In a space first, two communications satellites collided and were destroyed yesterday about 500 miles above Russia, NASA reports.

Officials told Spaceflight Now that the International Space Station did not appear to be threatened by the giant debris cloud. It's not clear, however, if other military or civilian satellites may be at risk.

The collision involved an Iridium communications satellite, which was launched in 1997, and a Russian Cosmos satellite launched in 1993 that apparently was not functioning. Each weighed more than 1,000 pounds, and officials said they were tracking hundreds of pieces of wreckage produced by the crash.

The collision involved an Iridium commercial satellite, which was launched in 1997, and a Russian satellite launched in 1993 and believed to be nonfunctioning. The Russian satellite was out of control, Matney said.

The Iridium craft weighed 1,235 pounds, and the Russian craft nearly a ton.

No one has any idea yet how many pieces were generated or how big they might be.

"Right now, they're definitely counting dozens," Matney said. "I would suspect that they'll be counting hundreds when the counting is done."

As for pieces the size of micrometers, the count will likely be in the thousands, he added.

"There are two issues: the immediate threat and a longer-term threat," he said. "It turns out, when you have a collision like this the debris is thrown very energetically both to higher orbits and to lower orbits. So there are actually debris from this event which we believe are going through the space station's altitude already. Most of it is not, most of it is still clustered up where the event took place. But a small number are going through station's altitude.

"Yesterday, we did an assessment of what the risk might be to station and we found it's going to be very, very small. As time goes on, (that) debris will (come down) some over months, most over years and decades and as the big ones come down they'll be tracked, we'll see them and the worst-case scenario, we'll just dodge them if we have to. It's the small things you can't see are the ones that can do you harm."