[meteorite-list] After Space Junk Goes Up, It Must Come Down

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun Jun 4 22:24:29 2006
Message-ID: <200606050156.SAA04311_at_zagami.jpl.nasa.gov>

http://www.sitnews.us/0606news/060406/060406_ak_science.html

After space junk goes up, it must come down
By Ned Rozell
SitNews (Alaska)
June 4, 2006

One winter night not too long ago, an Interior musher saw a fireball
blazing through the sky "like a flaming Nolan Ryan fastball."

As a baseball fan, I liked his comparison. But that can't be the
explanation for the blue flash that lit up the sky. Nolan Ryan retired
years ago.

To track down the real cause of the burst of light and the accompanying
boom, Fairbanks Daily News-Miner writer Mary Beth Smetzer called the
U.S. Space Command at Peterson Air Force Base, Colo. A staffer told her
the light show was not the result of anything manmade.

Other space-watchers told her a meteorite probably lit up the sky when
it entered Earth's atmosphere and glowed from the sudden friction of air
molecules. The meteorite, a fragment of some heavenly body, probably
caused a sonic boom as it whistled toward interior Alaska faster than
the speed of sound.

That's a good explanation, but I wondered how the people at U.S. Space
Command could be so sure our celestial visitor wasn't a piece of old
rocket or satellite sucked in by Earth's gravity. Space is crowded with
working and non-working satellites, rocket stages containing empty fuel
tanks and electrical controls, and other such rubbish. Do the sky
watchers at Space Command keep track of it all?

Yes.

"We have a handle on everything (in space) that's manmade," said Lt.
Col. Don Planalp, a spokesman for the U.S. Space Command. "We're
tracking about 8,000 different objects that are four inches (in
diameter) or bigger."

Space Command knows when a large rocket is launched from anywhere on
Earth. Heat-detecting satellites pick up the infrared waves emitted by
booster rockets during a launch. Once an object is in orbit, Space
Command tracks it with ground-based radar and cameras.

Whatever man lobs into Earth's orbit will someday come down, Planalp
said. Of the thousands of satellites blasted into space since the
Russians launched Sputnik in 1957, all will eventually return to Earth.

The closer an object circles Earth, the sooner its orbit will meet the
atmosphere, a 30-mile thick shell of gases covering the planet. Weather
satellites orbit about 300 miles above Earth. Geosynchronous satellites,
which carry many of our phone and television signals, are stationed
about 22,240 miles away.

Geosynchronous satellites "might be up there for millions of years,"
Planalp said. Other spacecraft, such as the one used for the Mars
Pathfinder Mission, will never return to Earth because they've been
blasted beyond Earth's gravitational pull.

Space Command scientists have calculated the orbits of all 8,000 pieces
of hardware zooming around the Earth, Planalp said. Though Space Command
scientists can pinpoint where manmade space debris will collide with
Earth's atmosphere, Planalp said there is no way to predict whether the
junk will skip off the atmosphere like a flat stone on water or whether
it will plunge to Earth.

If space junk does reach Earth's surface, it probably won't hit your
head, your house or your horse.

"There's not much danger," Planalp said. "Seventy-five percent of the
earth is water, and much of the remaining 25 percent is uninhabited. The
chance of being hurt or of property damage is infinitesimal."

Space Command knows of all the manmade stuff orbiting above us, but the
agency doesn't track meteorites, which typically arrive from deep space
without pausing to orbit Earth. Along with the aurora, unpredictable
meteorites are another good reason to look up when carrying a load of
groceries inside on an Alaska winter night. You never know when we'll be
treated to another flaming fastball in the sky.
Received on Sun 04 Jun 2006 09:54:55 PM PDT