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More Satellite Collisions Could Occur, Experts Say

BY Admin  February 12, 2009 at 2:35 PM EST

Satellite; Photo courtesy Iridium Satellite LLC

Tuesday’s unprecedented
crash involved a privately owned U.S. communications satellite and a
defunct Russian military satellite.

While the hundreds of
new speeding bits of space junk could threaten the manned International Space
Station and other satellites, the geopolitical fallout could be even greater,
according to some experts.

“This is an event
that really makes us realize that things are not so straightforward as we
originally thought,” Francisco Diego, a senior research fellow in physics
and astronomy at University College London, told Reuters. “I couldn’t put
a number on the probability of this happening again, but now that it has
happened, it changes things a lot and it becomes a concern.”

In a statement
Thursday, Bethesda, Md.-based communications group Iridium denied that it was
responsible for the crash over Siberia. The
collision scattered space debris in orbits 300 to 800 miles above Earth,
according to Maj. Gen. Alexander Yakushin, chief of staff for the Russian
military’s Space Forces.

Iridium said it planned
to move one of its in-orbit spare satellites into the constellation to replace
the lost craft within 30 days.

The collision occurred
at roughly 485 miles above the planet, an altitude used by satellites that
monitor weather and carry telephone communications among other things, Air
Force Col. Les Kodlick of the U.S. Strategic Command said. The International
Space Station flies at a lower altitude and is the command’s top priority in
attempting to prevent collisions.

“If you want a global
coverage with high resolution, this is where you go,” said Bo Andersen,
director general of the Norwegian Space Agency, referring to the altitude.

“If you go much
further down, you get more drag from the atmosphere which shortens the life of
the satellite; if you go higher up, the resolution gets worse,” he said.

The collision happened
not far from the orbit of a defunct weather satellite blown up by a
ground-based missile in a Chinese weapons test in 2007. European and U.S. officials
argue the resulting debris made it harder to identify crash risks.

Scientists say
predicting collisions is difficult because of the unpredictable behavior of
other objects, solar radiation and the gravitational effect of the moon and Earth,
while molecular wisps of atmosphere can gently skew orbits.

“You can calculate
potential collisions some time in advance but orbits change, especially when
you have a defunct satellite which you cannot correct,” Andersen said.

The Russian satellite
lacked a propulsion system and could not have been nudged out of the way. It
was not immediately clear if Iridium, which owned the U.S. satellite,
tried to avoid the collision or had an early warning about what space officials
call a “close conjunction.”

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, according to the
Associated Press. “It also could be that they only were paying attention
to smaller debris and ignoring the defunct satellites.”

Both the U.S. Space
Surveillance Network and Russian Space Forces are tracking the debris, believed
to be traveling at speeds of around 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 crew members. Russian Mission Control spokesman Valery
Lyndin noted the station’s orbit has been adjusted in the past to dodge space
debris.

Among the 18,000-plus
objects being tracked in space by the U.S. Strategic Command are operational
and defunct satellites, spent rocket boosters and debris that is 3.9 inches in
diameter or larger.

Nicholas Johnson, an
orbital expert at NASA’s Johnson Space Center
in Houston,
said it was uncertain how much new debris had been created by the crash.

“It takes a while
for the debris to spread out and for us to get an accurate head count,” he
said. NASA contracts with the Department of Defense for orbital tracking
services and regularly maneuvers its spacecraft to avoid any crashes.

U.S. officials said the space junk posed no threat to
the space shuttle set to launch Feb. 22 with seven astronauts, though they
planned to review the issue.

The Iridium orbiter
weighed 1,235 pounds 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.

European space
scientists said they were aware of the potential for a close encounter between
Russian and U.S.
satellites before they crashed, but the difficulty of predicting orbits and
“noise” from thousands of pieces of debris made a definitive
prediction of a collision impossible.

“The ‘catalog’ of
objects and debris showed a possible approach between the paths of the two
satellites but an approach doesn’t necessarily mean a collision, and you would
need more information to be certain,” Philippe Goudy, deputy director of
the French space operations control centre at Toulouse, told Reuters.

Some satellites fly
within a few hundred meters of each other every day, Johnson told Space.com.
Each year, there are about six instances in which old satellites and satellite
parts break apart in what scientists call “fragmentation events.”
Satellite components or spent rocket stages have accidentally collided three
times before in the last 20 years.

“This is the first
time we’ve had two intact spacecraft collide, so it is a big deal,” he
said. “But you know, it’s not unexpected.”