This story was updated at 7:28 p.m.
EST.
WASHINGTON - Iridium Satellite LLC
confirmed today that one of its satellites was destroyed Tuesday in an
unprecedented collision with a spent Russian satellite and that the incident
could result in limited disruptions of service.
According to an e-mail alert issued
by NASA today, Russia's Cosmos 2251 satellite slammed into the Iridium craft at
11:55 a.m. EST (0455 GMT) over Siberia at an altitude of 490 miles (790 km).
The incident was observed by the U.S. Defense Department's Space Surveillance
Network, which later was tracking two large clouds
of debris.
"This is the first time we've ever
had two intact spacecraft accidentally run into each other," said Nicholas Johnson,
chief scientist of NASA's Orbital Debris Program Office at the Johnson Space
Center in Houston. "It was a bad day for both of them."
The collision appears to be the
worst space debris event since China intentionally destroyed one of its
aging weather satellites during a 2007
anti-satellite test, Johnson told SPACE.com. That 2007 event has
since left about 2,500 pieces of debris in Earth orbit, but more time is needed
to pin down the extent of Tuesday's satellite collision, he added.
"We're tracking more than 500 pieces
of debris which pose an additional risk to satellites," said U.S. Navy Lt.
Charlie Drey, a spokesperson for the U.S. Strategic Command which oversees the
U.S. Space Surveillance Network.
In a prepared statement, the
Bethesda, Md.-based Iridium characterized the incident
as a "very low probability event" and said it was taking immediate action to
minimize any loss of service. Iridium, which operates a constellation of 66 low
Earth orbiting satellites providing mobile voice and data communications
globally, said its system remains healthy and that it would implement a
"network solution" by Friday.
"Within the next 30 days, Iridium
expects to move one of its in-orbit spare satellites into the network
constellation to permanently replace the lost satellite," the statement said.
The 1,234-pound (560-kg) Iridium 33
satellite involved in the collision was launched in 1997; the 1,984-pound
(900-kg) Russian satellite was
launched in 1993 and presumed non-operational. It did not have a maneuvering
system, NASA said.
Iridium's spacecraft circle the
Earth along a near-polar orbit once every 100 minutes and fly at a speed of
about 16,832 mph (27,088 kph), the company states on
its Web site.
An unprecedented crash
Johnson said outdated spacecraft,
rocket stages and other components break
apart in space every year, but there have only been three relatively minor
collisions between such objects in the last 20 years. Never before have two
intact satellites crashed into one another by accident, he added.
The debris created in Tuesday's
collision is being tracked to assess its risk of damaging other satellites and
the International Space Station, which is currently home to two
American astronauts and one Russian cosmonaut.
The space station flies at an
altitude of about 220 miles (354 km), well below the impact point between the
Russian and U.S. satellites 490 miles (790 km) up. Johnson said that only a
very minor portion of debris from the two clouds is expected to descend across
the space station's orbital path.
"We believe that the increased risk
above the normal every day background risk is very, very small," Johnson said
NASA's orbital debris experts are
also assessing the threat to other spacecraft. The agency's Earth Observing
System satellites, which orbit at 438 miles (705 km), "are of highest interest
for immediate consideration," NASA said in its e-mail alert, a copy of which
was forwarded to Space News, a sister publication to SPACE.com.
Drey told SPACE.com that the
first hint of the collision came when Iridium officials contacted a U.S.
Strategic Command support office to report that they had lost contact with one
of their satellites.
"Shortly after, our space
surveillance center reported that they had observed multiple new objects in low
orbit," Drey said. The U.S. Space Surveillance Network continuously tracks more
than 18,000 separate man-made objects and debris at any given time, he added.
Tuesday's collision is the latest in
a series of satellite woes in recent weeks.
Last month, the nascent Eutelsat W2M
telecommunications satellite failed in
orbit just five weeks after it launched into space. Another communications
satellite, ASTRA 5A owned by SES Luxemburg, also failed and was adrift in
orbit. The loss forced its operators to warn the owners of neighboring
satellites to be prepared for the remote possibility of having to maneuver
their spacecraft to avoid a collision with Astra 5A.
NASA's Orbital Debris Program Office
also released an update last month on Russia's Soviet-era
satellite Cosmos 1818 stating that the spacecraft appeared to spew a cloud
of debris on July 4, 2008 that may be the result of leaking reactor coolant
from a debris strike or fragmentation.
SPACE.com Senior Editor Tariq
Malik contributed to this story from New York City.
