The Future of Air Traffic Control

Hazardous Space Junk?

The official word is that the chances of human casualties as a result of orbiting or re-entering debris are small. But according to NASA itself, the growth in the amount of debris poses a "rapidly increasing hazard."

NASA's Space Science Branch at the Johnson Space Center believes that approximately one cataloged piece of debris has fallen to Earth every day for the last 40 years. Because most junk burns up as it re-enters the atmosphere and the sheer size of Earth's land mass, the risk that falling space debris poses to anyone is extremely small.

            However, according to my research, there are several reports of farm animals being injured and at least one fatality due to space junk.

            The U.S. Space Command tracks more than 8,000 orbiting objects larger than 4 in (10 cm), of which only 7% are operational. The rest are debris—dead satellites, parts of exploded rockets, nuts, bolts, other lost hardware, etc. Most orbital debris is found in Low Earth Orbit (LEO), in altitudes below 1,243 mi (2,000 km). At these altitudes, objects collide at a speed of 6.2 mi per second (10 km/sec). In such velocities, even very small objects can inflict serious damage. It is estimated that smaller, non-tracked debris number in the millions. How much damage can an object smaller than 4 inches inflict in space? NASA documented a cracked space shuttle window from an impact with a paint chip estimated to be 0.008 in (0.2 mm) in diameter. Larger debris could cause damage up to and including a complete breakup of the spacecraft.

            According to a NASA report, the chances of collision increase with the size of the object and the longer it stays in orbit.

The United States has taken an official stand that is outlined in the 1996 National Space Policy that clearly states: "The United States will seek to minimize the creation of new orbital debris."

The Air Force Space Command tracks debris larger than 4 inches and gives warning to NASA and others if trash is projected to come close to astronauts. Several times NASA has moved the space station to dodge nearby junk. But that's only the debris the Air Force can track.  "The greatest risk to space missions comes from the non-trackable debris," says Nicholas Johnson, chief scientist of NASA's Orbital Debris Program Office in Houston, Texas.

The most spectacular re-entry in the short history of the phenomenon was Skylab. Launched in 1973, the first and only U.S. space station made re-entry six years later, part of it splashing into the Indian Ocean and another portion ending up in Australia.

For more pictures of space junk in low earth orbit and high earth orbit, visit the photo album link on the right side of your screen. For more information about space junk visit http://www.nasa.gov

By: Amber Markham, Air Traffic Controller