The seven astronauts gather together on Discovery's flight deck. Photo: Spaceflight Now/NASA TV

The Discovery astronauts successfully checked out two spacesuits today, unlimbered the ship's robot arm, inspected the cargo bay and monitored a waste water dump to make sure such procedures pose no threat to the international space station.

Discovery is scheduled to dock with the space station at 12:34 a.m. EST (0534 GMT) Saturday after a two-day orbital chase. The primary goals of the 103rd shuttle mission are to deliver the station's second full-time crew and some five tons of supplies and equipment.

The astronauts carried out a rocket firing late Thursday to fine tune their approach and another, larger "burn" this morning.

Today's rocket firing raised the high point, or apogee, of Discovery's orbit from 171 statute miles to 228 miles and boosted the low point, or perigee, from 151 miles to 170 miles. The maneuver will put the shuttle about 46 miles behind the station at crew wakeup this evening.

Lead flight director John Shannon said so far, the mission is proceeding in textbook fashion with no technical problems of any significance. And that's a good thing, he said, because "we have three pretty ambitious days from here on out."

The docking ring on Discovery was extended overnight in preparation for the upcoming link up. Photo: Spaceflight Now/NASA TV

After docking, the astronauts will begin transferring critical equipment over to the station, including three Soyuz seat liners and spacesuits that will be used by the station's second full-time crew: Commander Yury Usachev, Susan Helms and James Voss.

The new crew will move aboard the station in staggered fashion, with Usachev transferring Saturday, replacing Expedition One crewman Yuri Gidzenko. The move will become official when Usachev's seat liner is in place on the station's Soyuz lifeboat.

Voss will replace Sergei Krikalev Sunday evening and Helms will replace Expedition One commander William Shepherd later next week.

In between spacewalks, the astronauts will attach an Italian-built pressurized cargo carrier to the space station.

The Leonardo module, making its first flight, is loaded with five tons of equipment and supplies, including the station's first suite of scientific experiments. It will be attached to the Unity module's downward facing node, unloaded and reberthed in Discovery's cargo bay for return to Earth.

Leonardo rests in Discovery's payload bay as seen from camera on the shuttle's robot arm. Photo: Spaceflight Now/NASA TV

Sergio De Julio, president of the Italian Space Agency, called the crew today to congratulate them on a successful launch.

"How is our baby, our Italian baby?" he asked.

"Very nice, very beautiful outside in the payload bay," said shuttle commander James Wetherbee. "It's sparkling silver, very clean looking of course. You have made a very nice module, a very great spacecraft.

"We are looking forward to going inside and working with it and for the first time, we'll be able to outfit the international space station with some experiments."

With the station rendezvous proceeding like clockwork, the astronauts spent the day today readying Discovery for docking and checking out the spacesuits Voss and Helms will use overnight Saturday.

"What the crew did today is they got out their spacesuits and ran them through all the checks to make sure they were working (and) they were working fine, we have two good spacesuits," Shannon said.

"They took out the robotic arm, did a good survey of the payload bay, did a checkout of all its backup systems. That worked out great.

"We parked the arm over the forward left side of the payload bay and took a look at a waste dump," he continued. "We did that in order to assure the (space station) program that the waste nozzle is installed correctly and there's no icing or ice formation on it.

John Shannon at today's daily news conference. Photo: Spaceflight Now/NASA TV

"When we're docked to the station and do waste dumps, we want to make sure that none of that ends up on the station. That could degrade the solar arrays over time. We looked at all that, it all looked really normal so we'll be clear to do waste dumps while we're docked."

The only problems encountered so far involve trouble with a cabin fan used as a supplemental air filter and a quickly-resolved glitch with one of the orbiter's computer displays.

The orbiter cabin air cleaner is a portable unit mounted in one of the two hatchways between the shuttle's upper and lower decks. A filter in front of the fan traps lint and other debris that manages to work its way into the air.

"We use all that blue Velcro and as you're pulling books and tabs and things off you create a little bit of blue lint and we find that on filters to avionics and things and the cabin air cleaner is a good way to pick up most of that," Shannon said.

"I think the biggest impact (of the fan's loss) is it's a good site for the lost and found, he said. "Whenever somebody loses a piece of paper or a card or their glasses or whatever, you can always find it on the (fan) screen because everything eventually ends up there."

The fan is not required, but engineers are developing a repair procedure that may recover its use.

The astronauts are scheduled to begin a seven-hour sleep period at 10:42 a.m. Wakeup is planned for 5:42 a.m. and if all goes well, Wetherbee and his crewmates will switch to their rendezvous flight plan around 7:12 p.m.

At 10:15 p.m., with the shuttle trailing the space station by about 9.2 miles, Wetherbee will carry out a rocket firing to begin the final approach.

"The orbiter right now is trailing and it's lower and that, of course, will allow us to catch up," Shannon said. "We'll come up and do the terminal initiation burn and that will phase us in about 400 feet below the station on what's called the r-bar."

The R-bar is an imaginary line connecting the space station to the center of the Earth. On the most recent shuttle visit last month, the orbiter proceeded directly up the R-bar to a docking with a port on the Unity module's downward facing, or nadir, hatch.

Illustration shows Discovery making its way to the V-bar. Photo: Spaceflight Now/NASA TV

This time around, Discovery will dock instead with a port on the forward end of the Destiny laboratory module, which faces the direction of the station's motion directly ahead along an imaginary line known as the velocity vector, or V-bar.

"We're going to dock with PMA-2 on the end of the lab," Shannon said. "So the crew puts in a computer controlled pitch maneuver while they're on the R-bar that rotates the orbiter 90 degrees up at about 0.1 degrees per second.

"When they initiate that maneuver, they do a plus-X firing with the translational hand controller that sends them out in front of the station," he said. "Meanwhile, the orbiter is pitching up. As they go out in front, they pick up orbital altitude and it phases them right up onto the V-bar."

At that point, Discovery will be oriented with its tail pointing toward Earth and its open cargo bay pointed toward the station and the lab module's PMA-2 docking port.

Illustration of Discovery on the V-bar, ready for final approach. Photo: Spaceflight Now/NASA TV

"They 'll translate right down the V-bar from in front of the station," Shannon said. "Jim Wetherbee will keep it within a pretty tight corridor.

To prevent hitting the station's delicate solar arrays with the exhaust plumes from the shuttle's braking rockets, Wetherbee will use so-called "low-Z" thrusters that are canted more toward Earth and deep space than the station. A small component of the thrust from the low-Z jets will act to slow the shuttle down.

On R-bar approaches from directly below, shuttle pilots enjoy natural braking from Earth's gravity and orbital mechanics. Wetherbee, on the other hand, will have to fire braking pulses as he approaches the station.

"The way you do that is you control your approach," Shannon said. "You'll see we don't stop at 170 feet when we're on the V-bar, we'll stop at 30 feet out. Jim will take a real good look ... to make sure he's exactly lined up.

"And then from 30 feet in," he said, "we really don't like to do braking pulses because they can plume the station."