Dragonfly, a Pu-fueled drone heading to Titan, gets key NASA approval
Curiosity landed on Mars sporting a radioisotope thermoelectric generator (RTG) in 2012, and a second NASA rover, Perseverance, landed in 2021. Both are still rolling across the red planet in the name of science. Another exploratory craft with a similar plutonium-238–fueled RTG but a very different mission—to fly between multiple test sites on Titan, Saturn’s largest moon—recently got one step closer to deployment.
On April 25, NASA and the Johns Hopkins University Applied Physics Laboratory (APL) announced that the Dragonfly mission to Saturn’s icy moon passed its critical design review. “Passing this mission milestone means that Dragonfly’s mission design, fabrication, integration, and test plans are all approved, and the mission can now turn its attention to the construction of the spacecraft itself,” according to NASA.
If all goes as planned, Dragonfly could be launched onboard a SpaceX Falcon Heavy rocket at NASA’s Kennedy Space Center in Florida in 2028. Almost seven years after launch, it would land on Titan.
Mission to Titan: According to the APL, which is managing the mission for NASA, the flying machine—technically a rotorcraft or quadcopter drone—will go airborne to move from one area of interest to the next on Titan and cover more ground as a result.
Dragonfly is to sample materials and analyze the moon’s surface composition in different areas to characterize the habitability of Titan's environment, study prebiotic chemical processes, and search for chemical signatures that could indicate water- and/or hydrocarbon-based life.
“I’m so proud of what this team has accomplished in bringing this audacious mission to reality,” said Dragonfly principal investigator Elizabeth “Zibi” Turtle, of APL. “After years of design and testing, we are excited to start building Dragonfly itself and prepare for its game-changing voyage of exploration across an intriguing, mysterious ocean world.”
Titan is rich in organic molecules, and according to APL it is the only moon in the solar system with a dense atmosphere and an earthlike hydrological cycle of clouds, rain, and liquid flowing across the surface to fill lakes and seas—but in Titan’s case, the liquid is methane (CH4). Titan's atmosphere of 95 percent nitrogen is four times denser than Earth's, and its gravity is about one-seventh of Earth's. Both characteristics boost the feasibility of flying what APL calls a “car-sized drone.”
Titan’s atmosphere makes it difficult to get clear images of the moon. NASA’s Cassini spacecraft (also powered by an RTG) arrived in July 2004 and used radar and imaging at near-infrared wavelengths to map Titan's surface and study its atmosphere, while its Huygens probe parachuted to the surface to collect more data. The studies confirmed that Titan’s surface features vast sand dunes as well as hydrocarbon rivers, lakes, and seas.
Dragonfly specs: Dragonfly will have a mass of about 875 kilograms and be 3.85 meters (about 12.5 feet) wide and long and 1.75 meters (about 5.5 feet) tall, according to APL. It will be powered by a 134-ampere-hour battery, which will charge during Titan’s night (eight Earth days) by an onboard RTG. Heat from the RTG will also provide conductive thermal control during the journey to Titan, and convective thermal control while Dragonfly operates on Titan.
Flight, data transmission, and most science operations will occur during Titan's daytime hours (eight Earth days). APL anticipates that Dragonfly will make one “hop” per full Titan day (16 Earth days), and the craft could travel from its initial landing site to areas several hundred kilometers away during its planned 3.3-year mission.
This image is displayed in NASA’s “MMRTG Pull-apart Animation” video. (Image: NASA)
Power provisions: The RTG model that Dragonfly will carry is known as a multi-mission radioisotope thermoelectric generator (MMRTG), which is designed to be used either in space or within the atmosphere of a planet (or in Titan’s case, a moon). It’s the same RTG model that Curiosity and Perseverance carried to Mars.
To power its exploratory craft, NASA is sourcing Pu-238 from the Department of Energy, which relies on the expertise and capabilities of the Idaho, Los Alamos, and Oak Ridge National Laboratories to assemble an MMRTG.
Inside the MMRTG is a stack of eight modules, each containing cylindrical Pu-238 dioxide fuel pellets clad in iridium. The cladded pellets sit inside a graphite impact shell, which is inside a carbon fiber sleeve that gets inserted into the cuboid aeroshell, or module. The heat from the eight fueled modules is converted into electricity by thermocouples. Check out NASA’s MMRTG animation to see the device from the inside out.
