Possibly thousands, with the propensity of wheels for exploding. In a more serious note that's the benefit of living in our civilisation, we can experiment and

Possibly thousands, with the propensity of wheels for exploding. In a more serious note that's the benefit of living in our civilisation, we can experiment and do what we want to even if it has no measurable long term or commercial benefit. Or if someone got there first, why not have a go, could pay off (for example, SpaceX had a go)