Event Location: NSH 1507

Abstract: Excavating regolith, or loose soil, on the Moon and Mars enables outposts, fuel depots, and sustained space exploration. In space missions mass is always at a premium because it is the main driver behind launch costs. Low mass, especially when combined with reduced gravity, results in machines with limited weight available to produce traction or plunge tools into soil. Missions will start small and scale up, so robotic excavators that are productive across a range of light weights are essential.

This research proposes to identify a “lightweight threshold” that distinguishes regimes where continuous excavators exhibit higher productivity than discrete excavators and vice versa. Continuous excavators, which include bucket-wheels and trenchers, dig by taking cuts of soil with multiple small buckets in quick succession, while discrete excavators, such as loaders or scrapers, fill one larger bucket with a single cut. Continuous excavators are expected to maintain high productivity even below a lightweight threshold, where productivity drops off for discrete excavators. High payload ratio and driving speed also govern productivity of lightweight excavators.

A methodology is proposed for investigating lightweight excavation through analysis (including non-dimensional and sensitivity analyses), benchtop experimentation (digging with bucket-wheels as well as discrete buckets in controlled laboratory conditions), and field testing a robotic prototype (incorporating a novel continuous excavator configuration).

Past lightweight excavator prototypes were too slow or carried too little regolith payload. Some used bucket-wheels or bucket-ladders to dig continuously, but transported regolith using exposed chains or conveyors that would not withstand abrasive Lunar regolith.

Field tests with a novel robotic excavator will demonstrate how digging with bucket-wheels, hauling in high payload ratio dump beds, and driving at high speed make lightweight excavators productive for a range of relevant space mission scenarios.

Productivity and energy-efficiency tradeoffs between continuous and discrete excavators identified in this work will be generalized for applicability to terrestrial mining and construction.

Committee:David Wettergreen, Co-chair

Red Whittaker, Co-chair

Dimi Apostolopoulos

Karl Iagnemma, MIT