Saturn’s largest moon, Titan, has captivated scientists since Pioneer 11’s flyby in 1979. Subsequent missions, including Voyager and cassini-Huygens, have only deepened the intrigue, revealing a celestial body unlike any other. Titan boasts a dense, nitrogen-rich atmosphere and a methanogenic cycle mirroring Earth’s water cycle.

Adding to its allure, Titan possesses a rich prebiotic surroundings and complex organic chemistry on its surface. These factors have fueled speculation about the possibility of life, perhaps in the form of simple organisms thriving in the vast methane lakes.

The Dragonfly Mission and Beyond

NASA is actively developing the Dragonfly mission,a nuclear-powered quadcopter slated to begin exploring Titan’s atmosphere and surface in 2034. But what about sending humans?

A recent study by Explore Titan suggests that spacecraft powered by nuclear fission could enable the first manned mission to the outer solar system. The research, conducted by William O’hara and Marcos Fernandez-Tous, was presented at the 56th Lunar Planetary Science Conference (LPSC 2025) in The Woodlands, Texas.

The Moon-Mars-Titan Trajectory

As the launch of NASA’s Constellation program in 2005, the long-term goal has been to extend human presence beyond Low Earth orbit (LEO). This strategy envisions a stepping-stone approach, building upon the Apollo-era lunar missions to establish infrastructure for eventual Mars expeditions.

Given that a Mars journey can take six to nine months, space agencies are exploring advanced propulsion methods to shorten travel times. Explore Titan, a non-profit institution, advocates for expanding this vision to include Titan. As their proposal states:

Of the possible candidates, Titan, the largest moon of Saturn, is the obvious candidate. Explore Titan suggests that the next Mantra after Moon-Mars becomes mars-Titan, where technology developed for human missions to mars can be expanded or evolved for use in Titan’s missions.

The Challenge of Distance and the Promise of Nuclear Power

The distance between Earth and Titan, approximately 8.5 astronomical units (AU), dwarfs the Earth-Mars distance of 0.5 AU. Reducing travel time is paramount to minimize crew exposure to microgravity and cosmic radiation.

Research into nuclear propulsion falls into two main categories: nuclear-thermal propulsion (NTP) and nuclear-electric propulsion (NEP). The Explore Titan team assessed the feasibility of both options for a manned mission to Titan with a one- to two-year transit time (one way). They evaluated the total mass of these systems (engines and propellant) and their impact on spacecraft design.

Their analysis began with NASA’s Design Reference Architecture 5.0 (DRA 5.0) NTP concept, which describes a 56.25-ton spacecraft suitable for crewed missions,utilizing a Uranium-235 reactor and hydrogen propellant for a roundtrip Mars mission.

Combined with 540 days of surface activities and an optimal launch window, this mission would last two and a half years. Such a duration poses important health risks to the crew, especially if extended for Titan missions.

The team also considered “Copernicus,” a larger NTP concept from a 2013 study led by NASA Glenn scientist Stanley K. Borowski. This vehicle, with a thrust capacity of 172 metric tons, could reduce one-way transit times to 150 to 220 days. However, the authors note that predictions have shown that even this duration of a mission in the deep space can exceed the permitted limits for exposure the crew to cosmic radiation.

While increasing Copernicus’s thrust could potentially reduce one-way transit times to 90 days, this would significantly increase the spacecraft’s mass and cost.

Alternative propulsion concepts, such as the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) presented by Ad Astra Rocket Company, were also examined. This concept uses a nuclear Magneto-hydrodynamic (MHD) reactor to power an electric propulsion system. A study by Franklin Diaz et al. suggested that this engine could reduce transit time to 149 days.

the team reviewed a 2020 study by Marco Gajeri et al., which demonstrated how a Direct Fusion Drive (DFD) could enable a robotic mission to Titan with a 2- to 2.6-year roundtrip. Optimized for a manned mission, these concepts could pave the way for human exploration of Titan.

The team concluded: From this study we conclude that nuclear space control systems can be the key for future missions to Titan. for manned missions, it could be the moast critical element for their success in view of the health risks of manned space flights at great depth.