Encealdus Orbilander: A Flagship Mission Concept for Astrobiology

"Whether life exists beyond Earth remains a fundamental question driving our exploration of the Solar
System. At Saturn’s moon Enceladus, plumes of oceanic material vented into space allow the investigation of the astrobiological potential of an ocean world, hinted at by Cassini, without the necessity of
drilling through kilometers of ice crust.
The Enceladus Orbilander is a flagship ($2.56B in fiscal year 2025 dollars) mission concept created for
the 2023–2033 Planetary Science Decadal Survey. Orbilander takes full advantage of the opportunity provided by Enceladus’ plumes to search for signs of life. A single spacecraft both orbits and lands,
capturing samples from four distinct reservoirs offered by the plumes. These samples, both particulate
and vapor, are then analyzed by the Life Detection Suite (LDS), a set of five instruments conducting
complementary and orthogonal biosignature-seeking measurements. To provide the context that specifically enhances interpretation of LDS measurements, geochemical and geophysical investigations are
conducted both in orbit and on the surface. These reveal the physio-chemical state of the ocean and core
as well as the processes involved in ejection of plume material and how these affect the ocean material
analyzed by the LDS.
The Orbilander can be delivered to the Saturn system via several launch vehicle and trajectory options,
including a direct trajectory (7-year cruise), a ∆V-EGA trajectory (9-year cruise) and several options using an inner cruise with Venus and Earth flybys (10-year cruise). Upon Saturn Orbit Insertion, a 4-year
moon tour pumps down the Orbilander’s orbit to intercept Enceladus. The most optimal arrival times balance the Jupiter flyby opportunities of the late 2030s and solar illumination at the Enceladus high
southern latitudes where plume material is most abundant. This mission concept therefore targets project
start in 2030.
Upon Enceladus Orbit Insertion, the Orbilander begins a 1.5-year-long campaign of landing site reconnaissance, remote sensing science, and collecting sufficient plume sample to run all but one of the LDS
measurements. After successful landing, the Orbilander spends 2 years on the surface conducting multiple
LDS measurements with all five instruments on actively and passively collected plume material, as well
as seismic investigations. The schedule laid out here is well-defined, but the mission also has operational
and resource flexibility should additional reconnaissance be needed.
As part of the design study, mission and development risks were identified and mitigation strategies proposed. Technologies key to achieving the life detection science objectives include instrumentation
matured under programs like COLDTech and ICEE-2, such as aspects of the sampling system and microfluidic devices, as well as well-known techniques like high-resolution and separation-capable mass
spectrometers. Autonomous onboard navigation is planned to maintain a halo orbit around Enceladus to
enable passive sampling from orbit as well as reconnaissance measurements for use in site selection and
landing. Terrain relative navigation is included to ensure safe landing, given that targeted areas may contain landing hazards. Continued development of radioisotope thermoelectric generator (RTG) technology
and long-life batteries is essential for this long duration mission.
The Enceladus Orbilander represents an optimal point in the trade space of science value versus cost, taking advantage of the extensive knowledge of Enceladus provided by Cassini, how well Enceladus lends
itself to a search for life in material from its ocean, and the flexibility afforded by the innovative design
developed by the APL team. By taking full advantage of Enceladus’ plumes both in orbit and on the surface, Orbilander represents a robust search for life with complementary and orthogonal biosignatures as
well as contextual geophysical and geochemical measurements, determining not only whether Enceladus
is inhabited (at levels up to 500,000× scarcer than in Earth’s oceans) but also why. "