It has been recognized that the Space debris is one of the most critical problems, which faced the space exploration and scientific research in space. Orbital debris removal has become a very critical part of the commercial and scientific space. Space debris is the problem of this century and this problem is growing non-stop. There are more efforts and new ways which are tried by the space scientists and NASA or other committees which take this into concern. There are many orbit and non-orbit masses which cause space debris. Therefore, there should be new ways and inventions for cleaning and avoiding the space debris problems. Many companies’ associations are trying to find out new research and new effective ways to avoid aggravating this problem. Until now none of the ways is working well because the problem needs many years, as well as effort to be more effective, therefore more useful in cleaning the space. The problem would affect the earth also and other space scientists and space missions to do their work well. Working in the space debris problem will be more important in the future because there are more research and space missions, which are growing more and more, and the countries are working to find out the space.
The problem should be viewed from different aspects. It shows that there are many new ways to innovate, which use robotics science and artificial intelligence to work in new projects that look for new solutions to the biggest critical problems. These new projects in the situation of remote control of machines to solve problems and to let the machines work instead of people in these missions. The new scientific methods to solve humanity and to work seriously in the big critical problems can be used to get these problems solved better in these new projects. There should be special centres, which provide machines, and robots that can be programmed in the new codes to work in the right ways for solving the space debris spread in the space. One more solution could be using spaceships, a special washer or collecting methods or kind of remote control to washout or clean these space debris. These are some solutions, which are random thoughts, and it needs much work and effort to do it.
Space debris must be considered as a serious problem for operational space missions. This can affect many things like the weather of planets, or the space exploration missions in the future.
One of the biggest challenges for space scientists nowadays is space debris removal missions and there are many new inventions on this side and some of them are in progress. In my opinion, working in developing the methods of space debris removal needs many cooperative efforts from many countries and it may take many years until these projects work and become successful.
Methods of Space Debris Removal
2.1 Laser-Based methods
LASER (Light Amplification by Stimulated Emission of Radiation) is very different from a flashlight or a light bulb. It is a special light source that generates a very thin light beam. This form of light is useful for a wide variety of technology and equipment, for instance several methods of space debris removal have been suggested along the past years, many of them were laser-based methods (most not implemented) .
The idea of using lasers to remove orbital junk is not new. In the 1990s, a laser broom project was proposed (Project Orion) and was estimated to cost $500 million. It was a powerful ground-based laser with a high-resolution detection system, that could remove all space debris whose mass is less than 500 kilogram and with size larger than 1cintemeter, within 1000 kilometres altitude, in 4 years only, as Phipps mentioned in his research .
The time-milestone graph summarizes the achievements of human in the past few years.
Figure 1. Milestones achieved in the laser-based methods 
Laser broom or Laser beam as some scientists call it, is a ground-based system that uses laser radiation to ablate space debris out of Earth orbit, by heating one side of an object, or, by reducing its velocity. Therefore, it is known as an altitude. This will change its path for a direct re-entering the atmosphere of Earth and burn or leave Earth’s gravitational field. . This would help reduce Kessler syndrome , also called Kessler effect (Collisions between objects could lead to a cascade
in which each collision produces space debris, which increases the probability of further collisions) .
A new method that uses lasers to ablate space debris was proposed recently, which is called Laser Orbital Debris Removal (LODR). Basically, it is a ground-based system. LODR is the most effective way in terms of cost to mitigate space junk problems. It is going to be a multiuse, it will not only be restricted to space debris and it is the only solution proposed that is useful for both large and small space debris. To operate and build such a system, international cooperation requirements must be met .
Despite all the advantages the laser-based methods have and all the other proposed systems, some research teams and scientists showed that the risk of new space debris generated when the powerful laser breakdown objects is high, which leads to Kessler syndrome. Moreover, it is not guaranteed yet that it would hit the desired target as objects are moving fast and the system is not that accurate .
Regarding the laser-based methods. Some scientists have suggested using autonomous laser beams rather than the traditional way, which is the ground based system, since it is not guaranteed that it would hit the aimed object , furthermore, robots are known to be more efficient and accurate doing that. Many proposals and ideas have been made, to replace the ground-based system on a space vehicle to guarantee that it would work, and it would be less expensive.
