WASHINGTON - The in-orbit collision
that destroyed an operational Iridium communications satellite over Siberia
last week underscores the difficulty of predicting and avoiding such events
despite the increasingly sophisticated orbital surveillance technology in use,
U.S. government and industry experts said.
According to some experts, this Feb.
10 incident, the first
known collision between two fully intact satellites - Iridium 33 and
Russia's spent Cosmos 2251 communications craft - is a sign of things to come
as the orbital environment gets more crowded.
"While it took 50 years for
Earth orbit to become
sufficiently congested that we would expect such an event, it will take
only about 10 years before another can be expected," said Don Kessler, an
orbital debris expert who previously worked for NASA.
"The probability of impact has
been steadily going up and at some periods at an increasing rate," said
John Higginbotham, chief executive of satellite control software provider
Integral Systems of Lanham, Md. "We're definitely in one of those periods
and I expect to see an increase in the coming years."
According to a Feb. 11 e-mail alert
issued by NASA, Russia's 1,984-pound (900-kg) Cosmos 2251 -launched in
1993 but out of service since 1995 - collided with the 1,234-pound
(560-kg) Iridium craft at 11:55 a.m. EST at an altitude of 490 miles (790 km).
Bethesda, Md.-based Iridium Satellite LLC alerted the U.S. Air Force after
losing contact with the Iridium 33.
Space traffic tracking
Although the Air Force operates a
space surveillance network that currently tracks some 19,000 orbital
objects, some as small as a baseball, the service cannot monitor all possible
collision scenarios, experts said. Bob Hall, technical director of Analytical
Graphics Inc. of Exton, Pa., said the Iridium
33-Cosmos 2251 collision was not even in the top 150 of potential close
calls being monitored by his company during the week.
"It wasn't even the closest of
all predicted Iridium conjunctions," Hall said, referring to close
approaches between satellites.
Nick Johnson, an orbital debris
expert with NASA's Johnson Space Center in Houston, said it is not the Air
Force's role to stay on top of every potential collision involving satellites
in Earth orbit. He said that with enough resources, it might be possible to
have such a capability, in which case Iridium's loss potentially could have
been avoided. But he added that it is impossible to predict with certainty
whether a collision between two space objects will occur and said there
frequently are near-misses involving the Iridium system, which consists of 66 operating satellites in low Earth orbit and eight in-orbit
spares.
"There's no such thing as space
traffic control and that's one of the problems," added Higginbotham.
According to Johnson, Cosmos 2251
drifted down from a higher orbit to the Iridium satellite's altitude.
In a written response to questions
Feb. 13, Iridium spokeswoman Liz DeCastro said
the company was not notified by the Air Force of the danger posed by Cosmos
2251, and did not attempt to maneuver its satellite out of danger. Industry
sources said that typically, satellite operators conduct their own analyses and
request information from the Air Force when it appears that a close approach,
or conjunction, involving one of their craft is likely.
In a statement issued to media Feb.
11, Iridium said it would move one of its in-orbit satellites within 30
days to permanently replace the lost satellite. The company announced Feb. 13
that it had completed a "service hole patch"
as a stopgap measure against limited services disruptions resulting from the
loss of the satellite.
Watching the wreckage
NASA and the Air Force are
monitoring the potential threat posed by the debris to any U.S. spacecraft, including the
International Space Station. Johnson characterized the risk to the space
station posed by the debris as "very, very low."
NASA's large Earth
observation satellites, which orbit at 705 kilometers, "are of
highest interest for
immediate consideration," NASA said in its notification about the
incident.
Two years ago, a group of commercial
satellite operators began exchanging information to help monitor the risks of
collision.
"As the fleets of the commercial
satellite operators have grown in size and complexity, operators have had to be
creative and resourceful in how they manage those fleets," said Richard DalBello, vice president of legal and government affairs at
Intelsat General, Bethesda. "The first thing the operators did was to
establish protocols for sharing data and communications between operators.
Recently, this has led to a proposal among the large operators to create a data
center where information could be exchanged rapidly ... in a common format."
An insurance industry source said
the collision could affect the way insurance policies are written and rates are
figured in the future. "Until a few days ago, this was seen by the
insurance industry as a non-issue. Now everyone's taking a hard look at
this," the source said.
Asked whether a given company's
process for monitoring potential threats factors into how insurance rates
are calculated, the source said, "We have not in the past but we will
be now."
Tariq Malik contributed to this
article from New York. Leonard David contributed to this article from Golden,
Colo.
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