As a first approximation, we can assume traction capability is roughly proportional to flat-surface friction. For non-slipping wheels,
- Max Friction Force = Normal Force * Coefficient of Static Friction.
On the moon, surface gravity is 16.5% of Earth surface gravity. So, normal force would be 16.5% of an equivalent Earth value.
In a maximum performance turn of a wheeled vehicle, the maximum friction force of the wheel is used to accelerate the vehicle in circular motion.
- Centripetal acceleration = velocity^2 / turn radius.
Let's use maximum performance turn radius as a gravity-independent metric for the "safety" of a speed. For a certain rover of known mass and wheel/surface coefficient of friction, we can calculate the maximum speed for a target turn radius by (1) finding maximum acceleration due to friction and (2) solving for velocity.
A dune buggy on Earth can be driven safely over rocky sand at 30 mph (guess).
On the Moon, there is only 16.5% of the available acceleration due to wheel friction because there is 16.5% of the gravity causing normal force.
So, for the same turning radius,
- velocity = sqrt(centripetal acceleration * turn radius)
A 0.165x multiplier on acceleration corresponds to a 0.406x multiplier on velocity.
The maximum safe speed of that dune buggy on similar surface on the moon is 12.2 mph.
Effects not modeled
- Non-flat terrain
- Lunar surface regolith having different properties than Earth regolith
- Increased rollover risk due to lower gravity
- Extreme consequences from collisions