The docking ports of Discovery and station come together above the South Pacific. Photo: Spaceflight Now/NASA TV

The shuttle Discovery glided to a delayed-but-successful docking with the international space station early today to deliver the first of three new crew members after flight controllers finally managed to lock down a possibly free-swinging solar panel.

Approaching from directly ahead of the space station at a glacial tenth-of-a-foot per second, Discovery's docking system engaged its counterpart on the front of the Destiny laboratory module at 1:38 a.m. as the two spacecraft sailed 236 miles above the south Pacific Ocean east of New Zealand.

"Houston, ISS, we have capture light," shuttle astronaut Andrew Thomas radioed.

"Docking confirmed," said NASA mission control commentator Rob Navias.

Two hours later, after leak checks and work to resolve communications problems on the ground, a final hatch was cranked open at 3:51 a.m. and station commander William Shepherd, Yuri Gidzenko and Sergei Krikalev welcomed Discovery skipper James Wetherbee and his crew on board with enthusisatic hugs and handshakes.

Clearly enjoying themselves in the roomy Destiny laboratory module, the astronauts cavorted and tumbled about, taking a moment here and there to look out the lab's bay window at the blue-and-white Earth passing by below.

Looking on like a proud father, Shepherd floated near the lab's forward port to Discovery, smiling as his replacement, Russian commander Yury Usachev, a Mir veteran, turned somersaults in the lab's central aisle.

The primary goal of the 103rd shuttle mission is to replace Shepherd and his crewmates - Yuri Gidzenko and Sergei Krikalev - with Usachev, James Voss and Susan Helms.

"Our kudos to the entire crew of Discovery," astronaut Gerhard Thiele radioed from Houston a few minutes after hatch opening. "And welcome to Yury, Susan and Jim in their new home."

The shuttle also is carrying some five tons of equipment and supplies in an Italian-built pressurized cargo module mounted in the ship's cargo bay. The module will be attached to the station overnight Sunday, unloaded and re-berthed aboard Discovery late next week for return to Earth.

The major item on the agenda this morning was to transfer Usachev's Soyuz seat liner and spacesuit from Discovery to the station. The work was completed by 5:34 a.m. and with his custom seat liner now in place aboard the station's Soyuz lifeboat, Usachev is officially a member of Shepherd's crew, replacing Gidzenko.

Gidzenko, now a member of Discovery's crew, will sleep aboard the shuttle from this point forward and Usachev will bunk on the station. Voss will replace Krikalev Monday and Helms will officially move in Wednesday.

Flight director John Shannon said Shepherd will remain in command until hatches between the station and Discovery are closed for undocking on March 17. But that is strictly a technicality and for all practical purposes, Usachev will assume command when Shepherd begins sleeping aboard Discovery. The Expedition 2 crew's station tenure will not officially commence, however, until the hatches are closed prior to undocking.

In the near term, Voss and Helms plan to begin a seven-hour spacewalk at 11:47 p.m. this evening to install equipment on Destiny's hull to support installation of the station's Canadian-built robot arm during a shuttle visit next month.

They also will disconnect power cables between the station and a shuttle docking port on the Unity module's downward-facing, or nadir, hatch.

Thomas, operating Discovery's robot arm, then will move the docking port to Unity's left-side hatch to clear the way for attachment of the Leonardo cargo carrier on the nadir port overnight Sunday.

In preparation for the spacewalk, hatches between Discovery and the station were closed at 5:54 a.m. to allow the shuttle's cabin air pressure to be lowered from 14.7 pounds per square inch to 10.2 psi.

Today's docking originally was planned for 12:34 a.m. But Discovery's final approach was held up when flight controllers failed to receive indications that one of two huge U.S. solar panels on the station had locked in place as required.

NASA flight rules called for the station's P6 solar panels, which stretch 240 feet from tip to tip, to be locked in position for shuttle dockings to prevent possible damage from structural loads imparted by the orbiter at contact.

Securing the arrays also prevents potential unwanted movement caused by exhaust plumes from the shuttle's maneuvering jets during final approach under some thruster failure scenarios.

As Discovery closed in on the space station Friday evening, four Russian solar arrays and the port wing of the P6 array (as viewed from the shuttle) were feathered edge on and locked in place as planned, but flight controllers were not able to confirm the status of the P6 starboard array (again, as viewed from the shuttle).

Wetherbee, meanwhile, completed his approach and took up position on the velocity vector, or "v-bar," 400 feet or so directly ahead of the station while engineers discussed solar array fixes on the ground.

Station flight director Rick La Brode told reporters later the problem involved one of two latches on the array's gimbal mechanism.

Only one such latch is needed and flight controllers elected to use latch No. 2, which had never been used before, for Discovery's docking. The latch drew current, La Brode said, but failed to drive closed.

Flight controllers then decided to open latch No. 2, move the array slightly and attempt to engage latch No. 1, which has been used in the past. This time, the array locked in place as required and Wetherbee was cleared to begin the final push to docking.

"Discovery, Houston, configure for docking and 'go' for V-bar approach," Thiele radioed from mission control a few minutes past 12:30 a.m.

"Copy, configure for docking and go for V-bar approach," astronaut Paul Richards replied.

"And Discovery, Houston, by the way, the arrays are locked. Verified locked," Thiele called.

"Copy, Houston, that's good news."

The space station as seen by Discovery during the rendezvous. Photo: Spaceflight Now/NASA TV

With Discovery oriented with its tail pointing toward Earth and its cargo bay facing the station, Wetherbee began inching toward the outpost, moving with deliberate caution to maintain the proper alignment.

"You have a great looking ship there, Capt. Shepherd," Wetherbee radioed as Discovery approached.

Once Discovery and the station were locked together, the P6 arrays were once again released to resume tracking the sun and the shuttle began controlling the orientation of the combined spacecraft. Control later was transferred to the station's gyroscopes.

The post-docking work was carried out successfully, despite an apparent computer glitch at NASA's White Sands, N.M., satellite control center that knocked out all voice and telemetry between mission control and the space shuttle for 34 minutes.

Space station controllers were able to relay commands through Shepherd to the shuttle crew until communications could be restored.

Despite the delay in docking and Wetherbee's unplanned stationkeeping while the solar array issue was resolved, the shuttle commander was able to save 40 pounds of propellant in Discovery's nose tanks and 40 pounds in the aft over what was predicted before launch for a normal rendezvous and docking.

"You saved us 80 pounds of prop, despite the fact that we were 40 minutes hanging out in front of the station at 450 feet," Thiele radioed. "You couldn't have done better."

"We couldn't have done it without your help," Wetherbee replied. "The shuttle is a superb flying vehicle, it makes it relatively easy. We're glad we were able to save some prop, maybe we can use that to boost the station up a little bit higher."

Shannon said the saved propellant will, in fact, be used to help increase the space station's altitude later in the mission during three one-hour reboost sessions.