Advantageous bucket-wheel configuration for lightweight planetary excavators

Abstract

Robotic regolith excavation on the Moon and Mars enables outposts, fuel depots, and sustained space exploration. In any space mission, mass is always at a premium because it is the main driver behind launch costs. Low mass and reduced gravity (1/6 of Earth gravity on the Moon, 1/3 on Mars) results in machines with limited weight available to produce traction or plunge tools into regolith. Bucket-wheel excavators have been shown to produce low resistance forces that enable lightweight operation, but in the past have had difficulty transferring regolith from bucket-wheel to collection bin. Exposed conveyors and chains fare poorly in harsh lunar regolith and vacuum. A novel excavator configuration, with bucket-wheel mounted centrally and transverse to driving direction, achieves direct transfer into a collection bin. Experiments with a bucket-wheel digging in lunar simulant show that transverse bucket-wheel orientation does not increase resistance significantly. Excavation resistance is shown to depend mostly on the ratio of bucket-wheel rotation rate to forward advance rate.