Right now, 10 to 15 Rubik’s Cube-sized satellites are orbiting high above Earth. Known as cube satellites, or “CubeSats,” the devices help researchers conduct simple space observations and measure characteristics of Earth’s atmosphere. One advantage is that they are relatively cheap to deploy: While launching a rocket may cost between $50 million and $300 million, a CubeSat can “piggyback” onto a large rocket platform at an additional cost of as little as $40,000. But their small size also means they lack on-board propulsion systems, which is why they generally remain locked to a particular orbit.
Paulo Lozano, the H.N. Slater Assistant Professor of Aeronautics and Astronautics at MIT, is designing a tiny propulsion system that could allow the satellites, which weigh about a kilogram and are used for tasks that don’t require precise orbit control, to travel great distances and perform more serious tasks, such as searching for planets outside our solar system. The technology, which is based on the process of extracting and accelerating charged ions. The thruster design requires that the total volume of the propulsion system be less than 10 percent of the CubeSat.
Lozano’s design relies on electrospraying, a physics process that uses electricity to extract positive and negative ions from a liquid salt that is created in a laboratory and serves as the system’s propellant. The liquid contains no solvent, such as water, and can be charged electrically with no heat involved. Whereas other electric propulsion systems charge the ions in a chamber on the satellite, the ionic liquid in Lozano’s design has already been charged on the ground, which is why his system doesn’t need a chamber.
Electricity is then converted from the main power source of the CubeSat, typically batteries or a solar panel, and applied to a tiny structure roughly the size of a postage stamp. This thin panel is made of about 1,000 porous metal structures that resemble needles and have several grams of the ionic liquid on them. By applying voltage to the needles, an electric field is created that extracts the ions from the liquid, accelerates them at very high speeds and forces them to fly away. This process creates an ionic force strong enough to produce thrust.
The mini-thrusters are scalable, thousands of them could be built into long, thin panels to produce thrust for a much larger spacecraft that requires low, but steady, acceleration.
Lozano predicts that CubeSats using this technology will become a reality in less than three years. He plans to have a prototype of the mini-thruster in four to five months and hopes to begin testing it to measure performance metrics such as the velocity of the ions and their energy to figure out the force produced by the engine. Knowing this, researchers can estimate its efficiency.