The international space station as photographed against Earth's horizon during a fly-around by shuttle Atlantis last month. Photo: NASA

Streaking through space at five miles per second, the shuttle Discovery gently docked with the international space station today as the two spacecraft sailed 240 miles above Ukraine. Commander Brian Duffy had no problems pulling off an on-time linkup at 1:45 p.m., despite the loss of Discovery's rendezvous radar.

"And Houston, Discovery, we have capture lights," one of the crew members called down as the two spacecraft bumped together.

A KU-band communications system failure Thursday prevented Discovery's crew from beaming down live television of the docking, but NASA carried grainy black-and-white views from a Russian TV camera mounted on the station's hull that showed the shuttle's final approach.

Still images downlinked through Discovery's S-band communications system also showed snapshots of the rendezvous from the shuttle crew's perspective and videotape of the docking will be downlinked later today when the shuttle passes over U.S. ground stations.

Despite the less-than-dramatic imagery, lead flight director Chuck Shaw said Duffy and company pulled off a textbook rendezvous, using only a slight amount of extra propellant without the benefit of the rendezvous radar system.

"We had a very good day today," he said. "We successfully rendezvoused and docked with the international space station. The rendezvous went extremely well.

"The propellant that we used for the rendezvous was only slightly greater than expected, further confirmation that our loss-of-radar procesures work just fine," he said. "The docking went perfectly. So all the procedures worked just fine and now we are ready tomorrow to actually start doing some good construction work on the station."

To get ahead of the timeline, the Discovery astronauts were cleared to enter the station's Unity module later this evening to transfer equipment needed by the station's first full-time crew.

With Discovery's KU-band system out of action, mission control will have to rely on the shuttle's slower S-band system to send up messages and notes to the crew for the remainder of the flight.

That same system will be used to beam down occasional still images from the shuttle's TV cameras. The only live television will occur during infrequent passes over U.S. and Russian ground stations.

Shaw said the difference between the KU- and S-band systems is similar to the difference between a 56K modem and a high-speed DSL or cable connection to the internet.

The S-band is "a little slower," he said. "We get spoiled with this high data rate stuff."

Indeed. While Shaw has dismissed the loss of realtime TV as a "minor irritant," it is a major disappointment to just about everyone else.

But the closed-circuit television system aboard the shuttle is working fine - it's the KU-band link to Earth that's broken - and today the astronauts simply used the ship's optical star trackers and laser range finders to obtain the navigation data they needed to complete the rendezvous.

Trailing the station by about nine miles, Duffy and pilot Pamela Melroy fired Discovery's maneuvering jets at 10:09 a.m. to begin the terminal phase of the rendezvous.

"And Houston, just for your info, Jeff (Wisoff) and Bill (McArthur) have been watching the station from the back with the binoculars," Duffy reported shortly before the burn. "They say it looks great."

"Thank you for the update," replied astronaut Ellen Ochoa from mission control. "And since we've had no joy on the rendezvous radar, we'd like to have you go ahead and take the KU select switch to GPC. ... That'll help get us set up for the star tracker pass."

For docking, the station was oriented vertically with respect to Earth with the Russian Zvezda module and a Progress supply ship facing the planet below and the U.S. Unity module facing deep space. The Russian-built NASA-financed Zarya propulsion module is sandwiched in between.

The imaginary line connecting the station to the center of the Earth is called the radius vector, or "R bar." By convention, points below the station are considered positive while those above it are considered negative.

Similarly, the line marking the station's orbital path is called the velocity vector, or "V bar." The positive V bar is in front of the station as it moves through space while the minus V bar is behind it.

As with all space station dockings, Discovery approached from behind and below, reaching the plus R bar and passing about 600 feet directly below the outpost just before noon.

The docking ring on Discovery was extended yesterday. Photo: NASA TV

Duffy then guided the shuttle up in front of the lab complex, reaching the plus V bar directly in front about 15 minutes later. The slow loop continued until Discovery was poised some 250 feet directly above the station on the minus R bar.

"I think the most interesting part about it is the way that we approach the station," Melroy said in a NASA interview. "We actually come at it from underneath. And then we will fly all the way around it until we're on top of it.

"And that'll be wonderful! To look down at the station, with the Earth behind it! Oh! I mean, wonderful pictures. I just can't wait to see it. I think it'll be really fantastic!"

The rendezvous was timed to set up a docking as the two spacecraft passed into range of a Russian ground station, which relayed critical telemetry to the Russian mission control center near Moscow.

Russian flight controllers usually use their ground stations and domestic satellites to relay commands to the station from Moscow to deactivate the station's motion control system to prevent any unwanted movements during the final phase of docking.

But because of heavy domestic traffic and other factors, the Russians instead planned to send up commands through NASA's communications network to the U.S. Unity module. The commands then could be routed to computers in the Zvezda module.

To ensure the proper timing for docking, Duffy held Discovery at a distance of 170 feet or so directly above the station for about an hour beginning just after noon. Around 1:15 p.m., he resumed the approach, stopping again at 30 feet for a few minutes to ensure docking took place within range of the Russian ground station.

"The reason the timing's important is because we want to be docking with the station while we're over a Russian ground site," Duffy said in a NASA interview. "So, we have a limited window that we want to be docking within.

"Staying on the profile and being in the right place at the right time with everything ready to go will be, you know, a bit of a challenge."

Animation shows the Z1 truss mounted to the Unity node using Discovery's robot arm. Photo: NASA TV/Spaceflight Now

But he had no problems and Discovery's docking system engaged hooks and latches on a pressurized mating adapter connected to the Unity module's forward hatch at 1:45:15 p.m. as the spacecraft passed over the Ukraine.

After leak checks, hatches between the shuttle and station were to be opened and the astronauts planned to float inside the roomy Unity node around 4:47 p.m. to begin moving equipment inside.

The goal of the 100th shuttle mission is to install a new $20 million docking port that will be needed later in the assembly of the station and a $273 million truss housing four stabilizing gyroscopes.

The 18,300-pound Z1 truss also will serve as a temporary mounting point for a huge set of U.S. solar arrays scheduled for attachment in early December.

On Saturday, Japanese robot arm operator Koichi Wakata is scheduled to mount the Z1 truss to Unity's upward-facing, or zenith, hatch. The new shuttle docking port, called pressurized mating adapter No. 3, will be attached to Unity's Earth-facing, or nadir, hatch Sunday during the first of four back-to-back spacewalks.