De-orbiting is the controlled descent and re-entry of satellites into Earth’s atmosphere. Methods include propulsion systems and solar sails. Satellites and makers face problems such as legalities and space junk potential.
De-orbiting is intended to reduce space debris and protect safety of other satellites and future missions. The process maneuvers a satellite from its operational orbit into a trajectory leading back to Earth.
Without proper de-orbiting, satellites can become space debris. Space junk is a growing problem. According to the European Space Agency over 36,000 pieces of debris larger than 10 cm currently orbit Earth.
Methods to De-orbit Satellites
De-orbiting is a carefully executed event designed to remove a satellite from orbit and into the Earth's atmosphere. The goal of de-orbiting is to ensure the satellite burns up upon re-entry or lands in a designated area.
Controlled Re-entry
This is the most precise and preferred method. Onboard propulsion systems or thrusters carefully lower the satellite's orbit, targeting a specific re-entry point.
This is usually over a remote area of the ocean. The South Pacific Ocean Uninhabited Area (SPOUA) is also known as the "spacecraft cemetery."
Controlled re-entry systems may involve parachutes or heat shields to guide the descent. This hopes to ensure fragments land in regions uninhabited by people.
For instance NASA's decommissioned Upper Atmosphere Research Satellite is dumped into the ocean after controlled re-entry in 2011. It can add to debris like the 11 million tons of plastic entering the ocean annually.
Atmospheric Drag Augmentation
For satellites lacking sufficient onboard propulsion, drag augmentation devices like inflatable balloons or large sails can be deployed. These devices increase surface area and atmospheric drag to accelerate descent.
This method relies on the natural slowing effect of the Earth's atmosphere at lower altitudes. Solar sails use solar radiation pressure to create drag. By deploying a large reflective surface, satellites slow their orbits gradually.
For example, experiments with solar sails indicate that they may reduce a satellite's orbital decay time by 30-50%, eventually leading to re-entry into the atmosphere.
These absorb and convert sunlight to create energy and propel the spacecraft forward. The LightSail 2 mission by The Planetary Society uses solar sails for power.
Propulsion System
Most satellites have propulsion systems for orbit adjustments. When de-orbiting, these systems activate to slow the satellite down, enabling it to descend into the atmosphere.
The propulsion system on many satellites can use chemical fuel to decrease speed by up to 10%, causing them to re-enter Earth’s atmosphere. There, the heat generated by friction makes them burn up.
Disintegration of satellites in the atmosphere at the end of their lives may minimize the amount of space debris. This process however releases satellite ash into the Earth's middle atmospheric layers.
This metallic ash can damage the atmosphere and affect the climate. With more space creations burning up daily, atmospheric ash accumulation is an environmental concern.
Tethers
Electrodynamic tethers (EDTs) are long cables extended from the satellite. They interact with Earth’s magnetic field to create drag.
Electrodynamic tethers work on electromagnetic principles. They can act as generators by transforming kinetic energy into electrical energy, or as motors by converting electrical energy into kinetic energy.
In a tether propulsion system, craft can use long, strong conductors to change the spacecraft orbits. When direct current is applied to the tether, it exerts a Lorentz force against the magnetic field.
The tether then exerts force on the vessel. It either accelerate or brake an orbiting spacecraft. Space tethers have been deployed in space missions, and are used for testing and research.
Ground Control
Ground teams monitor the satellite's position, calculate maneuvers, and send commands. Ground-based radar and optical telescopes track satellites and debris, providing data for de-orbit planning.
Mission End-of-Life (EOL) Planning: This involves designing spacecraft with features that facilitate de-orbiting, such as:
Sufficient Propellant: So enough fuel is available at end of mission for a controlled de-orbit maneuver.
Passive De-orbit Mechanisms: Integrating systems to automatically trigger de-orbiting without requiring active control, like inflatable drag sails.
Design for Demise: Selecting materials and designing the spacecraft to maximize its chances of completely burning up during re-entry.
A space object usually has to weigh over 1000 kg (1 ton) to partially survive re-entry. That's about as heavy as a rhinoceros, and includes abandoned satellites, space stations and rocket bodies.
Of these, only small fragments are likely to hit the ground. NASA catalogues an average of piece of debris returning to Earth daily over the past 50 years.
Successful De-orbits
Numerous satellites from various space agencies have been strategically brought down to Earth through controlled re-entry.
The European Space Agency's (ESA) Aeolus wind observation satellite uses assisted re-entry techniques to steer satellites back to Earth when needed. The intentional de-orbiting of the Envisat satellite in 2012 is one example.
India's RESOURCESAT-1, launched in 2003 and decommissioned in 2018, is a successful de-orbit as its propulsion system guides it through controlled re-entry. It's considered to completely burn up upon entering the atmosphere, leaving no obvious debris.
Starlink Satellites: Each Starlink satellite is programmed to re-enter the Earth's atmosphere at the end of its operational life, where it flamboyantly burns up. This happens at a rate of four to five a day.
7,821 Starlinks are thus far launched. 817 are retired to reentry, including some which failed at birth. In the month of January 2025, 120 Starlink satellites re-entered Earth's atmosphere.
New Rules for Satellite Launches After September 2024
Growing concerns about space debris have led to stricter regulations. From September 2024, many space agencies require every new satellite to have a de-orbit plan within five years of the end of its mission.
This hopes to clear low Earth orbit more quickly and reduce accumulation of debris. Violators are refused launch permission.
Before Sept 2024 satellites were required to de-orbit within 25 years of the end of mission. Satellites further from Earth are often sent deeper into space as a way of disposal, another space junk mitigation challenge.
Problems Faced in Satellite De-orbit
Cost: Retrofitting existing satellites with de-orbiting capabilities is expensive, and even designing it into new satellites adds to the overall mission cost.
Technical Complexity: Executing precise de-orbit maneuvers requires sophisticated control systems, accurate tracking data, and reliable propulsion.
Propellant Limitations: Many older satellites lack sufficient propellant to perform a controlled re-entry, forcing reliance on less predictable methods like atmospheric drag.
About 40% of satellites in orbit have propulsion systems over 15 years old. The equipment might not work as desired during de-orbit phases.
Satellite Failures: If a satellite fails before its planned de-orbit, it becomes an uncontrolled object in space, potentially colliding with other satellites or spacecraft.
Space Law and Regulations: Enforcing de-orbiting regulations on all satellite operators needs international cooperation.
Orbital Debris: Existing debris in orbit complicates de-orbiting. Risk of collision with space debris during re-entry is as high as 10%. Space debris includes defunct satellites, rocket bodies, and fragments from collisions.
Technical Limitations: De-orbiting larger satellites, such as the International Space Station (ISS), is complex due to their size and high velocity. The ISS is scheduled for termination in 2030.
Personnel need to do precise calculations, requiring resources and time. Planned de-orbit of the ISS could take over a year of preparation.
Financial Constraints: Implementing effective de-orbiting strategies can be daunting for smaller organizations or private companies. Budgets can restrict access to advanced technologies or safeguards.
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