Surface Freight Transport on Mars

I have seen many notions for surface transport discussed on the New Mars forums,  mostly in the planetary transportation topic.  Nearly all of these suffer from the very serious downside of requiring the emplacement of significant infrastructure on Mars,  something very effort-intensive and very expensive,  here on Earth.  With transport costs to Mars being “astronomical” for the foreseeable future,  that is a fatal requirement for anything we might consider on Mars.

What one really needs to do first is determine a very fundamental characteristic:  is the cargo time-sensitive,  or is it not?  Transport of people over long distances is a very time-sensitive problem,  for which the solution is some sort of flight,  as Figure 1 suggests.  Most bulk freight is not time-sensitive at all,  and can travel very slowly,  similar to scheduled rail freight here on Earth.  Considering the expensive infrastructure issue,  what we need is a train that does not need any tracks. 

That small portion of freight to be transported that is time-sensitive is likely to be medicines and similar:  small packages that can fly with the people.

Figure 1 – Time-Insensitive Freight Should Go Slow,  On The Surface

The critical thing here is to minimize the infrastructure we must emplace to get any of these transportation ideas going.  The more you have to build,  the more it is going to cost,  for both the efforts,  and the materials,  plus the equipment with which to build it.  That’s true here on Earth,  which is why many of these ideas have never really been widely built,  even here.  On Mars,  it will cost a lot more still,  because of the interplanetary transport costs,  plus the development costs of re-making the materials and processes into those that will actually work on Mars.  As indicated in Figure 2,  about the only thing we have available that would actually work on Mars,  too,  would be graded dirt roads,  with “truck trains” moving on them.  True rail would cost less to run,  being lower friction,  but we have no way to manufacture steels on Mars,  including the extreme-cold adapted steels necessary there,  and no way to make the ties,  whether from steel,  concrete,  or wood.

Figure 2 – The Real Requirement is That There Be Almost No Infrastructure to Emplace

So,  it is the slow-moving “truck train” hauling the time-insensitive freight on graded dirt roads that we need for Mars.  This is really just a tractor pulling a string of freight wagons,  but internal combustion engines as we know them here on Earth are “right out”.  You not only have to carry the fuel,  but also the oxygen with which to burn it,  which considerably outweighs the fuel.  And unless you want to completely redesign the engines to handle 500-1000 C higher flame temperatures,  you will also have to carry diluent gas,  which in turn far outweighs the oxygen.  So,  in any practical sense,  you are looking at electric-powered tractors.

These can be solar electric powered,  however.  On a sunny day here on Earth at lower latitudes,  there is roughly a horsepower’s worth of energy per square yard falling on the ground.  At Mars,  there is about half that.  Call it 300 W per square meter as a rule-of-thumb.  Solar electric conversion efficiencies are around 20%,  so about 60 W per square meter of collector surface could be had,  for much of the day.  The trick is then to fit the freight wagons with solar panels on their roofs,  all connected electrically to power the tractor.  You just go very slow to stay within the power your solar collectors can generate.  But,  most bulk freight is very time-insensitive,  so who cares?

This thing doesn’t need a crew,  it can be self-driving between the spoil berms created from grading the road.  If programmed with a keep-right feature,  traffic on these roads can be two-way.  The basic characteristics and features are summarized in Figures 3 and 4. 

Figure 3 – The “Truck Train” Concept

Figure 4 – This Is How It Is Controlled

Now we need to verify feasibility with some numbers.  Trucks and train cars here on Earth are about 1/3 structure and 2/3 payload,  sometimes ¼-3/4.  Call it 30-70,  as a rule of thumb.  For a 100 metric ton loaded freight wagon,  you are looking at 70 tons of payload,  and 30 tons of chassis,  wheels,  drawbars,  containing-structure for the freight,  and solar panels on the roof. 

These things could use the very same giant rubber tires we use for off-road construction and mining work here on Earth,  but we may need to heat them slightly,  to prevent their cracking in the cold on Mars.  That can be done.  Tires on relatively smooth,  firm dirt have crudely 10 times the friction coefficient of tires on a paved road.  Using the Mars weight of a 100-ton loaded freight wagon,  augmented for climbing a 10% grade,  the drawbar power (drag x speed) is 20 KW at 0.33 m/s,  and quite a bit higher as you go faster.  There’s room for at least around 300-ish square meters of collectors atop each wagon.  Which in turn is why you select the lower of the speeds given in Figure 5.  

Figure 5 – This Is Why It Works (By the Numbers)

You can pull many freight wagons with a big powerful tractor.  Numbers are given in the figure for 10 and 100 wagons.  Power at the tractor is between 0.2 to 2 MW for these numbers.  That’s about like the power of a big mine loader as currently built here on Earth (somewhere near 1000 HP).  Which in turn means the same electric tractor that can pull the “truck train” can also be the road grader! You just power it differently.

The kind of thing I have in mind as the basis for designing the Mars tractor is pictured in Figure 6.  That is a big mine loader vehicle.  These are very tough,  very powerful machines.  That is the very thing we need for doing road grading,  and pulling heavy trains of freight wagons.  We just have to make it work on Mars,  in the cold and the near-vacuum.  That is why electric propulsion is preferred,  and a pressurized operator’s cabin is required. 

Figure 6 – The Mars Tractor Is a Known Revision of Something Like This That We Already Build

The basic notion is illustrated in Figure 7.  Something similar to a big mine loader is the design basis.  You remove the dump hopper and replace it with a battery bank and solar panels.  You remove the diesel power plant and replace it with the appropriate electric drive motors and gearing.   You replace the operator cab with a pressurized operator’s cabin for use on Mars. 

Rigged with a blade,  and powered by a nuclear generator aboard a shielded trailer,  you operate it manned for grading the road.  Unmanned and self-driving,  you pull the “truck train” with it,  powered by the solar panels on the freight wagons.

It will have to be manned for grading the road.  Even here on Earth,  “dirt work” is something that has so far proven to be not-automatable,  or it already would have been automated.  That’s slow multi-pass work,  with the operator’s judgement and skill showing up,  as knowing when the work is done “right” by the appearance of what he has done.  This aspect will be the same on Mars as it is here.

It does not have to be manned to pull the “truck train” on the finished roadway.  You remove the blade,  and delete the nuclear power trailer.  However,  I would leave the pressurized cabin in place and rigged with supplies,  for the off-chance unforeseen event that would require a human driver.  

Figure 7 – Converting a Mine Loader Design into a Mars Tractor Design That Does Two Jobs

The only real trouble is shipping such large pieces of equipment to Mars.  These will have to be shipped as individual components,  and assembled there on the planet Mars. That will be true until some very large interplanetary vehicles indeed,  eventually become available.  But it can be done,  with what we know and have available,  right now!