What happens to orbiting satellites, spacecraft or other materials when they reach the end of their useful life? Sadly, they become space “junk” and may pose a serious hazard to other spacecraft for years, before eventually burning up in the atmosphere. As the use of space grows, so will this problem. What can be done to fix it?
For the past several years, about 80 rocket launches annually place an average of 300 metric tons, or 300,000 kilograms, of spacecraft into orbit around the Earth. As of 2008, there was more than 5,500 metric tons of orbiting space debris, with more accumulating each year. The problem is that the debris does not remain whole, but often fragments into tiny pieces due to accidental collision or deliberate destruction.
There are more than 20,000 objects larger than 10 centimeters in diameter, and over 100 million objects smaller than 1 centimeter. While NASA keeps track of more than 500,000 space objects, the U.S. Air Force actively tracks only 23,000 large objects (including debris) that pose the greatest threat to active spacecraft. To increase tracking capacity, the U.S. is developing a next-generation “space fence” that will track roughly 200,000 objects using high-resolution radar.
Solutions to deal with space debris
Because of their high speeds (several kilometers per second), even very small objects, such as paint flecks can damage or disable operational spacecraft. Currently, the main strategy for dealing with space debris is to avoid it. Tracking systems issue warnings when debris is likely to venture too close to operational spacecraft, which – with enough forewarning – can change their orbits slightly to avoid collision, a process known as “debris avoidance maneuvers.”
For human-occupied spacecraft such as the International Space Station, people can retreat to safer parts of the station, or, if necessary, evacuate entirely. For debris too small to track, spacecraft are designed to withstand impacts via protective outer layers, but it is no guarantee.
One of the greatest concerns over increasing levels of space debris is the danger of a “runaway” effect. First proposed by NASA scientist Donald Kessler in 1978, the “Kessler syndrome” is a hypothetical situation in which debris collides with itself or operational spacecraft, producing new debris whose numbers grows exponentially, until the process becomes unstoppable.
The result would render portions of orbital space too dangerous to use. Such an event was depicted dramatically in the 2013 movie “Gravity.” Avoiding such a situation is of paramount importance to the future of space transportation.
Flying garbage trucks
The alternative is to actively remove space debris, by redirecting their orbits so that they enter the Earth’s atmosphere and harmlessly vaporize (unless they are so massive that they remain intact until impact). Among the methods proposed to accomplish this include indirect (ground-based) and direct (space-based) approaches.
More than one group is investigating the use of ground-based lasers. Shining an intense laser on an object can create a jet of gas that will change its velocity. The object’s speed only has to decrease by about one percent for it to slow down enough to re-enter the atmosphere. However, this technique only works for smaller objects. NASA estimates that a five-kilogram object could be safely removed using a multi-kilowatt laser over a two-hour exposure.
Methods of contacting and removing space debris include sending “janitor” spacecraft into orbit to attach to an object and pull it back into the atmosphere. Multiple approaches to this concept exist. Another method involves releasing a cloud of inert gas in the vicinity of multiple debris targets; the resulting aerodynamic drag would slow them down enough to re-enter the atmosphere.
Still others are exploring the use of lightweight sails to create just enough drag from the thin atmosphere present at orbital altitudes to achieve re-entry.
While such techniques would not be inexpensive – scientists estimate that a laser system might cost several million dollars to build and operate – satellite insurance currently costs between 5 and 15 percent of a satellite’s value, or tens of millions of dollars each. If collision risk could be lowered through these approaches, it seems that the money is there to pay for it.
Some people are rethinking the idea of cleaning the skies of space junk, arguing that such objects may be more valuable if they stay in orbit, but can be re-purposed. The U.S. Defense Advanced Research Projects Agency is sponsoring the “Phoenix” project to reclaim intact hardware from non-functional satellites for re-use. Others are looking at extracting precious materials directly to use in space-based manufacturing.
Each kilogram launched into space costs an average of 20,000 US dollars, not including the cost of production on Earth. The more than 5,500 metric tons of debris currently in orbit therefore has a theoretical value exceeding 110 billion US dollars. Such materials consist of highly-refined metals, high-performance lightweight composites, and electronics containing precious elements. Examples of materials that can be recycled include aluminum alloys and other metals. Kevlar, a high-strength organic polymer used in bulletproof vests as well as space applications, is five times stronger than steel and can be recycled into new fiber.
However, space materials must meet several performance criteria, including dimensional stability (ability to maintain size and shape under large temperature swings that occur in orbit), mass efficiency (as light as possible without compromising structural integrity), durability (ability to withstand the harsh space environment, including radiation, atomic oxygen and vacuum), and strength or flexibility (the ability to resist or bend under force without breaking).
So it is unlikely that much material, if it could be captured, would be re-used, but if even a small fraction of this material were re-purposed for space-based manufacturing such as 3-D printing, it could be worth a lot of money.
What do you think about the threat of space debris and approaches for removing it? Share your thoughts in the comment section.
Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.