Rules of thumb and heavy dependence on experience seem to work quite well. However, when one tries to predict how things will react in another environment, one usually relies on well-understood theoretical relationships developed in the existing environment. One particular area of interest is excavating activities. The large mass of this equipment is useful since it allows the machine to exert more force during the excavating operation and thereby extract a larger portion of soil in the excavating bucket or other implement. The high excavating force available is a function of the mass of the machine and gravity which work together to keep the machine in contact with the ground.
More mass is better and more gravity is better.
This complicates matters when considering excavating operations on Mars or the Moon. This translates into less force available for excavating. Additionally, sending mass to the Moon or Mars is very expensive, so we will wish to send as little as possible. Both of these conditions plus the lack of rigorous theoretical models imply that our ability to predict the performance of excavating machines sent to Mars or the Moon is very limited. A better understanding of the effects of gravity on digging forces is needed.