The figure shown below summarizes the laser-based methods in a simpler way. Figure 2. Highlights of laser-based methods 
2.2 Net-capturing methods:
To reduce the debris in the GEO orbit, ESA has supported the Robotic Geostationary Orbit Restorer (ROGER) whose goal is to transport the aimed
objects to outer space. The final effector in this project may be either a net or a grip system. The system consists of four flying weights at each corner of the net. The flying weight is often called a projectile, which is fired by a spring device called a net gun. These four bullets help to extend the wide net, winding up the target. It is not important to know the inertia, mass, and other physical figures during the process. ESA also issued deorbit project, which they are confident to declare. It may be the first in flight demonstration of active space debris mission Net cap. The Turing process is one of many ADR principles proposed in the e. Deorbit project .
The advantages of Net Capturing are allowing a large capturing distance, reduced requirements on precision, compatible for different size debris, furthermore, it reviews research areas that are worth exploring under each capture and removal process. Frameworks for methods for the capture and retrieval of space debris have been created. The benefits and limitations of the most important methods of capture and removal are also discussed. In addition, explanations and current programs relating to these approaches are illustrated.
Space debris specimens, in general, lack usable functionality and are reluctant to collaborate. Monitoring failures can occur in loading and momentum transfer during the capture phase because the conditions for capture are not favourable in these cases. In most situations, the target’s detailed mass and inertial characteristics are unclear, either due to a lack of configuration information or due to modifications because of damage suffered during failure or progressive deterioration over time. This in turn, makes impedance matching of the capture arm force control device is impossible.
The aim of this paper is to develop a technique and control scheme for catching and stopping a tumbling, non-cooperative target space debris. To minimize the rotational rate of the target debris. A new brush style contactor was suggested as the end-effector of a robot arm. Most of the debris remains in low Earth orbit, within 2,000 kilometres (1,200 miles) of the Earth’s surface; however, some debris can be located 35,786 kilometres (22,236 miles) above the Equator in geostationary orbit. By 2020, the US Space Surveillance Network had tracked over 14,000 fragments of space debris with a diameter of more than 10 cm (4 inches).
There are some 200,000 fragments between 1 and 10 cm (0.4 and 4 inches) in diameter, and millions of pieces smaller than 1 cm, according to estimates. The time it takes for a piece of space debris to come down to Earth is determined by its altitude. Objects that are less than 600 kilometres (375 miles) in diameter circle the Earth for several years before re-entering the atmosphere. Objects orbiting at more than 1,000 kilometres (600 miles) have been doing so for decades. The volume of waste in space poses a danger to both crewed and non-crewed space flight. A space shuttle colliding with a piece of space debris has a one-in 300 chance of happening (Missions to the Hubble Space Telescope have a 1 in 185 probability due to its higher and more debris-filled orbit). If a known piece of debris has a better than a one-in-a-million risk of colliding with the International
Space Station (ISS), the astronauts conduct a debris avoidance manoeuvre, which raises the ISS’s altitude to prevent collision.
It was the first operational spacecraft collided with space debris when a piece from the upper stage of a European Ariane rocket collided with Cerise, a French microsatellite, on July 24, 1996. Cerise was hurt, but she was also able to react. The first collision that destroyed an operational satellite happened on February 10, 2009, when Iridium 33, a communications satellite owned by the American company Motorola, collided with Cosmos 2251, an inactive Russian military communications satellite, about 760 km (470 miles) above northern Siberia, shattering both satellites.
2.3 Robotic arm
A robotic arm is a type of mechanical arm that resembles a human arm. Its first use was in Britain and have 7 types of arms: Gantry robot, cylindrical robot, polar robot, SCARA robot, articulated robot, parallel robot, and anthropomorphic robot.
Gantry robot: used for pick-and-place operations, seal application, assembly work, machine tool handling, and arc welding .
Cylindrical robot: is used for assembly operations, machine tool handling, spot welding, and die casting. It is a robot whose axes form a cylindrical coordinate system. Polar robot: is used for machine tool handling, spot welding, die casting, grinding machines, gas welding, and arc welding. It is a robot whose axes form a polar coordinate system .
SCARA robot: used for picking and positioning, packing, assembling, and handling machine tools. This robot is equipped with two parallel rotary joints to ensure alignment in one plane. Parallel Robot – One use is the hand-held platform that operates the cockpit flight simulator. It is a robot whose arms have parallel prismatic or rotating joints .
Articulated arm robot – Used for assembly processes, die casting, grinding machines, gas welding, arc welding, and spray painting. It is a robot whose arm has at least three swivel joints. Anthropomorphic Robot-It is built like a human hand, i.e., with single fingertips and thumbs .
