The year 2016 will be the 38th anniversary of one of the most important papers ever written with respect to our satellite population. In June 1978, Dr. Donald Kessler published "Collision Frequency of Artificial Satellites: The Creation of a Debris Belt", in which he explained that the density of orbiting satellites would eventually become so great that catastrophic collisions would not only become possible but inevitable. Although minor collisions did occur in the 1990's and early 2000's, his prophecy became reality on February 10, 2009 when an active American Iridium telecommunications satellite (Iridium 33) and an inactive Russian Cosmos military satellite (Cosmos 2251) collided 800km above northern Siberia. The collision generated at least another 3,000 pieces of debris, which was in addition to the similar amount of debris generated by a very irresponsible Chinese anti-satellite (ASAT) missile test two years earlier that destroyed the Fengyun 1C weather satellite which was also orbiting at an altitude of 800km.
Dr. Kessler predicted that the first collision would occur between 1989 and 2005. Given the incredibly complex probability analysis and uncertainties required to actually predict a collision between two or more satellites, his prediction was very good. Dr. Kessler's work did prompt discussion regarding the eventual removal of dangerous satellite debris; however, to date, none of the discussions have resulted in a working clean-up plan. In other words, few to no pieces of debris have been cleaned up; certainly not enough to negate the debris increase rate. Most notably, Skylab (1979) and the MIR space station (2001) were deliberately de-orbited and allowed to burn up over the Pacific Ocean.
Before the 2009 collision, some had argued that the vastness of space was so large that the probability of collision was negligible. This so-called "Big Sky Theory" might have prevented a more serious clean-up effort, or it might have stifled serious research investment. In the 1970's, the "Big Sky Theory" might have been the correct one; however, as soon as satellites became more commercial in the 1980's and 1990's, Dr. Kessler's fears should have been taken much more seriously.
When I began my journey in satellite tracking in mid-1997, there were nearly 10,000 catalogued orbiting satellites. At the time of this article, nearly 20 years later, there are nearly 20,000. The additional 10,000 satellites are mostly debris caused by the Fengyun 1C destruction and the Iridium 33 - Cosmos 2251 collision. Dr. Kessler had argued early-on that as the satellite density increased, the collision probability would subsequently increase. As the number of collisions increased, so would the collision probability. Over time, a collision cascade would occur, rendering the space above the Earth's surface uninhabitable for any future satellites. This nightmare scenario has been dubbed the "Kessler Syndrome"; named after Dr. Kessler.
I have to admit, I was sceptical of the "Kessler Syndrome" at first. Although I was not a proponent of the "Big Sky Theory", I was hopeful that the first major collision would not occur until the 22nd century. However, since the 2009 collision, I am now firmly in Kessler's camp. After the collision, I wrote a paper that stayed away from analyzing the collision itself (many were doing that already) and focused instead on ways to prevent future collisions through prioritization of space assets, discussing the legal liability of such collisions, and contemplating the future of space surveillance (including satellite tracking). I wanted to know if I could answer the major question, "How can the next collisions be avoided?". My paper raised more questions than it had answers. This is what worried me the most.
Having worked in satellite tracking in one way or another since 1997, I was aware of many schemes to clean up orbiting debris. I also became somewhat sceptical of the schemes about 10 years into my career when I realized that none of them actually cleaned up anything. This has not changed nearly 20 years into my career, despite the calls by many to get serious about space debris and start cleaning it up. Nevertheless, the debris population continues to increase and the calls to clean it up continue to get louder, or at least more numerous.
Personally, I am growing somewhat weary of hearing and reading articles talking about how it is "getting crowded up there", especially since few of these reporters have any idea of how the satellite population is distributed. They report as if every single orbiting satellite is in danger of collision with debris, when this is not exactly true. Comically, some mention GPS being disrupted, when GPS satellites are in the least danger of collision thanks to their unique orbit altitudes. However, launching new (replacement) GPS satellites through the lower-altitude debris might be difficult. I am also getting tired of hearing about new strategies of debris cleanup, only to see these "amazing plans" disappear within a few years, most likely due to lack of funding.
