  An emerging paradigm is being embraced in the conceptualization of future
planetary exploration missions. Ambitious objectives and increasingly demanding
mission constraints stress the importance associated with faster surface
mobility. Driving speeds approaching or surpassing 1 m/s have been rarely used
and their effect on performance is today unclear. This study presents
experimental evidence and preliminary observations on the impact that
increasing velocity has on the tractive performance of planetary rovers.
Single-wheel driving tests were conducted using two different metallic,
grousered wheels-one rigid and one flexible-over two different soils, olivine
sand and CaCO3-based silty soil. Experiments were conducted at speeds between
0.01-1 m/s throughout an ample range of slip ratios (5-90%). Three performance
metrics were evaluated: drawbar pull coefficient, wheel sinkage, and tractive
efficiency. Results showed similar data trends among all the cases
investigated. Drawbar pull and tractive efficiency considerably decreased for
speeds beyond 0.2 m/s. Wheel sinkage, unlike what published evidence suggested,
increased with increasing velocities. The flexible wheel performed the best at
1m/s, exhibiting 2 times higher drawbar pull and efficiency with 18% lower
sinkage under low slip conditions. Although similar data trends were obtained,
a different wheel-soil interactive behavior was observed when driving over the
different soils. Overall, despite the performance reduction experienced at
higher velocities, a speed in the range of 0.2-0.3 m/s would enable 5-10 times
faster traverses, compared to current rovers driving capability, while only
diminishing drawbar pull and efficiency by 7%. The measurements collected and
the analysis presented here lay the groundwork for initial stages in the
development of new locomotion subsystems for planetary surface exploration. At
the same time...
