# Methodology for CubeSat Debris Collision Avoidance Based on Its Active ADCS System
## 2 State of the Art
### CubeSats and Space Debris  
Since their inception, CubeSats have proven to be a game-changer in the space industry. Due to their small size and low cost, they have opened up access to space to a wide range of groups. Initially intended to promote satellite development programs for educational institutions for research and training purposes, they have been adopted for science missions, small startups, technology demo flights, commercial applications, and even individual hobbyists. CubeSats are not only easy to build and launch, but they can also be customized to meet the specific needs of different missions. In 1999, the CubeSat standard was created at California Polytechnic State University (Cal Poly) with the primary goal of making space exploration more accessible and affordable for university researchers. The CubeSat Design Specification (CDS) REV 14.1 [15] standard provides guidelines on the design of CubeSats, including their dimensions, mass, power requirements, communication interfaces, and potentially hazardous materials. Figure 2: Example of timeline of collision avoidance operational activities [14]. Any satellite with a weight below 10 kg is classified as a nanosatellite. CubeSats adhere to standardized dimensions known as \"Units\" or \"U\", which measure 10 cm \(\times\) 10 cm \(\times\) 10 cm. These small satellites are available in six sizes: 1U, 1.5U, 2U, 3U, 6U, and 12U, and their weight is usually less than 2 kg per U [15]. Figure 3 shows the current CubeSat family as it is defined in the CDS. 1U, 1.5U, 2U, and 3U CubeSats have a base of 10 cm \(\times\) 10 cm, changing the height to complete the number of units. For example, 6U CubeSats have a base of 10 cm \(\times\) 20 cm and 12U CubeSats have a base of 20 cm \(\times\) 20 cm, and both have the height of a 3U. In addition to their versatility, CubeSats are also an ideal platform for testing new technologies and conducting scientific research in space. Many CubeSat missions have focused on Earth observation, remote sensing, and communication experiments, while others have studied the behavior of microorganisms in microgravity or tested new propulsion systems. In fact, the early versions of the CDS actually prohibited propulsion. That requirement has been eased, leading to many more complex missions that demand propulsion. As the CubeSat industry continues to grow, more advanced capabilities are being added to these tiny spacecrafts, such as on-board computers, propulsion systems, and robotic arms. With their low cost and flexible design, CubeSats are poised to play an increasingly important role in space exploration and research in the years to come. There are some facts about Nanosats (2023) [16], such as the number of Nanosats launched is 2138; the number of Cubesats launched is 1960; the Interplanetary CubeSats is 15; the number of NanoSats destroyed on launch is 115; the number of countries with NanoSats is 80; the forecast of NanoSats to launch in the next 6 years is 2080. The limited orbital lifetime of CubeSats is a challenge that requires careful mission planning and monitoring. These satellites typically operate at low altitudes and have a high area-to-mass ratio, which makes them prone to atmospheric drag and orbital decay. As a result, their orbital lifetime is often limited to a few months to a few years. However, CubeSats are not only difficult to track but also pose a potential collision risk to other satellites in orbit. Due to their small size and frequent lack of propulsion systems (due to the mass and cost increment), they cannot perform collision avoidance maneuvers, making it crucial to detect and avoid any potential collisions in advance. Despite these challenges, CubeSats have been designed with various advanced systems to enhance their functionality and effectiveness in low Earth orbit. Many CubeSats incorporate ADCS systems, and/or reaction wheels based on magnetorquer actuators, which enable them to maintain their orientation and stabilize their position in space.