MIT engineers are experimenting with a novel propulsion system that merges the speed and power of traditional chemical thrusters with the accuracy and fuel efficiency of electrical thrusters. This system could lead to the creation of more agile small satellites capable of executing both rapid maneuvers and meticulous adjustments according to mission needs. Central to this innovation is a special propellant that can energize both chemical and electrical thrusters, which typically require separate, bulky fuel supplies.<\/p>\n
“If you can have chemical and electrical propulsion in one small package, it\u2019s the best of both worlds,” says Amelia Bruno, a former postdoc from MIT’s Department of Aeronautics and Astronautics. Bruno’s study, published in the Journal of Propulsion and Power, demonstrates that a “green monopropellant” originally developed by the U.S. Air Force for chemical propulsion can also power tiny “electrospray” thrusters. These electrospray thrusters, which are small rockets using electric fields to charge liquid propellant particles, can then expel these particles into space to generate thrust.<\/p>\n
Electrospray thrusters offer significant fuel efficiency and can execute gradual and precise maneuvers needed for long interplanetary journeys. In contrast, chemical thrusters require substantial fuel to perform quick and forceful thrusts for rapid ascent, descent, or speed changes. The MIT team, having identified a propellant suitable for both thruster types, is collaborating with NASA to launch the Green Propulsion Dual Mode mission. This mission involves a briefcase-sized CubeSat equipped with a chemical thruster and four electrospray thrusters, all powered by a single propellant tank.<\/p>\n
“We could send CubeSats to Mars, or the asteroid belt, where they could make the journey slowly, using electrospray thrusters,” says co-author Paulo Lozano, the Miguel Alem\u00e1n Velasco Professor of Aeronautics and Astronautics at MIT. The mission will be the first to test a dual propulsion system for small spacecraft, potentially enabling small satellites to venture beyond Earth’s orbit.<\/p>\n
Lozano’s group at MIT creates and tests electrospray thrusters for satellites as small as a lunchbox or carry-on suitcase. These microsatellites are cheaper and easier to launch compared to traditional satellites. Electrospray thrusters, about the size of a thumbnail, sit atop small reservoirs of ionic liquid propellant. When connected to a battery, the thrusters charge and expel ions into space, generating thrust.<\/p>\n
Over the past decade, various thruster designs and ionic liquid propellants have been tested by Lozano’s team. Ionic liquids are stable and can remain liquid in space, making them ideal for this application. Bruno and Lozano have collaborated with the U.S. Air Force to test their Advanced SpaceCraft Energetic Non-Toxic propellant (ASCENT), a “green” alternative to hydrazine, traditionally used in chemical thrusters.<\/p>\n
“ASCENT happens to be an ionic liquid mixture,” Bruno says. “We thought, this should theoretically work, so we decided to investigate further.” In their study, the team tested electrospray thrusters fueled with ASCENT. Each thruster was attached to a small reservoir filled with ASCENT and placed on a MagLev stand inside a vacuum chamber to replicate space conditions.<\/p>\n
Through multiple experiments, the researchers applied varying voltage levels to activate the thrusters, causing the CubeSat to spin. They measured the thrust produced and assessed ASCENT’s fuel efficiency over continuous operation lasting up to 100 hours. ASCENT proved successful in powering electrospray thrusters, matching the performance of conventional ionic liquids.<\/p>\n
“Compared to our normal electrospray propellants, ASCENT can provide similar performance in terms of thrust,” Bruno notes. With proof that ASCENT works in both propulsion types, the team plans to test this dual system in NASA’s upcoming mission in November. This mission will mark the first use of a shared propellant tank on a satellite, offering new possibilities for both near-Earth and exploratory missions.<\/p>\n
“This will be the first time that a satellite will have a shared propellant tank,” Lozano says. Small satellites with both propulsion systems could enhance missions, such as weather and climate monitoring, by allowing flexible deployment speeds. This research receives partial support from NASA.<\/p>\n