves on an instrument cooling system. The idea was to vent nitrogen coolant from an infrared camera that has been out of commission since January.
The last chore involved installing six voltage regulator kits designed to keep the telescope's batteries from overcharging and overheating. And when all was said and done, Smith and Grunsfeld approached a spacewalking endurance record.
"Absolutely fantastic job today," astronaut Steven Robinson radioed up to the crew after the 8 hour, 15 minute excursion. "We're very pleased with everything you've done and you deserve a good rest tonight."
"It was a long day, but we're very pleased that we achieved so much," replied mission specialist Michael Foale, who directed the highly choreographed spacewalk from inside the shuttle's crew cabin. "I think Steve and John especially deserve a big hand."
The only longer outing: A dramatic 8-hour, 29 minute satellite rescue during which three astronauts manually grabbed a stranded communications spacecraft so it could be rocketed up to its intended orbit 22,300 miles above Earth.
That walk was carried out in May 1992 aboard shuttle Endeavour's first voyage into space.
Still to come on the planned eight-day flight: Two more spacewalks scheduled to begin at 2:50 p.m. Thursday and Friday, respectively.
Spacewalkers Claude Nicollier and Michael Foale will outfit Hubble with a new $7 million flight computer and a $13 million refurbished guidance sensor during the second foray.
Smith and Grunsfeld will install a new science data recorder and a replacement for a failed radio transmitter during a third and final spacewalk.
Barring any unforeseen problems, the astronauts will re-launch Hubble from the shuttle's cargo bay about 6:03 p.m. Christmas Day. Discovery and its seven-member crew are due back at the shuttle's Florida homeport at 5:24 p.m. Monday.
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