🛰️Space Debris Mitigation Unit 8 – Active Debris Removal Technologies

Key Concepts and Definitions

• Active Debris Removal (ADR) involves actively removing space debris from orbit using various technologies and methods
• Space debris includes non-functional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris
• Kessler Syndrome describes a theoretical scenario where the density of objects in low Earth orbit (LEO) becomes high enough that collisions between objects could cause a cascade, increasing the likelihood of further collisions
  • This could render space activities and the use of satellites in specific orbital ranges unfeasible for many generations
• Deorbiting is the process of removing a spacecraft or piece of debris from orbit by causing it to re-enter Earth's atmosphere and burn up or fall into the ocean
• Post-mission disposal (PMD) is a debris mitigation strategy that involves removing a spacecraft from orbit at the end of its operational life to prevent it from becoming a source of debris

Historical Context and Current Challenges

• The space debris problem has been growing since the beginning of the space age in the 1950s
• As of January 2021, the United States Space Surveillance Network tracked more than 27,000 pieces of orbital debris
  • This includes only objects larger than about 10 cm in low Earth orbit and 1 m at geostationary altitudes
• Collisions between space objects have already occurred, such as the 2009 collision between the operational Iridium 33 satellite and the defunct Kosmos-2251 satellite
• Current challenges include the lack of international agreements on debris removal, the high cost of ADR missions, and the technical difficulties associated with removing small, fast-moving objects from orbit
• The increasing number of satellite constellations, such as SpaceX's Starlink and Amazon's Project Kuiper, could exacerbate the space debris problem if not properly managed

Types of Active Debris Removal Technologies

• Robotic arms can be used to capture and remove debris from orbit
  • These arms can be equipped with grippers, nets, or harpoons to secure the debris
• Tethers can be used to connect a spacecraft to a piece of debris, allowing the spacecraft to deorbit the debris by slowing down and causing both objects to re-enter Earth's atmosphere
• Nets can be deployed to capture debris and then be used to deorbit the captured objects
• Lasers can be used to ablate the surface of debris objects, creating a small thrust that can be used to deorbit the object over time
• Ion beams can be directed at debris objects to create a plasma plume that generates a small thrust, gradually altering the object's orbit and causing it to re-enter Earth's atmosphere

Operational Principles and Mechanisms

• ADR technologies must be able to rendezvous with and capture debris objects moving at high speeds in orbit
• Robotic arms and grippers must be able to securely attach to debris objects of various shapes and sizes
  • This requires advanced sensors, control systems, and machine vision algorithms
• Tethers must be strong enough to withstand the forces generated during the deorbiting process and must be able to be deployed and retracted reliably
• Nets must be designed to deploy and capture debris objects without creating additional debris in the process
• Laser and ion beam systems must be able to accurately target debris objects and generate sufficient thrust to deorbit them over time
  • This requires high-precision pointing and tracking systems, as well as advanced power and thermal management technologies

Case Studies and Missions

• The RemoveDEBRIS mission, led by the University of Surrey and launched in 2018, successfully demonstrated key ADR technologies, including a net capture system and a harpoon capture system
• The CleanSpace One mission, proposed by the Swiss Space Center, aims to use a robotic arm to capture and deorbit small debris objects
• The ESA's e.Deorbit mission, currently in the study phase, plans to use a robotic arm to capture and deorbit a large, defunct satellite
• JAXA's Commercial Removal of Debris Demonstration (CRD2) mission, planned for launch in 2023, will test an electrodynamic tether system for deorbiting debris
• Astroscale's ELSA-d mission, launched in 2021, is demonstrating the use of a magnetic docking system for capturing and deorbiting debris

Technical Limitations and Challenges

• Capturing and deorbiting debris objects is technically challenging due to their high speeds, small sizes, and unpredictable tumbling motions
• ADR technologies must be able to operate reliably in the harsh space environment, including exposure to extreme temperatures, radiation, and vacuum conditions
• The cost of developing and launching ADR missions is currently high, which may limit their widespread adoption
  • Estimates for the cost of removing a single large debris object range from tens of millions to hundreds of millions of dollars
• ADR technologies must be designed to minimize the risk of creating additional debris during the removal process
• The limited payload capacity of current launch vehicles restricts the size and complexity of ADR systems that can be deployed

Legal and Ethical Considerations

• There is currently no international legal framework governing the removal of space debris, which could lead to disputes over ownership and liability
• ADR missions must comply with existing space law treaties, such as the Outer Space Treaty and the Liability Convention
  • These treaties establish basic principles, such as the prohibition of claiming sovereignty over celestial bodies and the liability of launching states for damage caused by their space objects
• The removal of debris objects without the consent of the launching state could be considered a violation of national sovereignty
• ADR technologies could potentially be used for military purposes, such as disabling or destroying active satellites, raising concerns about the weaponization of space
• The cost of ADR missions raises questions about who should bear the financial responsibility for cleaning up space debris

Future Developments and Research

• Advances in robotics, artificial intelligence, and materials science could lead to the development of more sophisticated and efficient ADR technologies
• The use of in-orbit servicing spacecraft, capable of refueling, repairing, and upgrading satellites, could help reduce the generation of new debris
• The development of international guidelines and standards for the design and operation of spacecraft could help minimize the creation of new debris
  • This includes the adoption of post-mission disposal strategies and the use of materials that are less likely to generate debris upon impact
• Research into the long-term effects of space debris on the space environment and the Earth's atmosphere could help inform future debris mitigation strategies
• The establishment of an international fund or mechanism for financing ADR missions could help overcome the current economic barriers to debris removal and encourage global cooperation in addressing the space debris problem