# What is the most effective way to build road on Mars and Moon?

It is simply a matter of time before human colonized our natural satellite and the red planet, so how to lay roads that is similar to ours on lunar and Martian soil? (For now suppose we are planning to build mega cities.)

• Constraints like Gravity, Friction etc. won't be the same. Would we need materials as resistant as what we have on Earth ? – Kii Oct 2 '15 at 11:35
• @Kil, no, we wouldn't need the same materials. – Green Oct 2 '15 at 12:50
• Are these road exposed to the atmosphere or in some form of protected environment? – Joe Bloggs Oct 2 '15 at 13:42
• If they are exposed to the atmosphere, a dust storm would probably bury them within a year. – JDSweetBeat Oct 2 '15 at 13:47
• Good answer touch on where to get resources for the road and outstanding answer will construct road suitable for all weather. Winning entry would use only locally available materials for the roads and that road is as good or even better quality than those seen on Earth. – user6760 Oct 2 '15 at 14:00

Roads on Mars and the Moon won't need to be built the same way that they are on Earth because gravity on those bodies is so much less.

Intuitively, the shear load when braking on a road is much smaller for a Mini Cooper compared to a fully loaded 18 wheel truck. The larger truck is pressing down on the road much harder than the small car, so the shear loads it exerts on the concrete or asphalt are much higher. So if we take the same two vehicles and put them on the moon, automatically, they will press down on the road much less. Lunar gravity is 1.622 $\text{m/s}^2$ and Mars 3.711 $\text{m/s}^2$.

Dirt roads may suffice for low traffic roads or for low weight vehicles. Thin concrete roads may be needed for high load or high traffic roads. Dust control may not be the prime issue for making roads but though roads would be a good approach for maintaining a pristine landscape. If the regolith particulate size is small enough then a heavily loaded truck may get stuck. A road will prevent that kind of sticking-in.

Regolith dust must be kept to a minimum in an artificial atmosphere under a bubble. Concrete dust is an inhalant hazard and very likely Lunar and Martian regolith has similar health hazards. Without roads, the humidity in the bubble's atmosphere will naturally keep the dust down to a certain extent though on heavily trafficked roads, this won't be enough. Because of the decreased gravity, the maximum size of dust particles that stay aloft for long periods will be larger than on Earth.

Asphalt and concrete as we know it on Earth won't work on Mars according to this forum thread. Basically, a lot of the ingredients that we are used to here on earth don't exist on Mars or the temperature ranges required for the terrestrial concrete curing process don't happen on Mars. A new process and new materials will need to be devised for road building on Mars.

Concrete on Luna should be possible though experimentation on actual lunar regolith will need to be done before large scale production can happen.

• "Dust of any kind will stay aloft longer on Mars and Luna than on Earth because the maximum size of a particle that falls quickly is much larger than on Earth." - I don't think that this is correct because dust needs some atmospheric pressure to be airborne. You explicitly made them in an artificial atmosphere, but if this atmosphere has a low pressure, this wouldn't mean that it will stay aloft longer. – Victor Stafusa Oct 4 '15 at 13:09
• @VictorStafusa that quote comes from the "Roads in Artificial Atmosphere" section. I agree that the explanation could be worded more clearly but the assertion is in the right place. – Green Oct 4 '15 at 13:11
• On the moon there's also no rain or frost to tear up a dirt road. Any dust kicked up quickly falls back. The two issues are not getting stuck and braking performance. – Loren Pechtel Oct 4 '15 at 23:11

As mentioned the big problem with roads on the Moon and Mars would be dust. Lunar dust is especially abrasive, since it has never been weathered, so you can imagine each speck of dust as being a razor. Over time, driving through clouds of lunar dust would be very hard on machinery.

The other issue with road building is the foundation of the road. Looking at Roman roads or modern ones you see there isn't just a layer of paving over top of the soil, but the soil has been dug down and the paving sits on top of a complex layer of engineered materials to distribute the loads of moving vehicles and maintain stability. On Earth other considerations like drainage are also in play (and if you plan to terraform Mars some day you should keep this in mind as well).

Since we are thinking in a SFNal way, one possibility to quickly build roads on the Moon and Mars would be to focus concentrated heat on the surface and literally "melt" the roads into the surface. The roads will be a sort of lava trail with the basalt forming the foundation and providing stability, while the upper surface will be a smooth layer of glass. The issue here is that the actual material of the surface is not constant throughout the length of the road, so an engineering team would pretty much have to dig a ditch and fill it with the proper materials for the basalt road before the laser or giant orbiting mirror fused it into the road you want.

Frankly, since the environments are so different from Earth, you might want to think of different methods than roads. The Moon is in a hard vacuum, so magnetically levitated "trains" might make more sense. There is no air drag, so the trains can move at hundreds of kilometres per hour without penalty. Mars has an atmosphere, so perhaps a variation of Elon Musk's Hyperloop running between Martian cities would be more beneficial for the Martian colonists.

• In a vacuum, dust does not form clouds. Dust particles fall down as fast as everything else. – Philipp Oct 4 '15 at 14:43