By: Scott Castenson, Bradley Mortensen, Bethany Weeks
Space debris is an inevitable byproduct of space travel. According to David Wright, senior scientist and co-director of Global Securities at the Union of Concerned Scientists, space debris "is any man-made object in orbit that no longer serves a useful purpose" . Eric Wetzel, chief engineer at Andrews Space Inc. adds to that definition by saying space debris is, “any object in space that is not controlled.” This debris can be: natural meteors, minuscule paint flecks that have come off satellites or shuttles, tools neglected by astronauts, depleted rocket stages, blown off hatches, non-operational satellites, or pieces from explosions and collisions with existing space debris [1, 5, 17]. Space debris is an issue for space travel as it is dangerous as well as prolific. While large collisions are rare, they have occurred, proving space debris is a problem. However, ever since space debris became an issue, space faring countries and international organizations such as the Inter-Agency Space Debris Coordination Committee (IADC) and the International Organization for Standardization (ISO) are working to come up with solutions to reduce the probability of space debris causing damage on operational space vehicles [3, 10].
Space Debris Origins and Growth
On October 4, 1957, the Soviet Union launched Sputnik 1, the first satellite to orbit earth. It was also the day that the first piece of debris was left in orbit . Space debris comes with every launch into space. With over 4,000 launches since then, debris has begun to build up in earth's orbit . Figure 1 is a NASA rendering of where debris is located around Earth. Each dot is not to scale but represents a trackable piece of debris. In 2003, 10,000 pieces of debris larger than ten centimeters were categorized and their sources determined (see Figure 2) . Currently, NASA estimates the total number of debris that are larger than ten centimeters to be over 500,000. [5, 20, 11].
Currently, there are few ways to dispose of space debris. We can try to de-orbit decommissioned satellites to burn up in the atmosphere. However, this must be addressed before satellites are even launched. Most of the time, debris can be moved into a less desired orbit [5, 7]. There is also a natural waste disposal process caused by the earth’s gravity. Space debris gets pulled in by gravity and loses orbit, burning up in the atmosphere . Debris in an orbit of 600 kilometers above sea level or lower generally de-orbits within several years upon decommission. Debris between 600-800 kilometers de-orbits after a couple of decades, but anything above 1,000 kilometers will take at least a century to lose its orbit . This natural de-orbit was able to keep up with the debris created at the beginning of the space age.  However, since the 90’s we are creating more debris than the natural process can de-orbit. 
Debris re-entry into Earth’s atmosphere poses a small threat. Most of the time, debris burns up upon re-entry, but there have been cases where pieces re-entered without completely disintegrating. In most of those cases, pieces just land harmlessly in the sea or, less often, on uninhabited land like Australia’s outback . However, there have been a few specific cases when pieces landed and caused damage to a populated areas. The damage is generally small; in England a piece of debris caused an extra hole in a golf course, and once a spray of debris put holes in a roof of an English house . However, a piece of space debris has never killed or hurt a person on Earth.
All this debris is not just sitting still in orbit, but is constantly in motion. This poses a serious threat. The average speed of space debris is 10 kilometers per second. Even a flake of paint less than 1 centimeter in diameter has potential to harm as it has a velocity that is ten times of a fired bullet [20, 11].
These speeding pieces are also difficult to track . Only objects over 10 centimeters can be tracked and are done so by organizations like the North American Aerospace Defense Command (NORAD)  However, these organizations only vaguely know where in space these pieces are. As a result, it has been estimated that 90% of the time a vehicle is maneuvered, the debris to be avoided was not actually there.  Anything smaller than 10 centimeters cannot be tracked.  It is estimated that there are over a million pieces of debris in this category. 
Accidents and Collisions
The biggest accident caused by space debris occurred between a decommissioned Russian military Kosmos satellite and an Iridium communications satellite in 2009 . They were moving about 11.6 kilometers per second relative to each other and the collision completely destroyed both satellites [14, 15]. This added over 10,000 pieces of trackable debris . Because of the orbit the satellites were in, their debris now poses a threat to the Hubble Telescope . Another large debris contributor was in 2007 when China did an anti-satellite test on a retired low earth orbit meteorological satellite [7, 11]. China sent a rocket to destroy the satellite, which resulted in an increase of debris by 9-10% . That June, NASA had to maneuver their environmental satellite, Terra, to avoid the debris from the result of China’s test .
