It's hard to fit everything on a small satellite, especially the fuel, but a new propulsion system could make it easier.
Instead of having separate fuel for chemical thrusters and electrical thrusters, a Massachusetts Institute of Technology (MIT) study suggests that a single propellant can power both kinds of systems. And this idea will get an in-space test soon, if all goes according to plan.
"If you can have chemical and electrical propulsion in one small package, it's the best of both worlds," Amelia Bruno, a former postdoctoral student at MIT who led the new study, said in a university statement on Monday (June 1). "This opens the door for small satellites to do even more science, more observations, and more interesting missions, all on a smaller and cheaper platform."
The study borrows from fuel research by the U.S. Air Force, and it was partially funded by NASA. The space agency's Green Propulsion Dual Mode cubesat spacecraft will launch no earlier than November to see if the propulsion system and monopropellant, already tested on the ground, also works well in space.
The mission to low Earth-orbit will serve as a valuable demo, the agency stated, for missions that go much farther from our planet — to places such as Mars, the eventual destination for human missions under NASA policy.
"NASA is looking to expand deeper into space to support future agency objectives. Major drivers for these activities include researching and developing new and advanced propulsion systems and capabilities," agency officials wrote of the cubesat mission, which last year was expected to launch in October 2025, according to a SpaceNews report.
The green monopropellant the mission is using, tested in a new MIT study in the Journal of Propulsion and Power, builds upon previous Air Force research. The propellant is called ASCENT, or Advanced Spacecraft Energetic Non-Toxic Propellant. The fuel is marketed as greener, or less toxic, than the usual high-efficiency hydrazine that is perfect for making big maneuvers in space but is dangerous to handle. It's also been tested in space before, during NASA's Green Propellant Infusion Mission in 2019-20 (when the fuel was called AF-M315E; it has since been renamed, according to the Air Force Research Laboratory, which developed it).
What's more, ASCENT — despite being originally envisioned for chemical thrusters that use fuel quickly, during big space moves like orbital insertions — may also be suitable for electrospray thrusters. These thrusters are designed to make smaller, long-term adjustments to a spacecraft's trajectory. The tiny (thumbnail- to dime-sized) thrusters use an electric field to accelerate particles of liquid propellant. The acceleration fires the propellant into space as a spray (hence the name).
The new MIT study appears to show that one fuel could serve different spacecraft needs. Engineers tested how well electrospray thrusters on the ground performed with ASCENT, using a model cubesat set on a testbed that magnetically suspended a device in a vacuum chamber, simulating the free-floating environment of space. The team tried out different voltage levels on the thrusters and examined the spray's ability to maneuver and spin the cubesat.
"Compared to our normal electrospray propellants, ASCENT can provide similar performance in terms of thrust," Bruno said. "Now that we know our thrusters work with ASCENT, we can start thinking of all the ways we can make them even better."
While NASA's focus is on distant destinations, ASCENT could also be repurposed for missions closer to home. Small satellites, for example, could make use of the propellant to save fuel during Earth-observing missions, especially when they're tasked to pivot for a fast-moving weather event.
"Say there's a storm coming, and you'd want to deploy your constellation of small satellites to observe over one location," study co-author Paulo Lozano, director of MIT's space propulsion laboratory, said in the same statement. "You could choose to send them quickly, or slowly, depending on the nature of the observation. And the only way to do that is if you have two propulsion systems, which is now possible."