The advantages of using a robotic arm in space work or in factory’s are a lot. For example the robotic arm in factory’s help to increase the manufacture of goods and decrease the work time, the use it in building cars, phones, and others thing but in space work they use robotic arms instead of sending a human to space it will be so acuter and easier to use they put it in space mission to catch a pieces of constellations that will increase the information of the space and in other words it will help them to catch the old satellites and spacecraft to return back to earth to get recycle and use in other missions
One of the disadvantages of using a robotic arm in factories is losing control of it which will damage the product. If the electricity of the factory is lost, the work will stop and the company will lose a lot of money, but in space the situation gets
worse, because it can lose the signal from earth and the mission will end. It will end up with a failure flag or it will get the signal again but the strength of it is small. Apart from that is the delay from earth to the space, because it will make the mission slower and harder to work. Sometimes, the delay can change the command that is sent to the ship and rode the mission.
In conclusion, space debris is a serious risk that threatens our planet and the future launching missions. Our team believes that space agencies must concentrate on this topic, as it reduces the number of failed missions and saves satellites on orbit now, such as the International Space Station (ISS). Furthermore, it is a good investment that would help future generations in terms of exploring space and sustain a clean orbit. However, we think that space agencies must revisit the price and study the case again.
Many active space debris removal methods have been suggested over the last two decades. In this literature review, some of the most common space debris removal and capturing methods have been reviewed, as well as, the pros and cons have been addressed, and the up-to-date state of those methods. Moreover, it is found that many challenges are facing those proposed methods, for example, ablating a space debris with unknown physical shape and properties is still facing some technical challenges. Furthermore, it is also related to space agencies and countries policies because space exploration is a collaborative, international, and a globe wide mission.
Based on our research and observation, the Net-capturing methods are the most efficient methods, and they are at the forefront. Further on, having several methods helps viewing the issue from different points of view and uses diverse tools and equipment. Especially at this stage, the experimental stage, because most of the space debris capturing and removal methods are still under review and require deep studies and research.
Many extraordinary and fictional methods and approaches were suggested to help in the space debris mitigation process in the low orbit of earth, but through the literature review, it has been observed that any new approach, could be efficient and helpful in reducing the space junk would be considered and taken into account.
Despite all the methods suggested so far to reduce the space debris problem, there has not been a clear outcome or a system that is cost-effective and saves time. As mentioned above even if there was an efficient method, the debris will keep increasing over the next few years unless there is a progress made in the removal of space junk.
At the end, it is important that the space agencies and scientists or even researchers make a cumulative attempt to reduce the orbital debris, as the
further it proliferates, it will become more difficult to future space exploration missions. According to the papers reviewed.
The diagram shown below lists most of the space debris removal and capturing methods divided into two main categories, contact and contactless capturing methods.
Figure 3. Concept diagram of capturing methods 
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http://www.spacefuture.com/archive/orions_laser_hunting_space_debris.shtml  C. Mark and S. Kamath, “Review of Active Space Debris Removal Methods”, Space Policy, vol. 47, pp. 194-206, 2019. Available: 10.1016/j.spacepol.2018.12.005.”ARES | Orbital Debris Program Office”, Orbitaldebris.jsc.nasa.gov, 2016. [Online]. Available: https://orbitaldebris.jsc.nasa.gov/. [Accessed: 24- Feb- 2021].  C. Phipps et al., “Removing orbital debris with lasers”, Advances in Space Research, vol. 49, no. 9, pp. 1283-1300, 2012. Available: 10.1016/j.asr.2012.02.003.  D. Kessler and B. Cour-Palais, “Collision frequency of artificial satellites: The creation of a debris belt”, Journal of Geophysical Research, vol. 83, no. 6, p. 2637, 1978. Available: 10.1029/ja083ia06p02637.  T. Aadithya, “Review Paper on Orbital Debris Mitigation and Removal and A New Model Insight”, International Journal of Electrical Electronics and Data Communication, vol. 3, no. 7, 2015. Available: 10.18479/ijeedc/2015/v3i7/48263.c  R. Bessbrook, the deorbit study in the concurrent design facility, in: Presentation Handouts, Workshop on Active Space Debris Removal, vol. 17, Darmstadt, Germany, 2012.  M. Shan, J. Guo and E. Gill, “Review and comparison of active space debris capturing and removal methods”, Progress in Aerospace Sciences, vol. 80, pp. 18-32, 2016. Available: 10.1016/j.paerosci.2015.11.001.  “Robotic arm”, En.wikipedia.org, 2018. [Online]. Available:
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