3D PRINTING AMONG THE STARS
A modular, 3D-printed electrospray engine has a game-changing goal: to manufacture or repair spacecraft propulsion systems directly in space.
Written by Nicole Imeson
A MAJOR DISADVANTAGE of space flight and research is the fact that there aren’t any production facility pit stops that can make a part if something breaks after leaving Earth’s orbit. While resupply missions have been the answer, now, Massachusetts Institute of Technology (MIT) researchers have designed a modular, 3D-printed electrospray engine that could instead manufacture or repair spacecraft propulsion systems directly in space.
This innovation would provide greater mission resilience and sustainability, especially in locations where supply refills remain difficult.
What’s more, the team also uncovered an unexpected breakthrough during testing: voltage can modulate thrust in electrospray engines.
For years, engineers used voltage in electrospray engines operating in cone-jet mode like an on-switch—just enough to start the process. Once the engine activated, they shifted focus to adjusting current and propellant flow rate, leaving voltage unchanged. The MIT team’s discovery that voltage can also modulate thrust defies long-held assumptions.
“People thought of voltage as only the trigger. But we found you can vary the voltage itself to throttle thrust. There’s more control there than we realized,” explained Luis Fernando Velásquez-García, principal research scientist at MIT’s Research Laboratory of Electronics and Microsystems Technology Laboratories.
“You could 3D-print the hardware in orbit. Or if a module stopped working, you could swap it with a freshly printed one.”
—Luis Fernando Velasquez-Garcia, MIT
ADDITIVE MANUFACTURING
To ensure each emitter received uniform propellant flow, the research team used two-photon polymerization (2PP) 3D additive printing. This high-resolution technique uses a laser to harden a photosensitive liquid resin. The resin solidifies only where the laser is focused, since the material requires two photons to collide at a precise point to trigger polymerization. By guiding the laser—like a light pen—through the resin, they built structures point by point, layer by layer. This method created ultra-fine features like microchannels for fluid or complex scaffolds, all smaller than a human hair.
“The emitter module alone took three to four hours to print using 2PP. But printing the whole electrospray engine that way would’ve taken several days and we didn’t need that level of detail for every part. So, we made it modular. We printed the high-resolution parts with 2PP and the larger structure using digital light processing (DLP),” explained Hyeonseok Kim, a doctoral candidate at MIT focused on nanosatellite manufacturing.
Unlike 2PP’s pinpoint laser, DLP uses a projector to flash entire patterns of UV light onto a resin pool. Wherever light touches, the resin instantly hardens. The machine then adjusts the build platform and projects the next image, hardening another layer, building objects slice by slice in a matter of hours. Using this hybrid approach, researchers printed the remaining modules with DLP in just two to three hours, balancing precision and speed.
Vacuum conditions, extreme temperatures, microgravity, and the high cost of transporting materials from Earth are among the challenges that have limited building and repair work in space. Additive manufacturing would allow astronauts to 3D-print and swap out parts, or entire systems, on demand, reducing dependence on resupply missions from Earth. Modular designs would simplify maintenance by enabling quick replacement of failed components with printed substitutes, eliminating the need to carry bulk spare inventories.
“You could 3D-print the hardware in orbit. Or if a module stopped working, you could swap it with a freshly printed one,” explained Velásquez-García.
This fully 3D-printed, droplet-emitting electrospray engine would enable small satellites to make in-orbit maneuvers and can be produced for a fraction of the cost of traditional thrusters. The device features a complex hydraulic system to store and regulate the flow of liquid, efficiently shuttling propellant through microfluidic channels to a series of emitters. Images: Hyeonseok Kim
A NEW EDGE
Electrospray thrusters traditionally offered an efficient electric propulsion option for small satellites by accelerating ionic liquid propellant through a voltage difference. This voltage difference formed a Taylor cone, from which ions and charged droplets ejected at high speed, generating thrust. Propellant feeding methods vary, with some using external wicking structures and others relying on internal capillary channels. Internal feeding, essential for scaling thrust with multiple parallel emitters, face a key challenge: distributing propellant evenly.
“A single emitter gives limited thrust. To reach practical levels, we needed multiple emitters functioning in parallel. But that only works if each one receives the same amount of propellant, which required precise manufacturing,” Kim explained.
Electrospray thrusters have worked best on missions that require fine control and sustained efficiency, such as deep-space exploration. Their continuous low thrust allowed spacecraft to maneuver gradually across vast distances, ideal for both transit and station-keeping. In low Earth orbit, they provide just enough push to counteract atmospheric drag. While chemical rockets deliver sharp, impulsive burns, electrospray engines achieve better fuel efficiency in long-duration tasks. Missions to Venus and beyond could benefit from an electrospray engine’s precise trajectory and high efficiency, enabling larger scientific payloads and longer mission lifespans.
Cleanrooms played a critical role in manufacturing these sensitive devices. Their tiny, precise components can’t tolerate dust or debris, which meant strict contamination control during assembly. However, advanced 3D printing methods are showing promise in reaching similar precision, potentially lowering costs and enabling future in-space production.
By combining in-space manufacturing with modular engine design, the team has created a more resilient, customizable, and cost-effective path for exploration. These advances could lead to a new era of spacecraft design, where repair, optimization, and evolution happens in orbit, enabling longer missions, smarter satellites, and deeper journeys into space.
Nicole Imeson is an engineer and writer in Calgary, Alberta.
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