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Human-Powered Rover Conceptual Notes

At the lunar outpost, there will be a need for different sorts of vehicles, and undoubtedly large hauling vehicles, whenever they are required, will need a good power source. They will likely be some high-output fuel cells, solar arrays or some similar technology.

But the type of vehicle needed for a small relatively self sufficient group should have a number of characteristics that few of the designs in the literature ever consider.

If you look at this problem with the eyes of an engineer you immediately come to the conclusion that a human powered vehicle is just the ticket.

Research backs this up. In a Scientific American issue on Human Powered Vehicles a number of years ago, an article on bicycles had an extra data point for the performance of a vehicle on the moon. A racing biker, with no air resistance and 1/6 g could break 1000km/h in sprints. A normal, healthy person could cruise at over 100km/h all day, and could easily pull a trailer load at the equivalent of typical earth bound auto driving speeds.

The form of the vehicle is the recumbent bicycle like that used by Stephen K. Roberts (Computing Across America). And in fact, he would probably be the best person to speak to on the design of a lunar rover. He crossed the USA from end to end several times on his recumbent, traveling up and down through the Rockies, keeping up reasonable highway speeds, and all the while pulling a trailer that included solar power gathering and a satellite uplink so he could type on the keyboard in front of him (while peddling) and submit articles to magazines that funded his journeys. He also had navigation and maps built into his console processor. There is little that a lunar rover built for days of unsupported prospecting would need that he didn't do 5-6 years ago.

Now that is not to say there aren't issues unique to the moon. There is the issue of traction and off road travel which will drive the gearing ratios, axle loading, weight and balance, and wheel design. Braking will have to be dynamic, feeding the energy back into a dynamo. Normal friction brakes are a bad idea for two reasons, (1) the abrasiveness of the regolith; and (2) brake cooling is purely by radiation to the background and conduction through the frame. Radiators are a problem as has been suggested before; and since I expect the frame to be composites, conduction is not very good either.

Gears and chains and deraileurs will have to be very robust and spares will be required. A design that can be field-welded would be a good idea. Better to trade off a bit of elegance and performance for field maintainability. These parts can be built very ruggedly (we're not talking about racing bikes here) and would need to be able to withstand the rigors of large temperature swings and abrasive particles. One could seal them, but then it is more difficult to field-strip. And not to mention which, without herculean efforts the lunar grit will get in anyway. Desert Storm is a case in point.

Another area of concern is space suit cooling. The loads will not be excessive under normal cruising since the peddling is only enough to replace frictional losses.

Use of a small motor like that in a minibike could solve a number of problems (if they don't add too much complexity on their own). The motor could be the means by which braking returns energy to storage. Energy can be recovered on downhill stretches and used to ease uphill travel. It also can reduce the heat-loading on the space suit during acceleration from a standing start, or indeed any acceleration under load.

The motor would of course need to be built such that it can be disconnected from the system entirely if it fails. The overall system would have to be able to get the lunatic back home reqardless. So think of it only as a luxury item on the bike.

The suit would be a live-in suit, so that puts some extra design load on it. You might have to do better than a diaper if you're going to be out for a week, but this is a problem that needs to be solved anyway. The Star Wars rovers that some NASA scenarios show us are not going to be feasible on any realistic budget, and in any case you'd only be able to afford one of them for the cost of giving every lunatic their own personal lunabike.

Regolith Handlers

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