HOUSTON Space Shuttle Atlantis crew is set to enter the International Space Station (ISS) later tonight following a successful early morning spacewalk to work on the orbital outpost.

"This really sets the tone," said Mike Hess, the missions lead EVA (extravehicular activity) officer. "We have a surge of spacewalks about to occur over the next year and half or so, we have 20 spacewalks planned."

Hess said this particular spacewalk was one of the most challenging in his 11 years of planning them. Training was split between Russia and the United States because no one location housed all of the mock-ups needed for practice by the astronauts.

Todays spacewalk was sixth in a series of more than 160 needed to maintain and complete the station by sometime in 2006.

Following this mornings spacewalk, Atlantis fired its thrusters and boosted the station into a slightly higher orbit.

Ed Lu, followed by Yuri Malenchenko, exited the orbiters airlock at about 12:58 a.m. Eastern Daylight Time (04:58 GMT) to begin their slightly more than six hour odyssey to ascend almost 100 feet (30 meters) up the 143-foot (42.9-meter) -long space station.

After gathering their tools and equipment from a storage box in the orbiters payload bay, the duo rode the orbiters 50-foot (15-meter) robotic arm to their first work site on the station. Lu, who is making his first spacewalk, had only one comment about the station, "Its beautiful."

Riding alongside Lu was cosmonaut Malenchenko who spent about four months aboard the Russian space station Mir in 1994 and made two spacewalks totaling about 12 hours.

Rick Mastracchio, a former flight controller, operated the arm, which also has a camera mounted on it, while Dan Burbank, a U.S. Coast Guard lieutenant commander, orchestrated the spacewalkers efforts.

First order of business was a recently added task inspect a docking target aboard the Russian service module that failed to deploy. Though the target is no longer needed, it was in the path of the ascending astronauts and a potential hazard if it popped out. Lu swung the target out and they continued their journey along the station.

Both spacewalkers trained in the 40-foot (12-meter) deep pool at Johnson Space Centers Neutral Buoyancy Lab and in the Hyrdrolab in Star City near Moscow to prepare for their tasks.

"The mock-up in the Hydrolab looks a lot like the real one. My compliments to the builders," Lu said. "Its all very familiar."

Lu and Malenchenko climbed quickly to their next location to add a 6-foot (1.8-meter) boom to the magnetometer on the service module. The magnetometer determines the stations altitude and it was too close to the station to give accurate readings. Lu undid eight bolts on a cover and stowed them in a special pouch while Malenchenko assembled the boom and handed it to his colleague for installation.

Moving further up the station, both spacewalkers worked to install four video cables to be used with cameras for docking Russian Progress supply vehicles. Lu and Malenchenko attached the 16-foot (4.8-meter) long cables and secured them to the station with fasteners.

The pair moved swiftly to install a series of power cables to allow electricity to flow between the Russian modules and future U.S. modules. They finished out their tasks ahead of schedule by installing a 20-foot (6-meter) cable that connects into a Russian Orlan spacesuit to allow telemetry to be sent to the ground stations.

Later tonight, the crew enters the station for the first time to begin the almost five day process of transferring supplies and installing equipment in the station. Air filters and scrubbers aboard the three modules comprising the station have been operating since docking to clean the air before the crew enters.

ISS lead flight director Mark Ferring likened the stations atmosphere to the interior of a car on a hot day.

"Its like in your car when its hot in the summer and you open the door and can kinda smell some components of chemical-type smells that you dont notice normally, or its cool, or the windows are open," he said "The materials inside the spacecraft outgas some of their chemicals into the air."

Medical personnel have set certain air quality standards, he said, and the filters bring the air back into tolerances.

Atlantis will undock from the station late Saturday, though mission managers are likely to extend the mission another day to give the astronauts more time to work on the station. Currently, Atlantis is scheduled to land at Kennedy Space Center (KSC) early Tuesday morning.

As Lu and Malenchenko worked high above Earth, technicians at KSC began rolling Space Shuttle Discovery to the launch pad. The shuttle and its seven-person crew will lift off October 5 for final preparations to the station, for its first occupants scheduled to arrive in late October. During Discoverys mission, the crew will make four spacewalks primarily to install the Z-1 truss that contains gyroscopes and an antenna for the station.

The first space station crew consists of Commander Bill Shepherd and cosmonauts Yuri Gidzenko and Sergei Krikalev. The trio is scheduled to fly to the station aboard a Soyuz spacecraft launched from the Baikonur Cosmodrome in Kazakhstan.