The European Space Agency (ESA) has developed the world's first electric thruster that can collect air molecules from the top of the atmosphere and use them as a propellant. This technological development will allow satellites to operate for longer in very low-Earth orbit.
Electric thrusters use electric fields to accelerate charged particles (usually ions) out of the spacecraft. The craft carries its own propellant and slowly releases it over time. The new design allows for the collection of propellant directly from the atmosphere making satellites lighter and reducing the cost of the mission.
“This project began with a novel design to scoop up air molecules as propellant from the top of Earth’s atmosphere at around 200-kilometer (124-mile) altitude with a typical speed of 7.8 kilometers (4.8 miles) per second,” ESA’s Louis Walpot said in a statement. “This result means air-breathing electric propulsion is no longer simply a theory but a tangible, working concept, ready to be developed, to serve one day as the basis of a new class of missions.”
The system is surprisingly simple. It has no valve or complex parts and simply uses the oncoming high-speed molecules a satellite would naturally encounter. The challenge was to make sure the particles would be collected and compressed to be used by the thruster instead of bouncing off the craft and slowing it down.
Researchers ran simulations of the expected behavior of particles around the spacecraft and quickly began to test the most plausible scenarios experimentally. The collecting system was designed in Poland, with the dual-stage electric thruster was developed in Italy.
“Instead of simply measuring the resulting density at the collector to check the intake design, we decided to attach an electric thruster," explained Walpot. "In this way, we proved that we could indeed collect and compress the air molecules to a level where thruster ignition could take place, and measure the actual thrust.”
The team first used xenon to test the system, as the noble gas is a common propellant for these types of propulsion systems. They then substituted it with a nitrogen-oxygen mixture to understand the behavior of the thruster when fed the “atmospheric propellant”.
“When the xenon-based blue colour of the engine plume changed to purple, we knew we’d succeeded,” Walpot added.
The project will certainly be important for low-Earth orbit but it might also be used in future planetary missions around other objects in the Solar System. Currently, over 200 craft are electrically propelled.