Author: Taewoo Kang
Mentor: Dr. Jasna Jankovic
Stamford American International School
This report explores and discusses space debris, or space “junk” – its origin, how it affects the Earth and solutions for debris management. Nowadays, space debris, which is made from “dead satellites” and meteoroids, is one of the biggest global issues that we have to solve immediately. Scientists are trying to solve this problem by detecting space debris by using lasers and telescopes. They are working to solve the issue by planning to charge orbital use fees and using disposal orbit so that they could reduce the amount of space debris in the Earth’s orbit.
What is space junk?
Space junk, also known as space debris, is any piece of machinery left by humans in space. The majority of orbital debris is made up of human-made materials, such as fragments of spacecraft, tiny flecks of paint from a spacecraft, rocket parts, defunct satellites, or pieces formed through explosions of objects in orbit, floating around in space at high speeds.
The majority of space garbage travels at a breakneck speed of 18,000 miles per hour, almost seven times faster than a bullet. Present and future space-based services, explorations, and activities pose a safety risk to people and property in space and on Earth due to the rate and amount of debris in LEO (Low Earth Orbit).
History of space junk
Over 6050 launches in the past 60 years have resulted in approximately 56450 monitored objects in orbit, of which approximately 28160 remain in space and are continuously tracked by the US Space Surveillance Network and stored in their catalog, and these kinds of debris weight more than 9300 tons in total. About 70% of space debris in LEO was created by China, America, and Russia.
For example, in 2007, China launched a ballistic missile from the Xichang Space Launch Center that destroyed a satellite called Fengyun-1C (FY-1C). This had produced the largest space debris generating event in the Earth’s orbit on the record. More than 3000 pieces of debris were produced and 97% of them are remaining in orbit. Moreover, scientists have estimated that 32000 smaller pieces haven’t been tracked yet. 
Another event was in 2009. There was a big collision between the Russian satellite (Cosmos 2251) and the US satellite (Iridium 33). Figure 1 shows Cosmos 2251 satellite which produced 1357 pieces of debris and Iridium satellite has produced 528 pieces of debris. Scientists have estimated more than half of the Iridium debris will last at least 100 years in space, while most of the Cosmos debris will last at least 20 to 30 years. The picture below is showing how Cosmos 2251 and Iridium 33 have collided.
Figure 2 shows the history of space junk production and its composition. As it can be seen in the figure, most of the space debris originates from dead and leftover satellites. Moreover, like Cosmos and Iridium satellite collisions, about 9% of space debris is produced because of collisions between satellites.
What kind of debris?
Space debris consists of more than 10 thousand artificial space objects and natural materials. Now, what kind of materials are in the space debris? Most of the space debris consists of natural materials such as meteoroids and human-made materials such as space rockets and satellites (shown in Figure 3).
First off, a natural material meteoroid is a solid object that travels through interplanetary space that is larger than atoms but smaller than asteroids. It travels around the sun with velocities ranging from 11 km/s ~ 72 km/s. Since they move by gravity, they sometimes get into the Earth orbit and become a part of space junk 
Secondly, debris from space rockets and satellites are types of artificial materials. More than 10 thousand of these debris objects have been placed into space through more than 6000 rocket and satellite launches, out of which only about 3900 are operating. The main reason satellites produce space debris is that they are in either collision or explosion called in-orbit fragmentation. The most common cause of in-orbit explosions is leftover fuel in tanks or fuel lines and other energy sources that remain on board after a rocket stage or satellite has been discarded in Earth orbit. The harsh space environment can wear down the mechanical integrity of external and internal parts over time, resulting in leaks or mixing of fuel materials, which can lead to self-ignition. As can be seen in Figure 3, most of the debris is the pieces of dead satellites.
Humans just leave those kinds of satellites in space since the cost is very high to bring the “dead” satellites into the Earth. Additionally, due to lots of missions to space, there are many discarded parts of the rockets that end up in local space. This material can range in size from a discarded rocket stage to microscopic paint chips.
How do scientists count or track space debris
There are two ways to detect space debris from the ground. One is to use lasers and the other method is to use a telescopic detector and filter.
Using a laser with a kHz repetition rate was the initial method to detect space debris. The way scientists detect space debris with laser tracking method is first, they detect space debris with an optical telescope and at the same time, they send laser pulses to the debris so that the distance to the object is calculated by the time which laser travels to the debris and comes back. By combining the time measurement and position determination, scientists can determine the approximate position and size of space debris
Laser observations of space debris structures have been carried out since the turn of the century. However, this approach only operated for a few hours at dusk, when the detection station on Earth is dark and the debris is still lit by the Sun. Figure 4 shows how a laser can detect space debris. 
Secondly, scientists use telescopes to detect space debris which is placed in GEO (geostationary earth orbit). For example, in European Space Agency, Zeiss 1M telescope is operated in Spain, as shown in Figure 5, which is used for investigating the property and characteristics of debris in space. This telescope can detect debris, whose size is down to 10~15 cm. Moreover, it is capable of determining the color of the debris which is very important since it allows to determine material property and provides an information of the origin of the detected debris.
