In the realm of space operations, the deorbiting of satellites is an increasingly important consideration. As the number of satellites in orbit grows, so does the need for effective strategies to safely remove them from orbit at the end of their operational life. This is important to mitigate the risks of space debris, which can pose a significant threat to both manned and unmanned space missions.
The Growing Concern of Space Debris
Space debris, commonly known as “space junk,” comprises a variety of objects, including defunct satellites, spent rocket stages, and fragments from disintegration, erosion, and collisions. According to the European Space Agency (ESA), there are about 34,000 objects larger than 10 cm, 900,000 objects from 1 cm to 10 cm, and 128 million objects from 1 mm to 1 cm in orbit around Earth. These objects travel at extremely high velocities and can cause severe damage to functional spacecraft and satellites.
Key Deorbiting Strategies
Controlled Re-Entry
- Atmospheric Burn-Up: This strategy involves lowering the satellite’s orbit to ensure that it re-enters the Earth’s atmosphere and burns up. This method is often used for smaller satellites and requires careful calculation to ensure re-entry over uninhabited areas, like vast ocean expanses, to minimize the risk of debris causing damage on the ground.
- Targeted Deorbit: Larger satellites and space stations (like the Mir space station deorbited in 2001) are brought down in a controlled manner. This process involves firing the satellite’s thrusters to precisely control its descent, aiming for a safe re-entry point.
Passive Deorbiting Systems
- Drag Sails: Satellites can be equipped with deployable drag sails that increase the spacecraft’s surface area, thereby enhancing atmospheric drag. This drag accelerates orbital decay, naturally pulling the satellite towards the Earth’s atmosphere for burn-up.
- Electrodynamic Tethers: These are long conducting tethers attached to the satellite. When deployed, they interact with the Earth’s magnetic field, generating electric currents that create a drag force, leading to a gradual decrease in altitude.
Active Deorbiting Systems
- On-board Propulsion: Some satellites are equipped with their own propulsion systems, which can be used at the end of their life to either lower their orbit for atmospheric re-entry or boost them to a “graveyard orbit” – a higher orbit where they are less likely to interfere with operational satellites.
- External Vehicle Assistance: This involves the use of a secondary vehicle or space tug, which docks with the satellite and maneuvers it into a deorbit trajectory or to a graveyard orbit. This strategy is particularly relevant for larger satellites that do not have sufficient fuel or capability to deorbit themselves.
The Role of International Regulations and Best Practices
The mitigation of space debris and the safe deorbiting of satellites is a matter of international concern. Several international guidelines and best practices have been established to address this issue:
- UN Guidelines for the Long-term Sustainability of Outer Space Activities: These guidelines encourage states to consider the long-term sustainability of space activities, including the safe deorbiting of satellites and space debris mitigation.
- Inter-Agency Space Debris Coordination Committee (IADC) Guidelines: The IADC, comprising space agencies from 13 countries, has developed guidelines that recommend, among other things, limiting the long-term presence of spacecraft in low Earth orbit (LEO) after the end of their missions.
- National Regulations: Many countries have developed their own regulations and guidelines. For example, the United States Federal Communications Commission (FCC) requires satellite operators to deorbit their satellites within 5 years of mission completion.
Summary
The effective deorbiting of satellites is essential to maintain the long-term sustainability of space activities. As technological advancements continue, the development and implementation of efficient deorbiting strategies will be critical in addressing the challenges posed by space debris. Collaboration among international space agencies, adherence to guidelines, and innovations in deorbiting technologies are crucial in ensuring the continued safe and responsible use of outer space.
