Russia's
Space Forces minimized the risk posed by a long-retired nuclear-powered
satellite that the U.S. Space Surveillance Network (SSN) identified as
producing "an unexpected debris cloud" in July.
In
statements released Jan. 21, the Space Forces said the Cosmos 1818 satellite,
orbiting at 800 kilometers, is not a danger
to other satellites in that orbit and will disintegrate when it reenters
the Earth's atmosphere sometime in the middle of this century.
A NASA
analysis of SSN data found that Cosmos 1818, launched in February 1987, was the
source of a "fragmentation event" around July 4 that released at
least 30
small pieces of debris.
In its
Orbital Debris Quarterly News report issued Jan. 15, NASA's Orbital Debris
Program Office says the debris could be droplets of sodium-potassium, which was
used as a coolant for the satellite's nuclear power generator. Direct exposure
to the sun could have warmed the coolant to a liquid state. NASA said the
released objects resemble
metallic spheres.
A satellite
featuring a similar design, called Cosmos 1867, has not released any similar
debris up to now, NASA said.
The NASA
analysis said Cosmos 1818 and 1867 were test satellites to demonstrate a new
kind of nuclear power in low Earth orbit, but at an altitude much higher than
the 250-kilometer operating orbit of Russia's Rorsat ocean-reconnaissance
satellites. A Rorsat satellite failed in orbit in 1978, breaking up in the
atmosphere and causing
radioactive debris to fall over Canada.
The NASA
report said that two years after China used a ground-based missile to destroy
the retired Chinese Fengyun-1C weather satellite in an 800-kilometer orbit, SSN
is tracking nearly 2,800 pieces of debris measuring at least 5 centimeters in
diameter. "The estimated population of debris larger than 1 centimeter is
greater than 150,000," NASA said. "The Fengyun-1C debris cloud easily
constitutes the largest
collection of fragments in Earth orbit."
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