Crew members of the space shuttle Columbia, which returned to Earth early last month after a successful mission, said Monday the extraordinary challenge of working in space fostered a sense of unity that overrode differences in culture.Eight members of NASA's space team -- six aboard the spacecraft and two others who supported their operations from Earth -- were currently in Tokyo on a courtesy visit to Japan. "We are very pleased and proud to be here, representing the STS-87 (Space Transportation System 87)," commander Kevin R. Kregel told a news conference.The space shuttle Columbia returned to Earth on Dec. 5, after winding up 16 days of scientific research in outer space. During the operations, astronaut Takao Doi, 43, became the first Japanese to perform a spacewalk. He was accompanied by fellow mission specialist Winston Scott, 47, of the United States.Doi participated in two spacewalks during a mission to retrieve a malfunctioning satellite released from the shuttle to study the sun. "Although there is no gravity in space, the mass of an object doesn't change," Doi said, explaining the difficulties in handling the 1.5-ton satellite in space. "It was like I was trying to stop a car crawling toward me."Meanwhile, the eight astronauts, who hail from countries including the U.S., Ukraine, India and Japan, expressed belief that they shared a sense of unity during their 16-day mission. "It's always amazing to me how people can put their differences aside when they face a common challenge," Scott said. "When I first met Takao (Doi), it was 'Dr. Doi from Japan.' But after working together in space, I didn't see 'Takao from Japan' -- he was just 'Takao.'"