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.