NASA’s Jet Propulsion Laboratory Team X is proposing major changes to the planned Orbilander mission, which aims to investigate whether life exists on one of the solar system’s most promising candidates: Saturn’s ice-covered moon, Enceladus.
One of Enceladus’s most intriguing features is the plumes erupting from its southern polar region, which models suggest result from tidal flexing of the ocean beneath the moon’s icy surface. In a process called “cryovolcanism,” liquid from the subsurface ocean bursts through the outer ice and into space.
JPL scientists advise that observing and analyzing these plumes could be one of the most efficient and effective ways to determine if Enceladus’s ocean contains organic material.
Prioritizing Enceladus
The National Academies of Sciences, Engineering, and Medicine (NASEM) identified a lander and orbiter mission to study Enceladus’s plumes as the second-highest priority in the Planetary Science and Astrobiology Decadal Survey 2023–2032, their 2022 plan for the next decade of space exploration. Dubbed the “Orbilander,” the mission would feature a spacecraft equipped with both a lander and an orbiter. Beyond investigating whether life exists beyond Earth, the survey notes that studying Enceladus may also shed light on why life does not emerge in seemingly habitable environments.
Alfred Nash of JPL led Team X in a new study focused on refining the Orbilander design. The study proposes a November 2038 launch date for the revised spacecraft, which would be carried into space aboard a Falcon Heavy Expendable rocket with a Star 48 kick-stage. The journey to Saturn would take approximately 7.5 years, followed by a one-year approach phase to orbit the moon rapidly for six months.
NASA Proposal
During its flybys, the spacecraft would collect plume samples on a dozen occasions before entering a 2.6-year phase of gradually lowering its altitude and speed. It would then collect lower-altitude plume samples eight times over 3.5 months. Afterward, the Orbilander would descend to its lowest orbital altitude—31 miles above Enceladus’s surface—to begin a year-long scouting mission to identify a suitable landing site.
Finally, the lander would descend to the surface for a two-year sample collection and analysis mission, investigating the icy crust and refrozen plume material.
The team also proposed a more cost-conscious backup plan if funding falls short of the full mission vision. This “Plan B” would involve a flyby-only mission to collect additional information about the moon’s ocean habitability. However, this pared-down approach would involve fewer instruments, lower sample volumes, and higher collection velocities—potentially increasing the risk of degrading or missing biological evidence.
Creating a Workable Spacecraft
Because Enceladus is too distant from the Sun for effective solar power collection, the spacecraft would be powered by a nuclear energy source called a Radioisotope Thermoelectric Generator (RTG)—a proven technology used in missions such as Galileo to Jupiter and the Mars Curiosity rover. However, RTGs require plutonium-238, and NASA’s material supply remains limited.
The design team focused on maximizing efficiency, examining every opportunity to reduce the Orbilander’s size, power requirements, mass, and cost. Some proposed technologies are still under development but are expected to be ready within five years. Thanks to these design changes, the spacecraft’s mass was reduced enough to require only a single RTG, compared to the three needed for the Cassini mission.
Instead of traditional reaction wheels, cold gas bipropellant thrusters would control the spacecraft’s attitude. An Intelligent Landing System would manage all descent phases from orbit to surface landing. The design also incorporates a Distributed Power Architecture and a Peak Power Tracker to maintain a consistent 30-volt output while reducing cable mass. The revisions cut the spacecraft’s mass by 1,865 pounds and reduced projected costs by $900 million.
The paper “Novel Architectures and Technologies for a Lower Swap-c Enceladus Orbilander Flagship” was presented at the Lunar Planetary Science Conference, March 10-14, 2025, in The Woodland, Texas.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.