A new concept for an astrobiology mission to Enceladus

This year’s Lunar Planetary Science Conference (2025 LPSC) saw some truly astounding presentations and proposals. These covered a wide range of science and exploration missions that address the priorities of NASA, other space agencies, and affiliated institutes. A major area of interest was future astrobiology missions that will search for evidence of biological processes (biosignatures) on extraterrestrial bodies. This included Mars, where most of our astrobiology efforts are focused, and locations in the outer solar system.

Consider Enceladus, Saturn’s icy moon known for the plume activity in its southern polar region. Based on planetary modeling, scientists theorize that these plumes are caused by tidal flexing in the moon’s interior. This causes Enceladus’ interior ocean to breach the surface (cryovolcanism) and hurl material into space. To confirm the presence of organics and (potentially) life, a team from NASA’s Jet Propulsion Laboratory (JPL) proposes an Enceladus Orbitlander to conduct in-situ measurements of Enceladus’ plumes.

The study was led by Alfred Nash, a JPL researcher, the winner of the JPL Principal Designation Award (2015) for Project Systems Engineering & Formulation, and the Lead Engineer of Team X, the JPL Advanced Design Team responsible for rapidly generating innovative space mission concepts. He was joined by his Team X JPL colleagues at the California Institute of Technology (Caltech).

According to their study, their mission proposal is consistent with the Planetary Science and Astrobiology Decadal Survey 2023–2032 (“Origins, Worlds, and Life”) released in 2022. In this survey, the National Academies of Sciences, Engineering, and Medicine (NASEM) committee established a Flagship mission to Enceladus (consisting of an orbiter and lander element) as the second-highest priority for missions developed before 2032:

“Study of plume material allows direct study of the ocean’s habitability, addressing a fundamental question: Is there life beyond Earth and if not, why not? Orbilander will analyze fresh plume material from orbit and during a 2-year landed mission. Its main science objectives are (1) to search for evidence of life; and (2) to obtain geochemical and geophysical context for life detection experiments.”

Ever since the Cassini-Huygens mission (2004–2017) studied Saturn and its largest moons, scientists have been eager to get a better look at Enceladus. Like Jupiter’s moon, Europa, and Saturn’s largest moon, Titan, Enceladus is considered one of the most promising places to look for extraterrestrial life in the solar system. Because of the distance between Earth and Saturn, mission concepts typically call for Radioisotope Thermoelectric Generators (RTGs) as a power source.

These nuclear batteries powered astrobiology missions like the Curiosity and Perseverance rovers and the Galileo and New Horizons spacecraft. At least three RTGs powered the Cassini orbiter, which was deemed necessary because solar panels are ineffective this far from the sun. However, as Nash and his team explain, NASA has indicated that the inventory of RTGs is limited due to their cost and complexity, particularly where their plutonium-238 fuel is concerned.

Mission architecture

The mission architecture that resulted consisted of a two-stage spacecraft comprised of a Lander and a Saturn Orbit Insertion (SOI) stage. This mission would launch in November 2038 using an expendable version of the Falcon Heavy rocket and a Star 48 solid rocket motor. This mission would spend the next 7.5 years traveling to Saturn, followed by a one-year Saturn approach and orbital transfer to Enceladus. This would be followed by half a year of fast flybys of Enceladus.

They estimate that the Orbitlander could sample plume material twelve times during this phase while flying 50 km (31 mi) from the surface at velocities of 5–9 km/s (3–5.5 mi/s). This would be followed by a 2.6-year Saturn Tour and Enceladus Orbit Insertion (EOI) phase, where the spacecraft would perform gravity assists to lower its altitude and speed to 30 km (18.5 mi) and 500–900 m/s (0.3–0.5 mi/s). The mission will spend another 3.5 months and sample plume material eight more times.

The mission will then drop its altitude to 50 km (31 mi) and spend a year scouting for a landing site. The DDL phase will take place, followed by two years of surface operations, during which the lander will collect and analyze samples from the moon’s icy crust, including water and plume material that has refrozen on the surface. The team also presents an alternative New Frontiers (NF) Program mission, which is also consistent with recommendations put forth in the 2023 Decadal Survey:

“Should budgetary constraints not permit initiation of Orbilander, the committee includes the Enceladus Multiple Flyby (EMF) mission theme in NF. EMF provides an alternative pathway for progress this decade on the crucial question of ocean world habitability, albeit with greatly reduced sample volume, higher velocity of sample acquisition and associated degradation, and a smaller instrument component to support life-detection.”

Design

The team recommends a lower size, weight, power, and cost (SWaP-C) concept for their proposed Enceladus Orbitlander. Team X relied on standard tools and validated Institutional Cost Models (ICM) to evaluate their mission concept and incorporated technologies that could be developed within the next five years. These technologies were evaluated for their ability to minimize the spacecraft’s dry mass and enable the mission to accomplish its science objectives using only one next-generation RTG power system.

They forgo reaction wheels for attitude control and opt for cold gas bipropellant thrusters instead. A High-Performance Space Computer (HPSC) would handle command and data systems. An Intelligent Landing System Lite was chosen for Deorbit, Descent, and Landing (DDL). The power subsystem comprises a Distributed Power Architecture (DPA) and a Peak Power Tracker (PPT), which reduce the overall cable mass and ensure the RTG consistently runs at 30 volts, increasing the power available from the RTG.

These elements were all selected because they reduce the spacecraft’s total mass and power needs by half compared to instruments used today. The propulsion system leverages improvements made in Low-Temperature Cold Gas Systems to reduce the heater power requirements, while a series of composite overwrap tanks were chosen for their reduced mass. The Orbitlander will rely on a 10° half-angle X-band Medium Gain Antenna (MGA) and a Patch Array High-Gain Antenna (HGA) for communications.

Advanced Variable Radioisotope Heater Units (RHUs) will handle the spacecraft’s thermal systems, reducing the number of RHUs needed to heat the spacecraft’s thrusters and instruments. As the team concludes, these design choices result in a system with a launch mass 846 kg (1865 lbs) lighter than the Technical Risk and Cost Evaluation (TRACE) estimate from the Decadal Survey, and $900 million cheaper.

Conclusions

Overall, the team’s “power reduction first” design offers a cost-effective, lower-mass, and simplified concept for an astrobiology mission to Enceladus in the coming decades. By incorporating advanced and evolving technologies, they claim that this could result in an architecture capable of delivering a greater payload to the surface, providing enhanced science opportunities:

“This approach not only reduces launch vehicle requirements and overall mission cost but also ensures technical feasibility within the timeline constraints of the decade. These results underscore the viability of a lower SWaP-C approach as a pathway for accelerated progress this decade on the crucial question of ocean world habitability, providing an important step forward in advancing the scientific priorities outlined in the Decadal Survey.”