Let’s say that you’ve just booked a ticket for a two-week holiday on the Moon, say, or on Mars, and you really want to spend some of your free time – when you’re not eating, reading or swimming in the Sea of Tranquility – on a bike because you love cycling. But you’re not sure there’ll be available bike-sharing – or, in fact, any bikes at all. Because the bicycle, as all means of transportation on Earth, depends on gravity to function, to provide traction for the wheels and to steer.
According to Professor Andy Ruina: “The controllability of a bicycle depends on gravity. Without gravity, lean and direction cannot be controlled independently.”
Dr Ruina and his team of researchers built a spring-loaded training-wheel bicycle that allowed riders to lean without toppling, simulating a zero-gravity environment where the bike’s wheels were magnetically attracted to the surface so the rider wouldn’t just go flying off into space. As illustrated in the video below, the rider was able to lean into a curve but unable to steer.
The problem for astronauts (or tourists) is that the force of gravity on Mars is only 38 per cent of that on Earth and on the Moon, it is only 16.7 per cent or 1/6 of our planet’s. While the problems would not be as severe as in a no-gravity environment, it’s apparent that a standard “earth bike” would not work in such low-gravity environments without significant changes.
From a practical perspective, a functional “moon bike” could be a sensible means of transportation for astronauts exploring other planets, since it would save fuel and provide exercise. And, as the great science-fiction writer Robert A. Heinlein has written, it could also be used to transport freight, such as ore.
“The solitary prospector, deprived of his traditional burro, found the bicycle an acceptable and reliable, if somewhat less congenial, substitute,” Heinlein wrote in his novel The Rolling Stones. “A miner’s bike would have looked odd in the streets of Stockholm; over-sized wheels, doughnut sand tires, towing yoke and trailer, battery trickle charger, two-way radio, saddle bags and Geiger-counter mount made it not the vehicle for a spin in the park — but on Mars or on the Moon it fitted its purpose the way a canoe fits a Canadian stream. ”
So it’s not surprising that the National Aeronautics and Space Administration (NASA) would be interested in solving the problem of using a bike in low-gravity conditions. One solution NASA has looked at is the HyperBike. Invented by Curtis DeForest as a new fitness toy for the Generation X crowd, the HyperBike – like racing wheelchairs – has heavily cambered wheels that are 64 inches (162.5 cm) apart at the road level and only 26 inches apart at the top of their 8-foot (2.43 m) diameter. It also positions its rider so that the bike’s centre of gravity is below the wheel axis, giving it greater stability.
It is that stability and the balance of weight relative to the spinning forces – which means your balance is no longer hanging precariously over the wheels – that interested NASA because these aspects would make the HyperBike a good option for low-gravity environments. The NASA-funded Space Alliance Technology Outreach Program even invested in the development of the next prototype. One can only hope that it will be a little more attractive. Otherwise, I’m not riding it.