For a while I’ve posited that the most cost-effective method of traveling on Mars, after you have some people there and some outposts going, is the “road train”, large motor vehicles hooked up in tandem, much like what we see in the Australian Outback, which, like Mars, is a remote desert bereft of much pre-existing infrastructure. More recently I’ve been thinking: why even have a fixed colony at all, when you could mount the whole colony on wheels and explore the whole planet instead of just one spot?
It’s really not that crazy. The most effective power source on Mars would be a nuclear reactor, and nuclear’s power density improves dramatically the bigger the reactor gets. Vehicles are also harder and harder to power with non-nuclear energy the larger they get. So if you want to make the most of your nuclear power technology you’ll want big vehicles, which is something you’ll probably want anyway on Mars. There’s a synergy there in my view that makes perfect sense: big nuclear road trains as your colonies.
Go Big or go Home
How big are we talking about? I’ve been envisioning something very roughly the same size as the Juggernaut from Star Wars for the locomotive and each “car” on the road train. My own back-of-the-envelope calculations I did years ago show that an off-the-shelf reactor will be much more efficient than any chemical fuel, and enable speeds at least as fast as a conventional vehicle, once you reach the size of the super-heavy Panzers the Germans were studying in World War II. That’s the size where nuclear really takes off as a power source and the vehicle achieves levels of utility familiar to Earthlings.
The Landkreuzer P. 1000 Ratte, for example, was to be 1000 tons in mass, 115 feet in length, 46 feet in width, and 36 feet in height, crewed by 20-40 people. My own research into nuclear trains online suggests also that nuclear starts to be competitive for trains once you reach Breitspurbahn gauge or so, roughly comparable in size to the super-heavy panzers with each car being 140 feet long, 20 feet wide, and 23 feet high. Both of these programs were Nazi projects; the greatest obstacle they faced, insufficient power density to drive the vehicles, would have been obviated by nuclear reactors, so maybe the Allies should count their lucky stars the Nazis didn’t have access to nuclear technology…
The Juggernaut from Star Wars
There’s more energy cost to transporting a whole colony around, but since any Mars colony sooner or later is going to be using a nuclear reactor anyway the marginal cost of just making the reactor a bit bigger is rather minimal.
The only real issue that I can think of, and that has been brought up when I first suggested it on the Fediverse, is ground pressure. A vehicle like this, especially a nuclear version, is going to be pretty heavy. Might it cause the ground to crack under it or shake too much for its own good? I honestly don’t think so.
Monster Vehicles: real-life Precedents
Consider that the heaviest self-propelled vehicle in the world today is the NASA crawler-transporter, massing 2700 tons and measuring 131 feet long and 114 feet wide. Ground pressure seems to be of no concern; only two tank-style treads per corner are needed. Originally designed to carry a Saturn V, which masses almost 3000 tons, the total mass it’s designed to transport is 5700 tons. It moves its payloads only very slowly, but it could easily be made to move much faster if it had an on-board nuclear reactor; in addition to not wanting it to move fast (wouldn’t want those big rockets to be shaken off their pedestals!), presumably political factors keep this from happening, much like how our largest cargo ships and cruise liners aren’t nuclearized yet despite having more than enough mass for it to be more economical than diesel.
The NASA crawler transporter. Looks suspiciously similar to the German plans for the Landkreuzer P. 1500 Monster self-propelled gun.
The very heaviest land vehicle, though, is not NASA’s crawler-transporter, but rather the Bagger 293, built by Krupp (of course it would be German…) in 1995 for TAKRAF to excavate their coal mines. This monstrosity masses 14,200 tons, almost three times as heavy as a fully-laden NASA crawler-transporter. It’s powered by an external electrical hookup, so doesn’t count as self-propelled, but as you can see in the picture below of its very similar sister vehicle, the Bagger 288, twelve tank-style treads distribute the weight onto the ground just fine.
Image © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)
So it seems like these monstrosities could move just fine through the trackless deserts of Mars, though very large wheels would be required. Yes, wheels; treads are in principle more mobile over obstacles and they do spread weight around better, but they’re much more mechanically complex and prone to breakdown, which is not something you want in a place like the Red Planet.
Monowheels for Mars?
So the future would seem to be one of these wheeled monstrosities a la the Star Wars Juggernaut traipsing around the rusty desert. Or is it? Even more recently I’ve thought of another alternative: the monowheel. This too is a type of vehicle that, like the Juggernaut, appeared in “Revenge of the Sith”; in Star Wars it’s best known as being General Grievous’s ride of choice.
The Tsmeu-6 personal wheel bike with its most famous driver.
Yes, it’s just one big wheel instead of twelve small wheels or whatever a conventional vehicle would use. Monowheels are almost exclusively found in single-passenger configurations such as this, but in principle I haven’t found anything that suggests it’s unviable for larger vehicles, potentially very large vehicles. Like the Martian monsters I’m talking about.