When I read about yet another debris cleanup plan, I see several similarities to its (failed) predecessors:
1) It's cheap!: No, it isn't, and it never will be. The longer we wait to clean up the debris, the more expensive it will be to clean it up. We are talking about thousands of pieces of debris, from a small screw (and smaller) to a full-sized payload. Approximately 90% of the 20,000 (catalogued) objects in orbit are inactive (debris). How can cleaning this up possibly be "cheap", except in the relative sense?;
2) It's easy to implement!: Really? How about getting clearance from the other nations with satellites in orbit? Obviously, real debris de-orbit tests were not conducted or else we certainly would have heard of them. If it was that easy, someone would have implemented it years ago, when the situation was not as dire; and
3) It's effective!: Please. Nothing is "effective" until it has been demonstrated in real life. If one of the debris removal ideas had actually safely removed just one piece of debris from orbit, I would be very hopeful. So far, nothing.
These three claims remind me television advertisements (fast, easy, cheap, effective). This will not work to clean up space debris. If this is the only way to attract potential investors, then no wonder none of these ideas made it past the "drawing board" stage. Cleaning up space debris will be a very difficult and pain-staking endeavour that will need to be conducted by the international community, not just one single nation. In my view, this is just a difficult a task as bringing a human being to Mars and back: perhaps even more difficult since it won't be a one-off accomplishment.
There are definite reasons why I am becoming more sceptical about the possibility of cleaning up space debris, some of which I have included below:
1) China. This is the single most important reason. The intentional Fengyun 1C destruction by a Chinese ASAT missile was simply the most irresponsible act in space (a close second being the littering of space in the first place). The problem of space debris was already well known at this time (January 2007) but the Chinese decided to blow up a satellite orbiting at 800km in altitude. At such an altitude, the thousands of pieces will require decades to naturally de-orbit. In February 2008, the USA shot down one of its own satellites (USA 193); however, that satellite was only about 200km in altitude. Most of the pieces were well below the active satellites' orbits and they fell to Earth within 3 months. There is no guarantee that China (or any other nation) will not do this again. Any debris clean-up effort, no matter how vigorous, would be quickly negated by a single ASAT missile that hits its target;
2) Legal Implications. The satellite population is not owned by a single nation. Today, nearly every nation on Earth has orbiting property in space. If a single nation attempts to remove all debris from orbit, there is no doubt that other nations would protest. They would talk about salvaging rights, risk of damage to their property (regardless if the satellite is active or inactive), and anything else they can think of. The legal problems might be more difficult than the technical ones, especially if the international community is required to green-light any debris-clearing project (especially when using powerful lasers!). What would happen if the debris-cleaning satellite damages another active satellite unintentionally? What if the debris-clearing satellite de-orbits the wrong satellite? What guarantees are there that the debris-clearing satellite is meant only as a debris-clearing vehicle and not involved in some other nefarious exercise? What if a debris-clearing laser strikes and damages another satellite unintentionally, or worse, intentionally?
3) No successful debris-clearing tests to date. This is a big one. Not a single piece of orbiting debris has been successfully de-orbited by any proposed de-orbiting plan. Although it is true that Skylab and MIR were intentionally de-orbited, they both had thrusters on board to manoeuvre them. Most debris do not have active on-board propulsion and therefore have to wait until they are naturally de-orbited (through aerodynamic drag forces) or a well-funded, successful, and reliable de-orbiting plan is effective.
4) International cooperation required. This has been mentioned in 2), but it warrants its own bullet. No debris cleanup plan will succeed until the international community is supporting it. If this was the late 1970's and there were approximately 4,000 pieces of orbiting debris, it might be possible for one nation to clean it up, provided the effort was serious and round-the-clock. However, today's debris population is much too large for any one nation to deal with. If a serious effort is required, then the entire world would need to be involved and international cooperation is essential to minimize the inevitable legal problems.
5) Increasing annual launch numbers. As an increasing number of nations have access to satellites and launch services, an increasing number of launches will occur. The cubesat program alone will allow additional nations to possess their own satellites. Although cubesats are much smaller (and therefore a much smaller collision target) than traditional communication satellites, their eventual increased numbers, due to low cost and ease of construction, will quickly make up for this. When combining the increased number of launches with future ASAT and collision debris, the most optimistic present-day debris-mitigation plans will fall far short.
