By Xinhua writer Mao Lei

    SAN FRANCISCO, Feb. 11 (Xinhua) -- The collision between U.S. and Russian satellites, the first "car crash" in outer space, highlights an urgent need to better manage increasingly dense space traffic, analysts say.

    A commercial satellite owned by Iridium Satellite LLC, collided with a defunct Russian military satellite at nearly 790 km over Siberia on Tuesday. The collision spewed out a pair of massive debris clouds that pose possible risks to other spacecraft.

    MORE DEBRIS TO EMERGE

    It has been documented that the collision already caused 600 pieces of debris, said Dr. William Marshall, an expert on small spacecraft at U.S. space agency NASA's Ames Research Center in California.

    "We don't know whether that's the final number yet. It always takes a few days for the U.S.-based surveillance network to track all of the pieces of debris. But certainly there is a possibility that more debris will emerge." Marshall told Xinhua in a telephone interview Thursday.

    "In a few days we'll find out for sure," said Marshall, who is also an advisor to the SpaceSecurity.org project.

    Marshall said there have been three previous cases in which satellites hit debris. One was a definitive case in which a French satellite, Cerise, hit a piece of debris, leaving the spacecraft severely damaged. There were other two cases in which Russian satellites seemed to have been hit by pieces of debris.

    Tuesday's crash, however, marked the first time a satellite hit another spacecraft, Marshall said.

    "That makes us very worried because the new debris created increases the probability of more events like this," he said. "Potentially, one could have a run-away effect."

    LACK OF TRAFFIC RULES

    Marshall believed the latest crash was most likely a random collision.

    "There is no data to date indicating that it was intentional on either party. Therefore no one was at fault," he said

    However, the accident exposed the lack of an established system to prevent such collisions.

    Marshall took the car as an example. "The current situation in space is a bit like being on the roads with not so many cars. We haven't yet decided whether we're going to drive on the left or the right side of the road."

    It was after two cars crashed that people began to realize that maybe they need to drive on a fixed direction, Marshall said.

    "Space is very big, but we have now put lots of satellites up there, and created lots of space debris, in particular by Russia and U.S. during the Space Age," he said. "Now it has started to become a problem."

    According to a report by The Wall Street Journal, more than 220active commercial satellites now orbit the globe, in addition to hundreds of military, spy and scientific satellites.

    At the beginning of this year, there were roughly 17,000 pieces of man-made debris orbiting the Earth, said Nicholas Johnson, chief scientist of NASA's Orbital Debris Program Office at the Johnson Space Center in Houston.

    Last April, scientists at the American Physical Society conference in Los Angeles said there were already more than 150 million pieces of debris, among which a large amount was junk created by astronauts.

    They predicted that the amount would still increase in the next200 years.

    Early statistics showed that about 45 percent of space debris was produced by the United States and 48 percent by Russia or former Soviet Union. China produced only 1.2 percent.

    Marshall pointed out that there have been no existing space traffic management rules so far and no measures have been taken to avoid collisions between satellites.

    He said there are orbital slots in geostationary orbit, while in low earth orbit, particularly in sun-synchronous orbits, there are no slots but close conjunctions of different satellites.

    "A lot of satellites pass over the poles: it's a more dense region and you'll notice that these two satellites hit close to the poles," he said.

    He called for need to think about how to do collision avoidance, "particularly above the poles in lower orbit in between 800 and 1,100 kilometers altitude."

    IDEAS FOR BETTER MANAGEMENT

    Marshall said the general debris problem is "becoming more acute," and many space scientists "are rethinking the need for space traffic management or collision avoidance between satellites."

    Tuesday's crash pointed out the need for nations to sit together to talk about space rules and treaties, he said. "I think that should happen as soon as possible."

    The expert said what the countries really need is a treaty to prevent major events like the latest collision, and help ensure that the space environment not get rapidly worse.

    "In addition, we need space traffic management, in particular generalized satellite conjunction analysis so that satellite operators can be warned of potential collisions in advance and maneuver out of the way."

    The expert also suggested the establishment of orbital slots and lanes in low earth orbit, as has already been done in geostationary orbit.

    Li Chien-Peng, a senior engineer with the Engineering Directorate of NASA's Johnson Space Center, told Xinhua that scientists now may have to consider designing "smarter" satellites to prevent such accidents.

    One option could be equipping satellites with a warning-system which can help them sense danger in advance and change orbit automatically to avert a collision.

    However, Li called the warning system-equipped satellite "only an assumption." "To make such satellites a reality, scientists should figure out a way to increase satellites' power supply as maintaining a stand-by warning-system needs a great amount of batteries."

    Scientists also have other options, including enlarging the fuel tanks on satellites, thus giving satellites extra time for self-destruction, Li said.