  Lunar caves are promising features for long-term and permanent human presence
on the moon. However, given their inaccessibility to imaging from survey
satellites, the concrete environment within the underground cavities is not
well known. Thus, to further the efforts of human presence on the moon, these
caves are to be explored by robotic systems. However, a set of environmental
factors make this exploration particularly challenging. Among those are the
very fine lunar dust that damages exposed sensors and actuators and the unknown
composition of the surface and obstacles within the cavity. One robotic system
that is particularly fit to meet these challenges is that of a spherical robot,
as the exterior shell completely separates the sensors and actuators from the
hazardous environment. This work introduces the mathematical description in the
form of a dynamic model of a novel locomotion approach for this form factor
that adds additional functionality. A set of telescopic linearly extending rods
moves the robot using a combination of pushing away from the ground and
leveraging the gravitational torque. The approach allows the system to
locomote, overcome objects by hoisting its center of gravity on top, and
transform into a terrestrial laser scanner by using the rods as a tripod.
