CAPE CANAVERAL, Fla. -- Shuttle Discovery closed in on the International Space Station Saturday as its crew of astronauts and cosmonauts readied the ship for a weekend rendezvous at the 17-story outpost.

Docking Sunday

Shuttle Discovery's twin orbital maneuvering engines will be fired just after noon EDT (1600 GMT) Sunday, propelling the ship toward a docking at the International Space Station a little more than two hours later. Click here for live coverage.

With the shuttle and the station flying in formation in low Earth orbit, Discovery mission commander Scott Horowitz will dock the winged spacecraft at the outpost about 2:30 p.m. EDT (1830 GMT) Sunday.

The link-up will come two days after Discovery and four astronauts set sail from Kennedy Space Center with a new station crew, tons of fresh supplies and dozens of science research experiments.

And it will mark the beginning of a four-month stay for incoming station skipper Frank Culbertson and Russian cosmonauts Vladimir Dezhurov and Mikhail Turin, all three of whom were ecstatic to be in orbit.

"It's been eight years since I've been up here -- almost to the day -- and it feels like I just left," said Culbertson, a veteran shuttle astronaut who served a long stint in management before returning to space.

Added rookie Turin: "I'm having a great time here. The first impression was excellent."

The shuttle astronauts and their station-bound passengers spent their first full day in space preparing for the final stages of their rendezvous with the station, which is set to begin just after noon EDT (1600 GMT) Sunday with a firing of Discovery's twin orbital maneuvering engines.

The shuttle crew checked out trajectory sensors and a handheld laser device, rendezvous tools that will be used to gauge Discovery's range and rate of speed as the ship makes its final approach to the station.

They also tested a docking system camera and an associated docking ring that will latch on to an identical device on the station when the two craft link together. Shock absorber-like struts then will pull the two craft together to ensure an airtight seal between Discovery and the outpost.

With all that work done, the astronauts unlimbered Discovery's 50-foot (15-meter) robot arm, which will be used to mount a shuttle-borne shipping container to the station's U.S. Unity module.

More than three tons of food, clothing, supplies and research gear are to be unloaded from cargo carrier for Culbertson and his crewmates, who got a leg up on one of the 50 U.S. and Russian science experiments they plan to carry out during their expedition.

The trio performed an initial orbital run of a medical test aimed at gauging the effect of weightlessness on the spinal cord and muscular reflexes. The test will be rerun in five days and then again toward the end of the crew's four-month mission.

The station's current crew, meanwhile, spent the day packing up.

In space since March, outpost commander Yuri Usachev and flight engineers Susan Helms and Jim Voss will return to Earth aboard Discovery after 167 days in orbit.

The so-called Expedition Two crew caught a glimpse of their ride home -- or at least its exhaust plume -- after Discovery blasted off at 5:10 p.m. EDT (2110 GMT) Thursday.

"Jim, Susan and Yuri were able to see the smoke trail as Discovery lifted off," astronaut Ken Cockrell told Culbertson from NASA's Mission Control Center in Houston. "So they have physical evidence that you're on your way."

"We'll I'm sure that'll make them happy," Culbertson replied. "We're all happy here."

The Discovery astronauts plan to spend eight days moving the new crew in -- and the old crew out -- of the international station. Two spacewalks also are scheduled next week to mount coolant tanks and string power cables outside the station.

With Usachev, Helms and Voss on board, Discovery is scheduled to depart the station Aug. 20 and then land two days later. Culbertson and his crew will remain in space until Dec. 9.