What Is Space Debris?

The problem of space debris in orbit around the Earth has been getting worse since the earliest days of the space program. Space debris is made up of anything and everything from old satellites that either malfunctioned or have exhausted their usefulness to hand tools that may have been dropped by NASA or Russian spacewalk crews. Almost anything no longer serving a useful purpose and orbiting the Earth without the power to alter its course could be considered space junk.

Space Junk Means Space Bullets

The term space junk may seem innocuous enough, but, in reality, each bit of space junk might be more accurately called a space bullet. These space bullets fly around and around the Earth at speeds ranging from 6,500 miles per hour to over 17,000 miles per hour. Compare that to actual bullets that generally travel at less than 700 miles per hour.

U.S. Space Surveillance Network

According to NASA , there are over 19,000 manmade objects bigger than 10 centimeters in diameter whizzing around and around the Earth at various heights. Objects of this size are tracked by the U.S. Space Surveillance Network so that things like Space Shuttles can maneuver out of the way should a piece of space debris be headed toward them. You can see a graphical representation of all orbiting manmade objects larger than 10 cm in diameter here.

Too Much Space Junk to Count

In addition to the 19,000 tracked large objects, NASA estimates that there are half a million bits of space junk between 1 and 10 centimeters in size also orbiting the Earth. Once we start talking about objects smaller than 1 centimeter in diameter, the number jumps to tens of millions.

The Danger of Space Debris

The danger posed by space debris is more than just theoretical. In 2009, an active U.S. Iridium satellite was hit and completely destroyed by an old Russian Cosmos satellite that was no longer in operation. Of course, this high speed collision shattered both satellites creating thousands more smaller bit of space debris.

Decaying Orbits

Most space debris rings the Earth in decaying orbits. A decaying orbit is one in which the object gradually loses altitude as it circles the globe. Depending upon the height of the object's orbit, it can last for as little as a few years to more than 100 years. Eventually, objects with decaying orbits will re-enter the Earth's atmosphere. Once an orbiting object enters the atmosphere friction slows it even more quickly.

Space Junk Risk to Objects on Earth

These objects will either burn up from the heat of this atmospheric friction or it will fall to the Earth. NASA says that an average of one piece of catalogued space debris falls back to Earth each day. Usually, these go unnoticed, either burning up or falling into the oceans or in unpopulated areas. The risk of any person or building on Earth being hit by a falling piece of manmade space debris is miniscule.

Space Debris Risk to ISS and Other Objects

Structures like the International Space Station (ISS) generally use shielding to protect critical areas from damage caused by the impact of small space debris. NASA says the ISS shielding can withstand impacts from space debris up to 1 centimeter in diameter. Other objects may have attitudinal rockets which allow them to maneuver in orbit. These smaller objects can usually move out of the path of any known approaching pieces of space debris, while their fuel lasts. Maneuverable vehicles like the space shuttle routinely dodge such space bullets if there's even a chance that the object will come close. Other satellites may not have the ability to maneuver and must simply take their chances.

Governments Acknowledge Growing Space Junk Risk

Most space-faring countries and the United Nations recognize the danger of space debris and have adopted policies that attempt to lower the rate of creation of new pieces of space debris. Any new man-made object that goes into orbit, however, will be accompanied by some bit of debris that increases the risk to existing satellites.

Although the vast majority of space debris is man-made, there is also some risk posed by natural meteors. Small bits of dist or rocks fly through the solar system by the billions. Although only a small portion intersect the Earth's orbit, it is possible, though relatively rare, for these small, naturally occurring objects to seriously damage satellites as well. The increasing use of Earth's orbital space for satellites and research stations like the ISS, mean that the amount of man-made space debris and the risk of colliding with it, will continue to increase over time.

End of Life Space Junk Mitigation Plans for Satellites

Cognizant of the risk to their own future satellites, many communications companies with satellites in orbit, plan for the end of life of their satellites. As a satellite approaches the end of its usefulness, some companies will activate onboard maneuvering systems to nudge the satellite out of its old orbit into a higher one. These higher orbits help get the old satellite out of the area used by most active satellites and mean that it will take decades longer for the defunct satellite to fall to Earth. While this is helpful, even these modified orbits will eventually decay dropping these old satellites back into lower orbits and eventually into the Earth's atmosphere.

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