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Beyond the Holographic Universe - 超越宇宙全息

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 NASA Forced to Steer Clear of Junk in Cluttered Space

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Join date : 2007-07-24
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PostSubject: NASA Forced to Steer Clear of Junk in Cluttered Space   NASA Forced to Steer Clear of Junk in Cluttered Space Icon_minitimeSat Aug 04, 2007 10:51 pm

Published: July 31, 2007

Traffic in space is getting so congested that flight controllers in the past few weeks have had to nudge three spacecraft out of harm’s way, in one case to prevent the craft from colliding with its own trash.
On July 23, controllers in Houston raised the orbit of the International Space Station by roughly five miles to avoid hitting a half-ton tank of ammonia that a spacewalking astronaut had tossed out earlier in the day while doing some housecleaning on the $100 billion outpost.

“We don’t normally dump something like this,” said Lynette Madison, a spokeswoman at the Johnson Space Center. But, she added, the space shuttle had no room in its schedule for returning the refrigerator-size tank to Earth. Officials expect the container to orbit the Earth for nearly a year before making a fiery re-entry.

Another episode took place on July 4, as the nation relaxed for the holiday. Ground controllers at Goddard Space Flight Center in Greenbelt, Md., fired up the engines on NASA’s CloudSat, a $217 million environmental satellite that peers inside cloud formations with a powerful radar, to dodge a mini satellite launched by Iran in 2005.

Cheryl L. Yuhas, head of earth science missions at the Washington headquarters of the National Aeronautics and Space Administration, said the maneuver put more than two miles between the two spacecraft, preventing a potential crackup.

Officials and private space experts say episodes like these illustrate the danger of a drastic rise in satellites and space debris in Earth’s orbit. Early this year, after decades of growth, the federal catalog of detectable objects (four inches wide or larger) orbiting Earth reached 10,000, including dead satellites, old rocket engines and junkyards of whirling debris left over from chance explosions and weapon tests.

Now, that number has jumped to 12,000. China’s test of an antisatellite weapon in January and four spacecraft breakups in February, one of them mysterious, have contributed to the buildup of debris. Space officials worry that a speeding bit of space junk could shatter an object into dozens or hundreds of fragments, starting a chain reaction of destruction.

Experts said that moving spacecraft out of the way to avoid collisions, once a rare way of dealing with potential threats, is becoming increasingly common.

On June 22, nearly two weeks before the CloudSat maneuver, ground controllers at Goddard nudged NASA’s Terra, an environmental satellite, out of harm’s way.

American space experts had calculated that debris from China’s antisatellite test might hit the $1.3 billion spacecraft, which can gauge environmental health by measuring changes in the greenness of the planet’s surface.

“It was a close call,” said Lauri Newman, a flight engineer at Goddard who assesses collision threats. “But we have a process in place that obviously worked.”

NASA officials said the debris came no closer than a half mile to the Terra.

The Chinese weapon test, on Jan. 11, shattered an aging weather satellite into hundreds of bits, in what space experts describe as the worst satellite fracture of the space age.

Soon after that, four more breakups added to the debris problem: On Feb. 2, a new Chinese navigation satellite suffered an apparent engine failure that left it in dozens and perhaps hundreds of pieces. On Feb. 14, an abandoned Russian engine broke into roughly 60 detectable pieces, apparently because residual fuel had exploded.

On Feb. 18, a retired spacecraft jointly developed by China and Brazil suddenly and mysteriously broke into dozens of pieces. American experts suspect it was the victim of a collision with other space debris.

Then on Feb. 19, a large Russian space tug exploded, apparently from residual fuel, creating a cloud of about 1,000 pieces of detectable debris.

Orbital Debris Quarterly News, a NASA publication, noted that at least three of the four breakups appeared to have been preventable if more caution had been exercised in designing and operating the vehicles.
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