# Methodology for CubeSat Debris Collision Avoidance Based on Its Active ADCS System
## 2 State of the Art  
### Space Debris  
Space debris is any human-made object orbiting that is useless or inactive. These objects can include fragments that are orbiting Earth or re-entering the atmosphere. Debris can be a non-functional or inactive spacecraft, parts of satellites or launch vehicles, fragments of spacecraft and rockets due to explosions or collisions, debris intentionally released during spacecraft separation from its launch vehicle or during mission operations, and so on. Since the beginning of the space era, the number of objects, their combined mass, and their combined area has steadily increased, leading to the occurrence of unintentional collisions between operational payloads and space debris. The evolution of number of orbiting objects since then (October 1957) is captured in Figure 1 according to the European Space Agency (ESAC)'s Annual Space Environment Report 2022 [3]. This figure shows the object count in the last sixty years, representing the actual objects on-orbit and the cumulative objects on-orbit in case they were not removed from orbit. The data related to space debris, provided by ESA's Space Debris Office at European Space Operations Centre (ESOC), in 2022, indicate that about 12,720 satellites have been launched into orbit with the help of approximately 6180 rockets (excluding failures) whose latest states and fairings have become part of orbiting space junk [4]. It also provides some other numbers, as the number of satellites still in space is about 8060; the number of satellites still functioning is about 5400; the total mass of all space objects in Earth orbit is more than 9800 tones; the number of debris objects estimated by statistical models to be in orbit is 36,500 objects greater than 10 cm, 1,000,000 objects from greater than 1 cm to 10 cm, and 130 million objects from greater than 1 mm to 1 cm. The two worst incidents in space debris history were the intentional destruction of the Chinese anti-satellite missile test targeting the old Feng Yun-1C (FY-1C) weather satellite on 11 January 2007, and the first-ever accidental collision between two satellites, Iridium-33 and Cosmos-2251, on 10 February 2009. The first collision increased almost 20% of the entire population of catalogued human-made objects in orbit (almost 3300 fragments larger than 10 cm identified and tracked by the US Space Surveillance Network (SSN)) and the second generated the second and the fourth most important amount of space debris in space debris history [5]. The US space surveillance network (SSN) is a combination of different systems to detect, track, identify, and catalog all space debris orbiting the Earth and it is the main source of information on large space debris. Table 1 indicates the top debris contributor events by the National Aeronautics and Space Administration (NASA) [6] and this intentional breakup became the most severe orbital debris cloud in history [7]. The ranking shown in Table 1 is ordered by the number of catalogued debris, and heading this ranking is the intentional collision when China conducted its first anti-satellite missile test, destroying FY-1C with a kinetic kill vehicle. The collision happened at a particularly problematic altitude in the LEO area, as it met two criteria: first, the altitude is such that it takes many decades or longer for atmospheric drag to remove debris from orbit; second, the area is already heavily populated with operational satellites and debris resulting from previous breakups. This substantial increase in fragments poses a significant threat to operational satellites in the region, as the severity of the impact primarily depends on the orbital lifetimes of the large fragments. From microscopic particles to non-operating satellites and rocket bodies tens of meters in length, space debris can come in all sizes. When a collision occurs and space debris is  
Figure 1: Evolution of number of objects. Reprinted from ESA’s Annual Space Environment Report, 12 September 2023 [3]. created, it moves in various orbits that change over time.