Zarya and Unity modules of ISS orbiting Earth. Photo: NASA

The Atlantis astronauts checked out the shuttle's three spacesuits early today, set up and tested a battery of rendezvous tools and generally readied the orbiter for docking early Sunday with the international space station. They also unlimbered Atlantis's 50-foot-long robot arm and spent a bit of extra time putting it through its paces to get a feel for the differences between simulators on the ground and the real thing. The arm will be used overnight Monday during a planned spacewalk by astronauts James Voss and Jeffrey Williams.

"The crew, from everything I could tell today, is chipper and doing great," said flight director Phil Engelauf. "They spent some extra time doing checkout of the RMS [robot arm]. We have several operators on board this flight who are qualified to use the arm, so we gave them a little bit more leeway in spending more time flying the arm to get a feel for that."

The only technical problem of any significance -- and it appears minor -- involves Atlantis's left-side orbital maneuvering system rocket. The two OMS engines are used for major orbital adjustments and for the critical deorbit rocket burn used to drop the shuttle out of orbit at the end of a mission. During a space station rendezvous rocket firing Friday, telemetry indicated one of two propellant shut-off valves in the left-side engine may have failed to close properly. The engine is still operational and flight directors do not anticipate any problems with the deorbit burn. But to be on the safe side, upcoming space station rendezvous burns will be carried out using the right-side engine only.

The crew is on schedule, the shuttle and its systems are "go" for docking and flight controllers are readying the international space station for the shuttle's arrival early Sunday around 12:31 a.m. EDT (0431 GMT).

"All systems on the ISS are performing well," said station flight director Paul Hill. "We're not chasing any anomalies besides the things we've already identified for repairs. We have started warmup on the FGB [Zarya module] and the [U.S. Unity] node. Both are progressing as planned. We've also started scrubbing the atmosphere inside the FGB and we'll start scrubbing the atmosphere inside the node after we get docked. Aside from that, the big thing on our plate will be activating the motion control system tomorrow about four orbits before docking. About an orbit after that, we'll go to the docking attitude and we'll wait for the shuttle crew to come up and dock."

You can follow the flight of Atlantis in Spaceflight Now's Mission Status Center. We will provide continuous play-by-play reports throughout the entire 10-day shuttle flight.