In watching the most recent episode of Top Gear, I was reminded of an interesting tidbit by James May’s segment on the Lunar Roving Vehicle, or “moon buggy”. In reviewing the Mark II LRV, he commented that the tires for it were borrowed from a piece of farm equipment. Interestingly, he never touched on the fact that those tires would only be there as mock-ups for the actual tires.
A piece of trivia that so many people tend to overlook is the fact that conventional tires simply would not work on the moon. This is true for several reasons. Firstly, the temperature variances are enormous. During “night” on the moon, it gets colder than -150°C. During “day” on the moon, it exceeds 100°C. Anyone who has tried to use all-season tires in the temperature extremes in Alberta, where it can approach 40°C in the summer, and -40°C in the winter, will know that there are very few rubber compounds that can handle that variance.
In addition, the surface of the moon is exposed to the vacuum of space. As such, attempting to inflate a tire would be difficult, and likely dangerous. Any pressure inside the tire would be counteracting the massive absence of pressure outside the tire, and the risk of a blowout would be enormous.
As such, the tires on the LRV are actually more analogous to tire-shaped springs. They are made entirely of zinc-coated steel, and provide cushioning through the tensile strength of the metal, in the same way as the springs in your car’s suspension cushion your ride. On the exterior of the tire, metal chevrons provide grip, in much the same fashion as the rubber blocks on a street tire.
It’s small details like this that start to reveal the enormous challenges of equipping a mission to the moon. Every little thing becomes an obstacle. Quite literally, these engineers had to reinvent the wheel.
Nevertheless, I still expect the next LRV to have spinners.