NASA has funded an early-stage concept through its NASA Innovative Advanced Concepts (NIAC) program to develop spherical “aerobots” named SPARK, short for Solid-state Propulsion for Autonomous Reconnaissance of Karst. Led by Daniel Drew, an assistant professor at the University of Hawaii at Mānoa, the project aims to design flying vehicles capable of navigating the extreme near-cryogenic conditions and subterranean caves of Saturn’s moon, Titan.
Titan stands out as one of the most Earthlike bodies in our solar system, featuring surface rivers, lakes, and seas composed of liquid hydrocarbons like methane and ethane. The moon also hosts a complex karst terrain defined by underground sinkholes and caves. Standard rovers would struggle to traverse this landscape. Flying vehicles, however, may have more success.
The Engineering Challenge of Electrohydrodynamic Propulsion
To operate in Titan’s dense atmosphere, the SPARK concept relies on electrohydrodynamic (EHD) propulsion. Also known as ion or electric thrusters, these systems utilize high voltages to accelerate ions, creating thrust. Daniel Drew has researched this technology since his graduate studies at the University of California, Berkeley, supported by a National Science Foundation fellowship.
EHD propulsion draws inspiration from the hobbyist “lifter” community. Builders traditionally construct these triangular prototypes using balsa wood, magnet wire, and aluminum foil, driving them with up to 40,000 volts drawn from flyback transformers scavenged from microwave ovens or CRT monitors. While hobbyist setups are crude, early studies by NASA and the Air Force, alongside parallel research groups like an MIT-led team examining Earthborne aircraft, have validated the underlying physics.
Drew’s previous work includes microfabricated centimeter-scale flying robots propelled by atmospheric ion thrusters. According to Space.com, his accomplishments include the first demonstration of microfabricated EHD actuators and the takeoff of a centimeter-scale “ionocraft” carrying a payload. Most recently, the team published the design and takeoff of the first ion-propelled micro-hovercraft in a preprint server arXiv paper.
Mission Timelines and the Shadow of Dragonfly
The SPARK project is currently backed by a nine-month Phase 1 NIAC grant. According to project lead Daniel Drew speaking to Space.com, the initiative must subsequently clear an up-to-two-year Phase 2 development cycle before things look “more realistic” for a liftoff.
NASA’s Dragonfly mission to Titan is currently targeted for a 2028 launch. It remains unclear whether SPARK will mature quickly enough to integrate into the primary Dragonfly mission timeline. However, any potential delays to Dragonfly could open possibilities for late-mission additions.
“Where does that line up with the current Titan mission timeline, assuming we’ve missed the window for Dragonfly? I don’t know,” Drew noted to Space.com regarding the development schedule.
Despite scheduling uncertainties, developers project that ion thrusters will provide vital operational persistence, maneuverability, and robustness to the near-cryogenic conditions. Furthermore, EHD propulsion minimizes downwash disturbances of scientifically-important hydrocarbon layering.
Targeting a Legacy Similar to Mars Ingenuity
The ultimate ambition for the SPARK aerobots is to function as a cave-exploration forerunner on Titan, drawing a parallel to the Ingenuity helicopter on Mars that made 72 flights. While Ingenuity was originally designed for a demonstration mission, it ultimately completed more than tenfold what it was supposed to do.
Developing SPARK requires navigating a very small field of specialized researchers. As Daniel Drew stated to Space.com, “These [prototypes] are triangular balsa wood, magnet wire, and aluminum foil prototypes.” He added regarding the broader academic landscape, “That may seem like a pretty decent list of significant milestones, but it’s really not a crowded space of people working on this topic. I’m mostly racing against myself here.”
As Phase 1 progresses, the engineering focus shifts toward evaluating the benefits of EHD propulsion, such as its scalability.
