Russian and U.S. experts say the first-ever collision between two satellites has created clouds of debris that could threaten other unmanned spacecraft.
Russia's Mission Control spokesman Valery Lyndin says there is little risk to the international space station with three crew members aboard.
Lyndin said Thursday that officials would monitor the debris from Tuesday's collision to make sure no fragments get near the station. He said the station's orbit was adjusted in the past to avoid debris.
Other Russian and U.S. officials warn that satellites in nearby orbits could be damaged.
The smashup occured over Siberia when a derelict Russian military communications satellite crossed paths with a U.S. Iridium satellite.
The two big communications satellites collided in the first-ever crash of two intact spacecraft in orbit, shooting out a pair of massive debris clouds and posing a slight risk to the international space station.
NASA said it will take weeks to determine the full magnitude of the crash, which occurred nearly 500 miles (800 kilometers) over Siberia on Tuesday.
“We knew this was going to happen eventually,” Mark Matney, an orbital debris scientist at Johnson Space Center in Houston, told The Associated Press.
NASA believes any risk to the space station and its three astronauts is low. It orbits about 270 miles (430 kilometers) below the collision course. There also should be no danger to the space shuttle set to launch with seven astronauts on Feb. 22 or later, officials said, but that will be re-evaluated in the coming days.
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 (560 kilograms), and the Russian craft nearly a ton.
Hundreds of pieces of debris
The U.S. Strategic Command's Space Surveillance Network detected the two debris clouds created by Tuesday's collision. Julie Ziegenhorn, a spokeswoman for the Strategic Command, told msnbc.com that the collision left behind an estimated 600 pieces of debris, but she emphasized that the Pentagon's orbital watchdog had to do "still more characterization" of the collision's potential effect.
NASA's Matney said the count would likely be in the thousands if pieces of debris down to the scale of microns — about the size of a grain of sand — are included.
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.
Nicholas Johnson, an orbital debris expert at the Houston space center, said the risk of damage from Tuesday’s collision is greater for the Hubble Space Telescope and Earth-observing satellites, which are in higher orbit and nearer the debris field.
At the beginning of this year there were roughly 17,000 pieces of manmade debris orbiting Earth, Johnson said. All those items, at least 4 inches (10 centimeters) in size, are being tracked by the Space Surveillance Network.
Litter in orbit has increased in recent years, in part because of the deliberate breakups of old satellites. It’s gotten so bad that orbital debris is now the biggest threat to a space shuttle in flight, surpassing the dangers of liftoff and return to Earth.
Ziegenhorn said the Strategic Command and NASA have been working together to make sure the space station and any shuttles in flight are kept a safe distance away from any encroaching objects. "Manned spaceflight needs are a priority," she said.
‘Minimal impact’ on Iridium service
Iridium Holdings LLC has a system of 65 active satellites which relay calls from portable phones that are about twice the size of a regular mobile phone. It has more than 300,000 subscribers. The U.S. Department of Defense is one of its largest customers.
In a statement, Iridium said the collision would have "minimal impact" on service.
"This satellite loss may result in very limited service disruption in the form of brief, occasional outages," the statement said. "Iridium expects to implement a network solution by Friday."
Company spokeswoman Liz DeCastro told msnbc.com that the interim solution would involve shifting resources to cover affected areas. Within 30 days, Iridium plans to move one of its in-orbit spares into the telecommunications constellation to replace the lost satellite.
Initially launched by Motorola Inc. in the 1990s, Iridium 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.
Iridium Holdings LLC is a privately held company that recently announced a merger deal with New York-based investment firm Greenhill & Co. through a subsidiary, GHL Acquisition Corp. The merger is due to be completed in the next few months.
This report includes information from The Associated Press and msnbc.com. An earlier version of this report mischaracterized the status of the merger involving Iridium and GHL Acquisition Corp. Registered users may obtain detailed data about orbital debris by checking the Space-Track Web site.