A Russian Soyuz spacecraft has lifted off from Kazakhstan with a U.S. Russian replacement crew for the International Space Station. It was the first human launch since the loss of the U.S. shuttle Columbia and its crew nearly three months ago.

Russian and U.S. flags flew at the launch pad as cosmonaut Yuri Malenchenko and astronaut Ed Lu took off from the Baikonur Cosmodrome in the remote Central Asian steppes. The pair is beginning a mission that will keep them at the station until October.

Mr. Lu's sleeve is adorned with a Columbia patch in honor his fallen shuttle colleagues. With shuttles grounded because of the February accident, the U.S. space agency NASA is relying for the first time on Russian craft to exchange and supply station crews. This means one less crewmember on the outpost until shuttles can fly again because the Russian vehicles cannot carry enough cargo for three.

This restriction forced NASA to drop a second Russian cosmonaut from this mission. As a result, Ed Lu is the first U.S. astronaut acting as Soyuz flight engineer. "Here I am trying to do something that no American has ever done before. What will be different is the fact that I'll be riding as the left-seater, that is, the board engineer or the co-pilot," he said. "That means a whole lot more than riding in the right seat, which is essentially the passenger seat."

NASA officials were on hand to witness the Soyuz launch after conferring with their Russian counterparts on the mission. Among them was space station flight director Joel Montelbano. He told reporters afterwards that the Soyuz launch is a tribute to the robustness of the 16 nation space station partnership. "The significance of today is we're continuing manned operations after a tragic accident with the shuttle program," he said. "While we study what happened with the shuttle, why it happened and correct that, it's very important to continue flying the space station."

Mr. Montelbano said the research outpost will operate safely with just two crewmen instead of three.

The work plans for astronaut Lu and cosmonaut Malenchenko changed radically after the Columbia disaster. Originally, three shuttles were to visit the outpost during their stay, bringing crews and hardware to continue its construction. The pair was to keep busy conducting maintenance spacewalks between shuttle dockings and performing many science experiments.

But because of the supply shortage, they will have no visitors and will do little science. Essentially, they will be caretakers for the station. But Mr. Lu said they will not be bored. "I actually think that this increment has the potential to be much more challenging than the original version of this increment simply because of the fact that we don't know what we're going to be doing. There are many more unknowns now and that is part of the fun of it," he said.

The Soyuz will dock with the space station on Monday after a two-day orbital chase. The new station residents will spend six days with the current crewmen, who will return to Earth one week later.