In 1996, a French spy satellite called Cerise was orbiting several hundred kilometers above earth when suddenly a heavy object, about the size of an average suitcase, appeared out of the darkness and crashed into the satellite at a violent speed. Cerise was seriously damaged, and an antenna several meters long was snapped as easily as a flower stem. The object that hit the satellite was a piece of metal that had broken off a French missile called “Ariane” ten years earlier, and had been drifting around in space undisturbed ever since.
For example: the average speed of an object on a low course around the Earth is about seven kilometers a second – roughly ten times the speed of a pistol bullet. The kinetic energy (the mechanical energy that a body has by virtue of its motion) rises according to the object’s squared speed. This means that if a tiny object the size of a pistol bullet strikes a space shuttle at a low orbit the impact will be a hundred times stronger that of a bullet fired on the shuttle from a gun. In other words, an object the size of one hundredth of a bullet could harm the shuttle to the same extent as if it was shot from a firearm at close range.
For example, take the Soviet spy satellites of the RORSAT series, which were launched one after another for many years, from 1967 to 1988. Their objective was to track NATO movements via radar waves. The return of the radar waves to the altitude in which the satellites were orbiting was very low, as expected, and therefore the RORSAT satellites were stationed on an orbiting course very close to Earth, at an altitude of only a few hundred kilometers. The low orbit prevented engineers from using solar panels to supply energy for the spy system: The proximity to the atmosphere would cause the solar panels to serve as sails that would cause the satellite to lose speed and fall. Therefore, small nuclear reactors were used to provide the satellite with electricity. The problem with nuclear reactors is that you can’t let them burn in the atmosphere when the satellite’s life is over – the radioactive material will spread and pollute the atmosphere for years. The method for getting rid of the nuclear reactors was to toss them far away from Earth, and in order to do this it was necessary to rise to a higher altitude. This solution is still an acceptable one today, and we will elaborate on it shortly. In order to push the reactors to a higher altitude course, an energy source is required, and therefore the mass that we want to move should be as small as possible. To that end, before sending the reactors to the route far from Earth, soviet engineers on Earth opened the faucets on the satellite and let the cooling liquid of the nuclear reactors spill into space. This might have made sense from an engineering point of view, but was a disastrous move in the long term as hundreds of kilograms of cooling liquid mixed with large and small metal pieces were dumped into orbit around Earth, many of which still constitute a danger to this day.
The Americans have their own part in the foolish conduct in space, and in this case as well – the road to hell was paved with a wall to wall carpet of good intentions. In the 1950s, before the satellite age, most of the classified military communications were conducted via underwater cables in the oceans. The American generals were concerned that during the war the Russians could simply cut these cables and searched for a means of communication that couldn’t be sabotaged. Someone in the Defense Department came up with this bright idea: Let’s send a million tiny needles into space, where they will orbit in a circular route at an altitude of 3700km. You can probably guess by now where this story is heading… The idea was that the tiny needles, each only half a centimeter long, would create a “metal belt” around Earth (called “West Ford Belt”). If radio waves suited to the length of the needles (8 gigahertz) were transmitted, they would bounce off the needles and return to Earth, thus enabling uninterrupted radio communication around the world.
Undoubtedly, this was a great idea, which even proved to be useful when put into practice: The needles were distributed on the desired course, and the Americans were able to conduct successful long distance radio transmissions. At that time (the early 1950s), the satellite communications world was just developing, and the satellite proved to be an excellent substitute for the metal belt: Performing the same function, but far more efficiently. The satellite is an active device: It receives radio waves from Earth and is capable of enhancing them or changing their frequency, determining the transmission strength and returning quality communication. The Westford Belt, on the other hand, was just a bunch of utterly passive needles. It is obvious, therefore, why the idea was quickly abandoned, and we were left with four hundred eighty million needles to try to evade. A substantial amount of these needles have fallen to Earth, but there are still many left in Earth’s orbit.
The figure I mentioned earlier, half a million pieces of garbage in space, refers only to the pieces larger than one centimeter in length; there are millions more pieces out there that are smaller but no less dangerous. Over the years, about sixty windows have been replaced in different space shuttles due to scratches and deep dents caused by the impact of these small pieces. In one of the gravest incidents a collision with a paint particle one millimeter long almost completely shattered a window in a space shuttle and left a dent several centimeters wide on the pane. If this particle had hit an astronaut while spacewalking, for example, it would have almost definitely torn his spacesuit.
So what can be done? Not much. For the past several years, the American military has been using telescopes and radar systems to track about three thousand particles roughly larger than tennis balls, mainly so that they won’t accidentally confuse them with nuclear missiles, a mistake that could be costly to us all. When one of these large objects nears a space shuttle or space station, the astronauts use evasion techniques and change their course. This is a problematic solution, to say the least, as there is a limit to how many particles can be tracked and the statistics are never in our favor.
