A suit malfunction during a riskier-than-usual spacewalk forced the two crew members of the international space station (search) to go back inside early, leaving half their work undone.

Russian cosmonaut Alexander Kaleri (search) managed to return to the safe confines of the space station Thursday night, despite a spacesuit that was warm and damp.

Kaleri and American astronaut Michael Foale (search) had left the station empty when they ventured out, the first time the 5-year-old outpost had ever been unattended during a spacewalk. It was necessitated by the grounding of NASA's shuttle fleet in the wake of the Columbia accident.

Everything went well until three hours into the spacewalk, when Kaleri reported that the inside of his helmet was wet. Flight controllers immediately suspected a breakdown of the device that is supposed to regulate temperature and remove condensation.

"It's strangely warm," Kaleri said. A few minutes later, he radioed: "It's amazing. I have rain inside the helmet. I have water on the visor."

Russian space officials decided to cut the spacewalk short and advised Kaleri not to exert himself. Foale continued working as Kaleri rested. The cosmonaut said he could see well through the visor, even though it had a water film.

"I'm not moving too fast so I don't overheat," Kaleri said as he made his way to the hatch. Foale joined him in the air lock, and they closed the hatch.

The men, both veteran spacewalkers, managed to install some scientific experiments outside before Kaleri's suit began malfunctioning. The spacewalk was supposed to go 51/2 hours; it lasted three hours and 55 minutes.

The crewmen quickly discovered that one of the tubes through which water flows to cool Kaleri's suit, in the stomach area, was bent. Kaleri straightened the tube and water began flowing through it. He said he had no idea how the tube became bent.

Two spare Russian spacesuits are aboard that Kaleri could use if he and Foale have to go out again. However, no more spacewalks are scheduled for the rest of their six-month mission, due to end in April.

Throughout the spacewalk, flight controllers in Houston and Moscow watched over all the systems orbiting 230 miles up and were prepared, after months of safety analyses, to call the crewmen back in if a fire, decompression or some other emergency arose. What ended up happening — a suit malfunction — was not nearly as critical but still worrisome, especially with no one inside to help.

Normally, a third crew member stays inside during a spacewalk to oversee the systems, watch over the two outside and assist them when they re-enter. But the space station has been limited to a two-man crew since last spring to conserve supplies while the shuttle is grounded.

Before the spacesuit malfunction, Foale and Kaleri installed fresh trays of scientific samples to replace ones that had been hanging outside for more than two years to gauge the effects of space debris and other cosmic wear and tear. They also put out a radiation-measuring doll made of soft material to simulate human tissue, and photographed the area where they heard a strange metallic noise last November, to see if space junk caused any damage.

But they did not have time to replace a thruster contamination-measuring kit or relocate navigational reflectors for a new unmanned cargo ship due to arrive next year. Those chores will be left to the next crew, which is expected to conduct two spacewalks.

In its latest review of space station safety in light of the Columbia disaster, NASA acknowledged it needs to improve external surveys of the station and has set up a team to collect and review images. The revised 172-page report, released Friday, called the current surveying inadequate.

Space station cameras can check "a significant portion" of the exterior, but only spacewalkers or approaching spacecraft can see the so-called blind spots, the report stated. Until their grounding, shuttles had taken extensive photographs of the station during approaches and departures.

Extra video cameras will be installed on some future station parts, and an infrared camera is being developed to check for leaks and thermal degradation, the report said.