The European Space Agency is testing a prototype thruster capable of using the molecules of the residual atmosphere, 125 miles above sea level, to propel satellites. A virtually inexhaustible fuel.
It would be a “world first”, says the European Space Agency (ESA) on its website. As part of its technological research program, the Italian company Sitael has developed an ion thruster capable of using residual air from the upper atmosphere as fuel. A virtually inexhaustible source that could power satellites in low orbit for many years. Applications in the field of Earth observation or for solar system exploration missions are potentially very important.
For example, ESA’s GOCE satellite, which was designed to study the Earth’s gravity field, was flying at an altitude of 250 km. To compensate for the friction of the air and to raise its orbit from time to time, it used a “classical” ion thruster . This type of thruster uses solar energy to create ions (electrically charged atoms) and accelerate them, which gives it its thrust. The satellite must nevertheless supply the gas to be ionized, in this case xenon. GOCE had carried 40 kg of xenon on board. Once these reserves were exhausted, after five years, the mission was interrupted in 2013. If atmospheric air was used, the mission could have lasted many more years!
Accelerated oxygen and nitrogen
Working with residual atmospheric air is complex for several reasons. Oxygen and nitrogen atoms are lighter and more difficult to ionize than xenon, so they offer lower thrust for higher electrical costs. In addition, a satellite travels at more than 17,000 mph at this type of altitude. Air molecules tend to bounce rather than compress in the collector. Engineers were therefore forced to develop a special design and a more efficient electric “ignition” system.
The new machine was tested in a vacuum chamber. First with a stream of xenon. Then with a xenon-air mixture. “When the engine exhaust plume changed from the characteristic blue of xenon to purple, we knew we had succeeded,” says Louis Walpot of ESA.
“We finally relighted the system several times with only atmospheric fuel to demonstrate the feasibility of the concept,” said Louis Walpot. The air was not very dense and sent at very high speed to simulate the conditions encountered by a satellite flying at more than 125 miles of altitude. “This result shows that electric propulsion using air is no longer in the realm of theory, but that it is indeed a tangible operational concept, ready to be developed and that can one day be used to define missions of a new kind,,” he added.