Lunar Cave Explorer (spherical)
The Daedalus mission, funded by the European Space Agency, aims at the exploration and characterisation of lunar cave structures with a tightly integrated spherical robot. A sphere is ideally suited to protect sensors and scientific equipment in rough, uneven environments. In this study, a prototype of the spherical robot was developed and built to demonstrate and examine the movement capabilities of spherical systems through a double pendulum locomotion system.
Mission
Lunar orbiters have mapped multiple deep pits on the surface of the Moon, believed to be ‘skylights’ into lava caves. These are of high scientific interest, offering access to pristine lunar material – perhaps even water ice deposits. Such caves might also become habitats for lunar settlers, offering natural shielding against radiation, micrometeorites and surface temperature extremes.
The 46-cm diameter DAEDALUS sphere would carry an immersive stereoscopic camera, a LiDAR for 3D mapping of cave interiors, temperature sensors and a radiation dosimeter, as well as extendible arms to help clear obstacles and test rock properties.
The tether for lowering the sphere will be used for data communication and powering the equipment during the descending phase. During the exploration phase, the robot will be disconnected from the cable, and will use wireless communication.
Design objectives
In space, where human limitations are most palpable, the robot needs to be able to carry out the mission reliably and autonomously. Therefore, the design needs to adhere to the following objectives:
• high degree of mobility (e.g. precision, zero or small turn radius, suitable for lunar environ- ment)
• efficient and economic space management (e.g. reducing the needed space of the locomotion to a minimum)
• continuous reliability and functionality (e.g. vibration of launch, long-term operations)
Moreover, the spherical design, with no openings, is well suited to protect sensory equipment from lunar regolith.
Locomotion
Unlike most pendulum-driven robots that can only steer while in motion, this robot requires the ability to turn on the spot for maximum mobility. To achieve omnidirectional motion, we implemented a double pendulum system.
This method revolves around manipulating the sphere's center of mass to induce rotation. When a sphere's center of mass isn't directly over its ground contact point, it rolls until both align. The sphere's center of mass is adjusted using two motors connecting the outer shell to its inner framework. As these motors turn, they pivot the internal structure, shifting the center of mass and achieving motion.
To steer, two motors inside the sphere control two separate weights, shifting the center of mass perpendicular to the direction of motion, which guides the sphere to the left or right. Deflecting both weights in the opposite direction and spontaneously releasing them to fall back into their initial position allows the robot to turn on the spot.
Body structure
Though the robot will have LiDARs, cameras and ancillary payloads during the mission, this prototype’s objective is to demonstrate and examine the movement capabilities of spherical systems.
The robot employs the above locomotion system, using its battery packs, instead of additional weights, to shift the center of mass for steering purposes. Motion is achieved by two motors located on either side, tilting the entire platform either forward or backward. All electronic components and control units are mounted on this dual platform
Results
The videos show the first mobility tests.
Gallery
