Satellites Equipped With a Tether Would be Able to De-Orbit Themselves at the end of Their Life

There’s no denying it, we are facing an orbital debris problem! As of January 2019, the ESA’s Space Debris Office estimates that there are at least 34,000 pieces of large debris in Low Earth Orbit (LEO) – a combination of dead satellites, spent rocket stages, and other assorted bits of space junk. And with thousands of satellites scheduled to be launched in the next decade, that problem is only going to get worse.

This is a situation that cries out for solutions, especially when you consider the plans to commercialize LEO and start sending crewed missions to deep space in the coming years. A team of scientists from the Universidad Carlos III de Madrid (UC3M) has come up with a simple but elegant idea: equip future satellites with a tether system so they can de-orbit themselves at the end of their lives.

Since the beginning of the space age, countless satellites have been launched into orbit. According to the ESA’s Space Debris Office, there are at least 3,000 inactive satellites in orbit right now, along with approximately 1,950 that are still in working order. All told, it is estimated that there 8,400 metric tons of human-made material floating around in orbit.

As Gonzalo Sánchez, the coordinator of the E.T. PACK Project and a Ramón y Cajal researcher in the UC3M Bioengineering and Aerospace Engineering Department, explained:

“Space debris is one of the major challenges that the aerospace industry will have to take on in the future. These are elements that have been left in orbit as a result of human activity in space, such as the upper stages of rocket launchers and dead satellites.”

To address this, Sánchez and his colleagues came up with the Electrodynamic Tether technology for Passive Consumable-less deorbit Kit (E.T.PACK) system. This project is part of the Horizon 2020 Future and Emergent Technology (FET) program, a program spearheaded by the European Commission to foster research and innovation in science, technology, and industry.

The key to this system is a low work-function tether that consists of a strip of aluminum tape coated with a special material that allows it to emit electrons when illuminated by the Sun. This causes the tether to become attracted to Earth’s magnetic field via the Lorentz Force, effectively lowering its altitude until it burns up in Earth’s atmosphere.

The tether itself would measure 2 cm (0.8 in) in width, 50 microns in thickness, and several kilometers in length. During the launch of the satellite, the tether would be rolled up in a reel and only deployed once the satellite was in orbit. In this way, future satellites would be able to self-destruct and not become part of the space debris problem.

As Prof. Sánchez Arriaga, one of the members of the E.T.PACK development team, explained:

“It is a technology with a highly disruptive potential. A low work-function tether transform orbital energy into electrical energy while it deorbits the satellite without using any type of fuel. Unlike current propulsion systems, a low work function tether does not need propellant and uses natural resources in the space environment, such as the geomagnetic field, ionospheric plasma and solar radiation.”

One of the main challenges of the project has to do with materials science, specifically relating to the properties of the tether’s coating. “[T]he coating on the aluminum tape must have very special characteristics and an important research effort has to be done in thermionic materials, that is, those that readily emit electrons when they are heated,” added Prof. Arriaga.

When the project concludes in three years, the team hopes to have a prototype that could be used in the next phase of the project – which will involve a demonstration flight. Already, this concept has captured the interest of the ESA and industries in the NewSpace sector, and has also led to two national patents where the tether could be used for propulsion and power generation.

The E.T.PACK project, which was launched back in March, is funded by the European Commission with a budget of €3 million. The project brings together research groups and companies from three European countries, such as the Fraunhofer Institute and the Technische Universität Dresden (Germany), the University of Padova (Italy), and the Spanish companies SENER Ingeniería y Sistemas and Advanced Thermal Devices.

Further Reading: UC3M, ESA SDO