How space debris can affect Earth
Space debris can affect Earth in many ways, mostly negatively. Collisions with active spacecraft are the biggest issue. Any piece of debris greater than 1 cm in diameter will cause a catastrophic impact with an average impact speed of 10 km/s. Collisions between debris and operational satellites cause not only financial but also environmental damage. In the event of a collision, a satellite’s ability to correct its orbit will eventually be lost, and it will become another space danger with no way to steer into a more stable orbital direction. This raises the likelihood of a damaged satellite colliding with another orbital target, such as another satellite or debris, and restarting the debris generation cycle. The more debris in space accumulates, the more likely another collision will occur, adding to the issue. 
Moreover, there is a possibility of dead satellites reentry into Earth orbit. As it can be seen in Figure 7 when the dead satellites re-enter the Earth’s orbit, the break-up starts at around 78 km altitude and this is called the reentry interface. Since the satellite is affected by the wind when re-entering to Earth orbit, the pieces which have low mass but large areas such as solar panel sheds first. Then the catastrophic breakup begins when the time passes and finally leads to a major breakup where all the things are divided into small pieces. These pieces move 50 m/s which means when they reach the ground they will have a massive power.
Another aspect of space junk’s effect on Earth is the weather. The effect on the weather isn’t direct, however, if the density of the debris increase to the point where it interfere with our ability to use weather satellites it distracts tracking weather changes caused by our ground-based pollution.
Finally, space debris could fall from the sky and threaten our communities. On average, about 200-400 pieces of debris fall from the sky and enter Earth’s atmosphere every year. Fortunately, since human populations live on a small percentage of the total Earth surface, falling debris is likely to fall into the ocean.
Proposed solutions for debris reduction or removal
One proposed solution for the space debris problem suggested in the literature is to charge operators an “orbital use fee” for every satellite in the Earth’s orbit. According to economist Matthew Burgess, a CIRES(Cooperative Institute for Research in Environmental Sciences) Fellow, and co-author of a recent report, orbital usage fees, if implemented, would boost the space industry’s long-term value. An annual fee of around $235,000 per satellite would quadruple the value of the satellite industry by 2040 by reducing potential satellite and debris collision risk. In another study scientists have predicted the effect of charging “orbital use fee”. As Figure 8 shows, the number of satellites launched and satellites placed in the low earth orbit will be reduced, collision probability between satellites will be decreased dramatically and finally the amount of debris will be also decreased. This shows that charging “orbital use fee” will give a positive impact
Another proposed solution is to deorbit space debris into so-called “disposal orbits.” Re-orbiting items into disposal orbits at the end of their usable lifespan is one method of extracting them from the most commonly used high-altitude orbital regions. This keeps the objects in Earth orbit, but it keeps them out of areas where they could collide with working spacecraft. However, when a space object is moved into a disposal orbit, the collision danger in its original orbital region is reduced, but the collision hazard in the current orbital region is increased. Objects transferred to disposal orbits, on the other hand, may still contribute to the debris hazard in their original orbit because debris created by collisions or explosions in disposal orbits can overlap the original orbit. Moreover, the process to deorbit or accelerate the orbital decay of spacecraft or rocket bodies would be expensive.
Finally, spacecraft designers, on the other hand, should take a system-level approach to avoid unintended spacecraft breakups. The strategy is to first identify all possible sources of stored energy on a spacecraft nearing the end of its operational life; second, provide a method for benignly dissipating the stored energy satellite for each source; and third, enable these means at the end of the spacecraft’s functional lifetime. 
In any case, there is no way to prevent all potential spacecraft breakups: despite precautions, a small number of spacecraft breakups would continue to produce debris, but at a lower level.
One solution I have come up with to solve the space debris problem is to create a giant magnetic spaceship. Most of the space debris consists of satellites that are human-made and most of those satellites consist of some metallic material. This means some of the space debris is magnetic. Thus, if we could use a magnet which could attract all the leftover dead satellites, and remove them from the earth orbit, we could get rid of some of the space debris.
To be specific, we could create a magnet spaceship where all the surface of the spaceship is covered with a magnet. The spaceship is going to travel around the low earth orbit and attract magnetic space debris on their surface which pilots are controlling on the earth. If the surface of the spaceship is full of debris, pilots are going to remove all the debris from the surface into the spaceship by using a strong massive vacuum cleaner which automatically cleans the surface of the spacecraft and stores it inside it. Then, there will be another machine in the spacecraft which compresses all the absorbed space debris into small square pieces so that there will be more space to store the space debris. When the spacecraft is full of space debris, pillot will send it back to the earth so that we can recycle and reuse it.
In summary, space debris problems are treated as a serious global issue. More than 34000 pieces of space debris are orbiting around earth and these have extremely negative effects on the Earth: collision between space debris and satellites, re-enter the Earth orbit and disturb tracking weather change. One of the biggest incidents that have produced massive amounts of space debris was a collision between Cosmos 2251 and Iridium 33. In order to get rid of this space debris, scientists first have to detect them. The way they discover space debris is by using laser and telescope. After they recognize the space debris, scientists plan to charge a fee for orbital use so that companies could reduce using satellites. Also, they work to send the space debris to a disposal orbit. This process is significant for reducing the amount of space debris and clearing up the Earth’s orbit.
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