WASHINGTON -- NASA Administrator Mike Griffin ruled out Chinese participation in the assembly of the International Space Station, adding that any U.S.-Chinese collaboration on human space flight projects would have to happen "well down the road." But Griffin also raised the possibility of nearer-term cooperation with China on Earth science and other unmanned space endeavors.

Speaking to reporters Sept. 25 in Beijing on the second day of a planned five-day visit to meet with Chinese space officials and get a first hand look at the Asian nation's growing space program, Griffin described the historic trip as a "get-acquainted visit."

Griffin is the first NASA administrator to make an official visit to China. He was invited to visit by Chinese President Hu Jintao during an April summit with U.S. President George W. Bush, who accepted on Griffin's behalf.

Griffin said during the press conference that NASA remains unable to cooperate with China's military-based space program due to U.S. proliferation concerns, but would continue to talk with the civilian side of China's space program to explore opportunities for cooperation.

He said the trip had already yielded an agreement with his Chinese counterpart, China National Space Administration Director Sun Laiyan, for NASA and CNSA to talk at least once a year and to explore establishing working groups in a number of areas, including Earth science, climate research, robotic missions and sharing data from various science missions. "We believe that might be a productive thing to do, and we are going to explore it," Griffin said.

Griffin, however, made clear that extending an invitation to China to join the international space station program was not in the cards.

"There are no plans on our part to work with China on the ISS construction," Griffin said in response to a question from a reporter. "The ISS program is the International Space Station program. In its present form, it is now approaching 13 years old. The partnerships that led to the development of the ISS are well established. I do not propose to change any of those arrangements at the present time."

Griffin did not rule out eventual cooperation with China "in the arena of manned space flight" but said that any such joint endeavors would happen after the United States and its partners complete development of the ISS.