Abstract DGP2026-113

Future exploration of small bodies and low gravity moons increasingly relies on spacecraft that must operate in close proximity to poorly characterized surfaces and subsurfaces. Missions targeting asteroids or (icy) moons such as Enceladus face combined challenges of safe landing or hopping operations, limited a priori knowledge of surface properties and the scientific need to probe subsurface structures and stratigraphy. Radar instruments are uniquely suited to address these challenges, as they provide direct, physics-based measurements that are largely independent of illumination conditions and surface contrast.

This contribution presents a compact, coherent dual-channel frequency modulated continous wave (FMCW) radar, designed as a hybrid instrument combining radar altimetry for landing and proximity operations with ground-penetrating radar (GPR) capabilities for subsurface investigations after surface contact. The instrument is implemented in a form factor of less than half a CubeSat unit and is optimized for low power consumption of less than 2W and high configurability, enabling its use on small landers, hopping platforms, drones or sample-return probes. The radar architecture supports operation over a wide frequency range from 10 MHz to 6 GHz , with the mission-specific operating frequency selected according to scientific objectives, antenna implementation, and interference constraints.

During descent and surface approach, the radar operates as a terrain-relative altimeter, providing continuous measurements of ground clearance, relative angle and closing velocity from distances up to 10km. These observables are particularly relevant for missions to low-gravity bodies, where conventional navigation sensors may be challenged by irregular shapes, low surface contrast, dust or dynamic illumination conditions. In this context, the radar altimeter mode serves as a safety-critical subsystem augmenting LIDAR sensors and supporting landing or hopping maneuvers. Additionally it aids touchdown detection, post-landing state estimation and estimation of local dielectric properties.

Following landing or surface contact, the same hardware can be reconfigured to operate as a GPR. In this mode, the instrument is sensitive to subsurface dielectric contrasts and is designed to probe depths ranging from tens to approximately one hundred meters in regolith up to the kilometer scale in low-loss ice, depending on material properties and operating frequency. For icy moons such as Enceladus, this capability is relevant to studies of regolith thickness and structure, ice layering, and the near-surface expression of geological or cryovolcanic processes. On asteroids, GPR measurements can provide constraints on internal structure, porosity, and block size distribution, which are critical parameters for understanding formation processes and for the interpretation of returned samples.

The coherent radar architecture further enables advanced processing techniques, including the potential for interferometric or synthetic-aperture methods during surface hopping or controlled motion phases.

By integrating landing support and subsurface sounding into one reconfigurable radar instrument, this approach offers a pathway toward increased scientific return and mission robustness for future exploration of small bodies and moons, particularly in the context of resource-constrained missions and sample-return architectures.