6.1 International debris mitigation guidelines (IADC, UN)

Space debris mitigation guidelines are crucial for ensuring sustainable space activities. International organizations like IADC and UN COPUOS have developed key guidelines to limit debris generation and promote responsible space operations.

These guidelines cover post-mission disposal, including the 25-year rule and passivation, as well as operational measures like collision avoidance and debris monitoring. They aim to reduce risks and preserve the space environment for future use.

International Organizations and Guidelines

Inter-Agency Space Debris Coordination Committee (IADC)

• IADC is an international forum of space agencies that coordinates activities related to human-made and natural debris in space
• Founded in 1993, it consists of 13 member agencies including NASA, ESA, JAXA, and Roscosmos
• Aims to exchange information on space debris research activities between member agencies, facilitate opportunities for cooperation, and identify debris mitigation options
• Develops and publishes guidelines for the mitigation of space debris, which have been used as the foundation for space debris mitigation standards adopted by other organizations (UN COPUOS)

United Nations Committee on the Peaceful Uses of Outer Space (COPUOS)

• COPUOS is a committee within the United Nations that governs the exploration and use of space for the benefit of all humanity
• Established in 1959 to review international cooperation in peaceful uses of outer space, encourage space research programs, and study legal problems arising from the exploration of outer space
• Consists of 95 member states and is the primary international forum for the development of laws and principles governing space-related activities
• In 2007, COPUOS adopted the Space Debris Mitigation Guidelines, which are based on the IADC guidelines and provide a framework for space debris mitigation measures to be implemented by individual countries and international organizations

Space Debris Mitigation Guidelines

• A set of internationally recognized guidelines for the mitigation of space debris, developed by the IADC and adopted by the UN COPUOS
• Aim to limit the generation of space debris in the near-Earth environment by promoting responsible space operations and design practices
• Key measures include limiting debris released during normal operations, minimizing the potential for on-orbit breakups, post-mission disposal, and prevention of on-orbit collisions
• Guidelines are voluntary and non-binding, but have been widely adopted by space agencies and satellite operators worldwide as a standard for mitigating space debris

Post-Mission Disposal

25-year rule

• Guideline stating that spacecraft and orbital stages should be designed to ensure their post-mission orbital lifetime is less than 25 years
• Aims to limit the long-term presence of non-functional objects in low Earth orbit (LEO) and reduce the risk of collisions with active satellites
• Achieved through various methods such as propulsive maneuvers, drag enhancement devices, or disposal orbits
• Applies to objects in LEO, as objects in higher orbits (MEO, GEO) have much longer orbital lifetimes and require different disposal strategies

Passivation

• The process of removing stored energy from a spacecraft or orbital stage at the end of its mission to reduce the risk of explosive breakup
• Involves depleting propellants, discharging batteries, and venting pressurized systems
• Helps prevent the creation of new debris fragments due to accidental explosions of defunct spacecraft
• Required by most space debris mitigation guidelines and is considered a critical step in the post-mission disposal process

Orbital lifetime reduction

• Techniques used to reduce the time a spacecraft or orbital stage remains in orbit after the end of its mission
• Includes methods such as lowering the orbit to accelerate atmospheric drag decay, using propulsive maneuvers to move the object to a disposal orbit, or deploying drag enhancement devices (balloons, sails)
• Aim is to comply with the 25-year rule and minimize the long-term presence of debris in heavily used orbital regions
• Choice of method depends on factors such as the object's size, orbit, and available on-board resources (propellant, power)

Re-entry risk

• The potential for a spacecraft or orbital stage to cause damage or injury during its uncontrolled re-entry into Earth's atmosphere
• Determined by factors such as the object's size, material composition, and re-entry trajectory
• Space debris mitigation guidelines require that the risk of human casualty from re-entering debris be less than 1 in 10,000
• Controlled re-entries, where the object's trajectory and impact location can be predicted, are preferred for large or high-risk objects to minimize potential damage on the ground

Operational Mitigation Measures

Collision avoidance

• The process of monitoring the trajectories of space objects and maneuvering active spacecraft to avoid potential collisions
• Involves using ground-based and space-based surveillance networks to track objects and predict close approaches (conjunctions)
• When a high-risk conjunction is identified, satellite operators can perform collision avoidance maneuvers to adjust the spacecraft's orbit and reduce the probability of a collision
• Requires accurate orbital data, timely conjunction assessments, and efficient decision-making processes to be effective in preventing collisions and the creation of new debris

Orbital debris monitoring

• The continuous observation and tracking of space debris to maintain situational awareness and support collision avoidance activities
• Conducted using a combination of ground-based radar, optical telescopes, and space-based sensors
• Provides data on the size, shape, orbit, and material composition of debris objects, which is used to characterize the debris environment and assess collision risks
• Major debris monitoring systems include the U.S. Space Surveillance Network (SSN), the European Space Surveillance and Tracking (EU SST) program, and the Inter-Agency Space Debris Coordination Committee (IADC) observation campaigns

Spacecraft shielding

• The use of protective materials and structures to reduce the damage caused by impacts with small debris objects
• Includes Whipple shields (thin outer bumper and spaced rear wall), multi-shock shields, and advanced materials such as Kevlar and ceramic composites
• Designed to break up and disperse the impacting debris, reducing the penetration depth and damage to the spacecraft's critical components
• Effective against small debris (millimeter to centimeter-sized) but cannot protect against impacts with larger objects, which require collision avoidance measures

Redundancy systems

• The incorporation of backup components and subsystems in spacecraft design to maintain functionality in the event of a debris impact or other failure
• Includes redundant power supplies, communication systems, on-board computers, and control actuators
• Allows the spacecraft to continue its mission even if some components are damaged or lost due to debris impacts
• Increases the overall reliability and resilience of the spacecraft, reducing the risk of mission failure and the creation of new debris from on-orbit breakups