MOSCOW -- The collision between U.S. and Russian communication satellites this week — the first such crash in space — has created speeding clouds of debris that threaten other unmanned spacecraft in nearby orbits, Russian officials and experts said Thursday.
The smashup 500 miles (800 kilometers) over Siberia on Tuesday involved a derelict Russian spacecraft designed for military communications and a working U.S. Iridium satellite, which serves commercial customers as well as the U.S. Department of Defense.
In a statement Thursday, Iridium, based in Bethesda, Maryland, denied that it was responsible for the crash. The collision scattered space debris in orbits 300 to 800 miles (500 to 1,300 kilometers) above Earth, according to Maj.-Gen. Alexander Yakushin, chief of staff for the Russian military's Space Forces.
But Igor Lisov, a prominent Russian space expert, said Thursday he did not understand why NASA's debris experts and Iridium had failed to prevent the collision, since the Iridium satellite was active and its orbit could be adjusted.
"It could have been a computer failure or a human error," he said. "It also could be that they only were paying attention to smaller debris and ignoring the defunct satellites."
Lisov said the debris may threaten a large number of earth-tracking and weather satellites in similar orbits.
"There is a quite a lot of satellites in nearby orbits," he told The Associated Press. "The other 65 Iridium satellites in similar orbits will face the most serious risk, and there numerous earth-tracking and weather satellites in nearby orbits. Fragments may trigger a chain of collisions."
Both the U.S. Space Surveillance Network and Russian Space Forces are tracking the debris, believed to be traveling at speeds of around 200 meters — or about 660 feet — per second.
NASA said it would take weeks to know the full magnitude of the crash, but both NASA and Russia's Roscosmos agencies said there was little risk to the international space station and its three crewmembers.
"There is no immediate danger, but we will carefully monitor the situation," Russian Mission Control spokesman Valery Lyndin told the AP. He noted the station's orbit has been adjusted in the past to dodge space debris.
The space junk also poses no threat to the space shuttle set to launch Feb. 22 with seven astronauts, U.S. officials said, though that issue will be reviewed.
The Iridium orbiter weighed 1,235 pounds (560 kilograms), he said, and the decommissioned Kosmos-2251 military communications craft weighed nearly a ton. The Kosmos was launched in 1993 and went out of service two years later in 1995, Yakushin said.
Some Soviet-built, nuclear-powered satellites long out of action in higher orbits may also be vulnerable to collisions, Lisov said. If one of them collides with the debris, the radioactive fallout would pose no threat to Earth, Lisov said, but its speeding wreckage could multiply the hazard to other satellites.
Nicholas Johnson, an orbital debris expert at the Houston space center, said the speeding junk could reach the orbit of the Hubble Space Telescope.
Iridium said the loss of the satellite was causing brief, occasional outages in its service and it expected to fix the problem by Friday. The company said it expected to replace the lost satellite with one of its eight in-orbit spares within 30 days.
"The Iridium constellation is healthy, and this event is not the result of a failure on the part of Iridium or its technology," the statement said.
No one has any idea yet how many pieces of space junk were generated by the collision or how big they might be.
"Right now, they're definitely counting dozens," said Mark Matney, an orbital debris scientist at Johnson Space Center in Houston. "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.
This was the first high-speed impact between two intact spacecraft, NASA officials said.
There have been four other cases in which space objects have collided accidentally in orbit, NASA said. But those were considered minor and involved parts of spent rockets or small satellites.
At the beginning of this year, there were roughly 17,000 pieces of manmade debris orbiting Earth, according to NASA. The items, at least 4 inches (10 centimeters) in size, are being tracked by the U.S. Space Surveillance Network, which is operated by the military.
Orbital debris is now the biggest threat to a space shuttle in flight, surpassing the dangers of liftoff and return to Earth.
The Iridium satellite network, initially launched by Motorola Inc. in the 1990s, plunged into bankruptcy in 1999. Private investors relaunched service in 2001.
Iridium satellites are unusual because their orbit is so low and they move so fast. Most communications satellites are in much higher orbits and don't move relative to each other, which means collisions are rare.