The most common collisions, however, are from small debris like paint flecks which have been known to put 5 millimeters deep pits into the windows of space shuttles and stations . The windows have needed to be replaced several times because of this problem . The Hubble Telescope has also suffered damage to its aft shroud and thousands of craters have been found on its solar array .
Other space debris accidents have included:
Voyager 1’s scan platform jammed - Feb. 1979 
Yanktar 4k2 exploded - June 1985 
Navstar 6 hit and lost one month of life - July 1987 
A French satellite hit and damaged by an old exploded French rocket - 1996 
Sefra hit and as a result a large portion broke off and re-entered Earth’s atmosphere - April 2002 
What Can Be Done
Many proposals have been made for what is the best method to control and reduce space debris. The Japan Aerospace Exploration Agency (JAXA) has proposed a space debris remover that actively removes debris from its orbital . In contrast, the IADC and the ISO have proposed solutions in the form of international laws and regulations for space flight [3, 10]. Dependence on only active removal of space debris may be extremely costly, while strict regulations may inhibit innovation and make space travel prohibitive for some countries. Neither debris removal nor regulatory laws by themselves will effectively control space debris while still allowing for space travel to continue. A combination of binding international regulations to slow the creation of space debris and the employment of devices that actively removes debris will lead to the most effective control and safe reduction of debris in space.
Active Removal of Space Debris
JAXA has constructed and is testing a multiple space debris remover (MSDR), which can attach to any vehicle or satellite traveling into space. This system is equipped with a navigation system, tracking system, robotic arm, and an electro-dynamic tether (EDT). The MSDR is built to remove up to ten items of debris from their orbits, the last being itself. The debris is moved to an orbit that poses less of a threat to operational satellites and space vehicles. The general manner in which this device achieves this feat is by the following :
1. Device locates debris for removal using navigation and tracking systems
2. Once locked onto the target, stops the rotational movement of the debris using a robotic arm
4. EDT uses electrical currents and the planet’s magnetic fields to produce a force thrusting the target out of its orbit 
More research needs to be done on MSDRs to see if they are a viable solution to space debris removal. If they can accomplish what JAXA intends, then MSDRs will be an integral part of the solution to space debris. Unlike other proposed solutions such as shooting down space debris, MSDRs do not create more debris. At the end of this process, there is always less debris in orbit than before.
International Laws and Regulations
Even though international laws and regulations on space travel do not play as active of a role in the removal of space debris, they are imperative to slowing the creation of more debris. The IADC and ISO have been working on international regulations for space faring countries so that space debris is reduced . The IADC is an international forum in which space faring countries draft international guidelines to be considered in the manufacturing process and launching of all spacecrafts to minimize space debris. Where the IADC states what should be done, the ISO comes up with how these specifications for spacecrafts should be achieved. The ISO is still in the process of drafting solutions for manufacturing and launching spacecrafts. The problem is that the ISO’s regulations are non-binding by nature [3, 10]. This is unacceptable. For an international organization to have power and be effective, regulations must be binding so that all nations follow the same code of conduct. This will help to avoid disputes among countries that may have different space regulations. For instance, even within a country there are several organizations with their own lists of rules and regulations for space travel. In the United States, the United States Government (USG) has Orbital Debris Mitigation Standard Practices while NASA and the Department of Defense have their own regulations . To avoid confusion within countries and between nations, a binding international law should be created for space travel.
Space debris has been an issue ever since the beginnings of the space age and will continue to be one until every unused man-made object in Earth’s orbit is removed. It is an issue that must be addressed by all space faring nations of the world. We need more support and solutions like ones posed by JAXA as well as an agreed upon set of regulations to ultimately reduce and eliminate our creation of space debris.
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