6) Lack of support and funding. Any ambitious debris cleanup effort would require a large amount of support and funding from international and national institutions and corporations. The major problem with debris clean-up is that it would be mainly invisible to the general public and they would likely not see any benefits in the short term. Debris cleanup is more of a prevention and maintenance effort rather than a brand new technological breakthrough with immediate results and benefits. Unfortunately, today's business is more concerned with immediate results and fast profits rather than funding the prevention of a catastrophe that might occur a number of years down the road.
7) "Out of Sight, Out of Mind" (Big Sky Theory, Part 2). Immediately after the Iridium 33 - Cosmos 2251 collision, there was talk of speeding up efforts to clean the debris from high priority areas, such as the sun-synchronous regions. However, Iridium LLC simply placed an orbiting spare into the slot once occupied by Iridium 33 and carried on as usual, stating that it was just as easy to close your eyes and hope for the best rather than to expend precious manoeuvring fuel to avoid a predicted collision whose uncertainty is too high to trust. Despite nearly monthly calls by the media to clean up the mess in space, many simply do not treat this problem as dire, just as long as the satellites continue to work for us. Even worse, some nations just use the orbiting debris to call attention to their own space projects, including the space surveillance efforts that Iridium LLC once deemed inadequate and inaccurate, when they should be looking at the big picture and cooperating with international efforts to remove the dangerous debris from the "prime real estate" in space. I had once remarked to a reporter after the collision that "the cleanup effort will only become serious when the cost of collision prevention equals the cost of collision loss". The truth is that debris removal is not yet economically viable because it would cost more to clean up the debris than any (eventual) return of investment. However, this is the point. Either we pay now to clean up the mess in space or pay much more later when the collisions and cleanup costs are much larger. A smart business model would see the benefit of cleanup right now and get to work with the knowledge that the profits enjoyed now will continue (and possibly increase) with a cleaner space environment.
Many would see these points as being "too negative". This is a dangerous mindset. Besides, I wonder what some said of Dr. Kessler's work early-on in 1978? It is possible that some thought he was being "Chicken-Little", when in fact he was being very serious. The 2009 collision vindicated his work and finally silenced most of the "Big Sky Theory" supporters.
If the "fast, easy and cheap" solutions cannot be implemented due to any of the above reasons, then what can be done right now that will be effective? One solution that I have been throwing around at a few conferences seems quite harsh, in fact some might think it Draconian to implement. My idea is to declare a worldwide moratorium on satellite launches to the most crowded parts of the satellite population zones, especially the sun-synchronous and geosynchronous (GEO) zones, for at least 50 years in order to allow the low Earth orbit (LEO) realm (below 1000 km) to clear itself naturally. Of course, 50 years will not be enough to clear the zones 800km and above; however when performed in combination with an eventual debris cleanup effort (especially at above 800km), it would ensure that the number of orbiting debris will finally decrease for the first time since the late 1950s.
A launch moratorium would be very painful and would not be fast, easy or cheap. The cubesat effort will likely die as a result, but could be restarted after the moratorium has lifted. The worldwide satellite industries would likely be decimated and would have to retool itself for debris removal research and implementation in order to survive. This assumes that all nations actually abide by the launch moratorium and therefore refrain from launching any satellite for 50 years. Of course, there would be a number of exceptions, such as communications and weather forecasting in GEO. However, the exceptions should only be for high-priority and not for experimental or educational purposes. I am not going to mention how difficult enforcement of such a moratorium would be, especially when considering nations like the United States and China. Although such a moratorium would be very painful today, our satellite population would be much safer by the end of it, especially if a vigorous and effective debris removal effort is happening in the meantime.
Of course, my opinion
about debris cleanup might be wrong, but the ever-growing satellite population
increase and increasing calls for debris removal is evidence that something
effective will have to be done right now. A launch moratorium would at least be
an effort that can be implemented quickly. This is one area where I hope that I
am wrong and that a new reliable and effective debris removal method will be
cleaning up debris in this New Year and that in several years the "Kessler
Syndrome" will be a distant (but not forgotten) memory.
Can This be Cleaned Up? Was Last Modified On January 02, 2016