At MIT's Space Propulsion Laboratory, engineers have solved one of small-satellite design's trickiest puzzles: how to fit two completely different types of rocket engines—chemical and electrical—into a single, fuel-efficient package no bigger than a briefcase.
The innovation matters because small satellites, or CubeSats, have transformed what's possible in space exploration. These microsatellites cost far less to launch than conventional spacecraft and can observe Earth, conduct scientific experiments, and even venture beyond our planet. But their size has always come with a fundamental constraint: they can't easily do both what traditional rockets do—fast, powerful bursts—and what delicate electrical thrusters do—slow, precise adjustments over long distances. Until now, engineers had to choose one capability or the other, and compromise.
MIT researchers, led by Amelia Bruno and Paulo Lozano, have demonstrated that a single propellant called ASCENT—Advanced SpaceCraft Energetic Non-Toxic propellant, originally developed by the U.S. Air Force—can power both chemical and electrospray thrusters. Their findings, published in the Journal of Propulsion and Power, upend that either-or choice. "If you can have chemical and electrical propulsion in one small package, it's the best of both worlds," says Bruno, a former postdoc in MIT's Department of Aeronautics and Astronautics.
Electrospray thrusters, which are about the size of a thumbnail, work by using electric fields to charge particles in an ionic liquid propellant and shoot them into space as a fine mist. They're extraordinarily fuel-efficient and excel at making slow, careful maneuvers—the kind needed to navigate an interplanetary journey. Chemical thrusters, by contrast, burn through fuel quickly but deliver the raw power needed for rapid acceleration and deceleration. The ASCENT propellant, an ionic liquid made from salts that remain stable even in space, can fuel both systems from a single tank.
The real-world test is already underway. MIT is working with NASA on the Green Propulsion Dual Mode mission, a briefcase-sized CubeSat that will carry one chemical thruster and four electrospray thrusters, all drawing from a single propellant tank. This marks the first time a small spacecraft will fly with such a dual-mode system, and if successful, it could unlock entirely new possibilities for deep-space exploration.
Paulo Lozano, the Miguel Alemán Velasco Professor of Aeronautics and Astronautics, imagines the practical payoff: "We could send CubeSats to Mars, or the asteroid belt, where they could make the journey slowly, using electrospray thrusters. You could then use your chemical thrusters to quickly move to look at interesting features. You could have a lot more flexibility to do a lot more things."
The chemistry behind it is elegant. Ionic liquids—essentially liquid salts—possess a rare property: they remain stable and liquid in the harsh environment of space, where most fuels would freeze or boil away. When connected to a battery, the liquid becomes a sea of charged particles ready to be pulled into an electrospray, or burned in a traditional chemical reaction. By finding a single propellant that excels at both, MIT's team has removed a major constraint on small-satellite design.
If the upcoming NASA mission succeeds, miniaturized spacecraft will no longer have to trade precision for power. That flexibility could transform what small satellites can achieve, from detailed planetary surveys to audacious missions to distant asteroids—all on platforms cheaper and nimbler than ever before.