Another solution is passive protection of the space shuttles. The “impact shield” is one example of this: the idea is simple but smart. Instead of making the side wall of the shuttle out of one solid layer of sealed material, the wall is built of several adjacent layers, with tiny gaps between them. When a small particle, like the paint particle that almost shattered the space shuttle window, collides with this side wall the collision creates intense heat which partially melts the particle. When the particle passes through the exterior wall layer and reaches the next internal layer, it is already in a liquid state and spreads across a larger area. The large area (still only a few square centimeters) means that the collision pressure is reduced and the wall remains intact. The efficiency of the waffle shield is limited to small particles only, of course, and a piece of metal the size of a golf ball will still pass through the wall, smooth as butter, and probably even emerge from the other side of the shuttle. I wouldn’t want to be an astronaut in the space shuttle when that happens.
Scientists are aware, of course, of the serious problem that garbage in space presents. Different suggestions have been made as to how to clean space of all this junk. For example, one method suggests using laser rays that will destroy the big pieces or divert them to a self destructive course via a return to Earth, while the smaller pieces will be evaporated. Another suggestion entailed large jelly sails that will float in space and gather the garbage pieces. Many more varied solutions have been raised, all of which have one thing in common – nobody will invest the billions of dollars necessary to carry them out. A well known saying states that the difference between genius and foolishness is that genius has limits. Foolishness has played a large part in the polluting of space.
Fortunately, the authorities have realized the dangers in this pollution, and all the space agencies are now trying to minimize the expansion of this problem. One of the common methods for this is the “graveyard route.” Every commercial company requesting a permit from the US government to launch a satellite must design the satellite so that at the end of its life, it is sent to a course far away from Earth so as not to endanger another satellite or space shuttle. This system is highly effective, but only for satellites that are situated far from Earth anyway (such as GPS or communications satellites) so that there is no need to invest a great amount of energy into sending them to the “graveyard route.” There is still no easy solution for satellites on closer orbiting courses and they may stay on their course dozens of years before falling back to Earth.
Even so, there is some progress in the right direction here. In the past, no one made any effort to get rid of satellites at the end of their lifespan. The main concern of the engineer then was to ensure that if the satellite did return to Earth, it wouldn’t fall on anyone’s head. This is no easy task, and the astronauts in the first space shuttle didn’t know (or had only a rough idea), where they would fall when they returned home. John Glen, the first American in space, took a note up with him into space in which the following message was written in several languages: “I am a foreigner from the stars and I come in peace. Take me to your leader and you will receive an immense reward in the eternal life.” Later, Glen explained that he feared he might fall into the hands of a primitive tribe in the Pacific Ocean, and when this happens in the movies the “space creature” always says, “Take me to your leader.”
However, not everyone is equally concerned with the problem of garbage in space. On January 11th, 2007, the Chinese launched an experimental missile against satellites. The missile climbed to an altitude of eight hundred kilometers and then located its target: an unfortunate Chinese weather satellite. The missile and satellite moved opposite each other at a relative speed of eighteen kilometers a second, and the strike was precise: all that was left of the satellite and the missile were thousands of tiny shards and fragments, and within a few weeks a ring of fragments surrounded Earth, much like the beautiful colorful rings of Saturn. Other nations were, understandably, very dissatisfied with the results of the Chinese experiment. Diplomats strongly disapproved of this “step up” in the arms race and the strengthening Chinese threat, but it was obvious that in this disapproval they displayed hypocrisy. The Americans have consistently adamantly opposed the treaty banning weapons experiments from space, and have themselves conducted several such experiments involving missiles against satellites. However, the Chinese experiment was the most polluting incident ever in space, and at least one satellite had to be diverted from its course to evade danger.
The Kessler Syndrome is a theory raised by the scientist, Donald Kessler. According to Kessler’s calculations, even if we were to stop all launches into space today, all at once, the amount of garbage already accumulated has reached a critical mass. The mechanisms most responsible for the pollution of space are the collisions and explosions – each collision between two objects results in thousands of fragments scattered in space; these will then go on to collide with other objects, creating further collisions. Within a few decades, Kessler hypothesized, the inevitable collision between pieces of garbage already out in space today will fill up space with countless dangerous particles. The particles will form a fatal cloak around the Earth, which will completely obliterate any possibility of going out into space. If this prophecy comes true, we might find ourselves in a situation in which entire generations on Earth will not be able to develop advanced space technology, which will have a serious negative impact on technology in general.
About the author: Ran Levi has a B.Sc in Electrical Engineering from the Technion- Israel Institute of Technology. He has published a book about the history of Perpetual Motion Machines, and writes about various scientific and technological issues.
More columns by Ran Levi can be found here.