The monowheel’s advantage, aside from its mechanical simplicity, is low ground pressure; since the vehicle’s cabin sits inside the wheel, the wheel itself can be made arbitrarily large relative to the payload, ensuring large vehicles won’t create too heavy a footprint for the ground to handle. They also share treads’ ability to roll over obstacles with ease; the simple tumbleweed rather infamously rolls over anything and everything in its path, and it operates on the monowheel principle.
The monowheel’s disadvantages include not being able to see directly forward of you, as the wheel is in front of the cabin, though on a large vehicle there could be protruding retractable masts containing lookout cabins. Turning is relatively difficult, as the wheel is basically a giant gyroscope, but leaning the vehicle (ideally just the wheel, with the cabin maintaining the same orientation) toward one side or the other works well enough.
The biggest obstacle, however, is braking; brake too fast and you’ll do what’s called “gerbiling”, spinning the opposite direction to the wheel on the inside rather than coming to a stop. On the traffic-choked tree-ensconced streets of Earth that makes driving a monowheel a rather dangerous proposition, but in the desert of Mars, where you could easily be thousands of miles away from the nearest human being and in any case have horizon-to-horizon visibility, that doesn’t seem like much of a problem; why would you need to brake rapidly in such an environment?
So it’s possible that in the Martian future the monowheel’s time may come. That’s an interesting thought. The vehicles I’m thinking of would probably be 100 to 200 feet long, so to accommodate something like that in a monowheel the wheel will need to be several hundred feet high. Already we’re talking heights that are nearing proportions usually associated with skyscrapers! And we’re just getting started; even larger subsequent generations might sport wheel heights comparable to the Chrysler Building! Below is an artwork I’ve made depicting such a wheel, in this case all alone:
Gives the phrase “the Wheel of Power” a whole new meaning, doesn’t it? (Only Acceleracers fans will get this one…).
One might wonder how such vehicles could hook up to form a road train, but if you simply hook them up on the outside of the wheels and loop them back in once you get inside the length of the subsequent wheel it should work, though the radius of these joints will limit how much the wheel can turn, as it turns by leaning, unless they’re flexible and can stretch a great deal or (and this is the more likely solution) if the cabin simply leans along with the wheel. Presumably turns would be planned out to be gentle, giving a feeling similar to being on a ship at sea.
Monowheels have in many science-fiction works been presumed to be the future, from what I gather mostly because they look so cool, but I think there is a real case to be made for them. It’s possible, of course, that the monowheel’s advantages won’t prove insurmountable even on Mars and they might coexist with conventional vehicles.
In particular, if you want a colony where the cars can be flush with each other, much like in an articulated bus, you pretty much have to use a conventional wheels-at-the-bottom configuration, since the articulated joints would in a monowheel design conflict with where the wheel needs to go, leaving only relatively narrow corridors between the cars looping on the outside of the wheels. For something like an ore or cargo transporter, though, this would be of no concern.
A configuration that’s effectively two wheels, just side-by-side a la a Segway, is another possibility if a link through the inside is desired rather than the outside.
Quite interesting, these machines. Mars will likely have an extreme labor shortage for a very long time to come, so anything that can be automated will be automated, leading to the most sublime forms of high industrialism. Imagine deep pits being mined out by giant nuclear-powered machines of Godzilla-like proportions being tended to by just a couple of guys, their only visitors being even more massive nuclear-powered monowheel road trains appearing like ghosts out of a dust storm to be handed their load of cargo.
Applications for Worldbuilding
In my universe I just might go with that atmosphere, and monowheels being common, even if not ubiquitous, on the Red Planet, the typical colony being on wheels, with only mines and truly large habitats like domed-up craters being fixed-site. From what little I’ve been able to find Mars apparently has higher uranium and thorium content than Earth, and like Earth and unlike every other easily-accessible body in the solar system these metals have been concentrated into ore deposits. The real kicker is that Mars’s escape velocity is much less than the Earth, meaning not only are there higher concentrations of ore on Mars, not only is there more than enough for the few locals, but it’s also cheaper to export to other sites in space.
Just as carbon-dioxide-rich Venus in my space-opera setting basically owns the carbon industry by the end of the 21st century, so uranium-and-thorium-rich Mars basically owns the nuclear fission industry. Population will go where it wills, but they’ll want their natural resources as cheap as possible, and if Mars is the cheapest place to get them that’s where they’ll be mined. Lighter and more common materials will mostly be sourced from asteroids, helium-3 and the like (fusion fuels) from the gas giants, but both of the big inner planets besides Earth will have an economic niche aside from being favored haunts of tourists, retirees, and scientists. Isn’t that cool? Amazing what you can think of if you look at the hard-science facts and use your imagination a bit.
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