New Mars Forums

I've been thinking about equipping clothes only for basic vacuum safety but designing them primarily for full pressure comfortable use. In "shirt sleeve" situations a baggy garment designed to slightly inflate upon exposure to vacuum might provide good standard wear. It's not so hard to design flexible and comfortable suits that stretch out and become rigid in vacuum - your mobility is greatly limited and it's no substitute for a proper space suit but you can still move to some degree and, most critically, you don't immediately die or get limb damage if your habitat suddenly depressurises (providing a quick deployment of helmet is also possible).

SpaceNut,

Yes indeed, membrane separation is a good option if you can find the right membrane materials for the N2-Ar system, probably more scalable and far less energy intensive than alternatives. The issue is just that compression requirement, which I'd prefer to live without if possible: I want systems with basically no moving parts if I can get them, hence my preference for what amounts to pressure swing absorption even if it costs extra heat. I've seen general literature say that PSA is more expensive than membrane separation though, not sure why or how, it may be that even with a rotating compressor membranes just make more sense.

kbd512,

Tracks vs Wheels
I've seen the thread though I've not searched through the whole thing, I'm in favour of wheels for speed, simplicity and ease of maintenance. Is it really true that you get lower ground loading for a track system or is the load transmitted only to those bits of track directly beneath the driving wheels on which the tracks rest? In the case of half inflated tires pressure distributes the load evenly over the tire surface in contact with the ground, the total size of this surface is lower than for a tracked system of the same mass but I'm not certain about the load profile being spread evenly across the track because it's not transmitted by interior gas pressure (as in a wheel) but by contact with driving interior wheels. I dunno much about tracks to be honest, except that the interior driving wheels in contact with the track, being far smaller in circumference than a conventional wheeled vehicle's wheels, must have a higher rpm to get an equivalent speed to a wheeled vehicle. I don't follow the reasoning for many tracked vehicle benefits actually. That's not saying I dismiss them, this isn't my area and I'm not sure my picture of how either system works is sufficient to understand every aspect of their operation, it's just that I don't understand them working from first principles:

- Since tracked vehicles are also driven by wheels except these don't see direct contact with the ground, pushing instead on the track, I can't see why suspension requirements should be different for either vehicle if moving at the same speed. According to my picture of how these work, when going over a bump both vehicle types are inclined to move upwards over the bump to the same degree and must have a suspension of equal size to smooth out the jolt from this.

- Ground clearance seems ok to me so long as the wheels are wide apart, in fact it's preferable so that the chances of driving over a jagged rock and having it cut open the underbelly of the rover is avoided.
If it could be demonstrated that tracks can match wheels for speed, reliability, ease of manufacture and maintenance in desert conditions I'd be willing to reconsider, this isn't really my field so I'm trying to work through a lot from first principles without knowledge of direct engineering experience with either type of machine (big wheels or tracks).

I do see that tracks certainly make better use of any vulcanised silicone rubber needed for their construction: for a wheel operating perfectly, only the middle is worn down over time but the entire wheel (much of the rubber being on the sides) must be discarded once the centre breaks down. For a rubber track, being flat, the whole thing sees the ground and should hopefully be worn more evenly. A steel track (if preferable and workable) would mean saving precious rubber while a metal mesh wheel a' la the Moon landers offers very poor bounce compared to a rubber tire. As far as manufacturing expense is concerned I'll go with steel over rubber any day as long as it actually works.

Molten Salt
Now, this is intriguing but heavy. It's certainly true that molten salts can store a lot of heat (they're used on Earth) and represent a good solution for overnight stationary electric power provision at a base with big solar concentrators, perhaps competing well with batteries which at the very least require exotic chemistry if not also exotic manufacturing technology.

For a vehicle though I see many problems. A ceramic container is way too fragile for a rough off-road vehicle: sitting in front of a giant teapot full of lava and going over bumps at high speed is a no-go for me. We thus need a tough steel container, limiting our operating temperatures (hence energy density) and also meaning plenty of external rock wool insulation together with layers of reflective foil are required. I think the CO2 can be run at much lower pressure than SCO2 (supercrittical, right?) since we eventually dump it back into Martian ambient: very dense CO2 ice can be stored at 2 atmospheres and reliably outgas given sufficient warmth, going from 2 atmospheres to Martian ambient is a pressure ratio of 200, which is ample for our purposes and gentle on our machines. Heating outgassed CO2 by passing it through pipes in the molten salt container gives us a good precursor to a gas turbine. First of all though, this isn't cheap: if nothing else we need plenty of complex mechanical parts machined to high precision and plenty of high quality vacuum grade silicone lubricant. In practice many Earth-based gas turbine engines have tens of thousands of parts but even assuming we cut this down greatly they still get only around a 40% efficiency at best. Yes, true, we have a good compression ratio compared to Earth (200:1 is excellent) but the weight must be kept low and it needs to be simple so I'm reluctant to say we can do better than Earth systems in practice. That cuts down our performance a great deal. Worse, the temperature changes as our salt cools thus changing turbine characteristics. Accounting for weight of CO2, molten salt and turbines our system is pretty heavy so I dunno.

Instead, allow me to combine an idea of yours from another thread with this one:

A CO2 tank slowly lets out high pressure CO2 gas, but it's very cold at this point. It is channelled into a big trailing blimp above the rover via pipe with large spring shock absorbers along its lower length between two lengths of pipe to smooth out any jolts from the road and keep stress on the blimp low. The blimp is see-through on one side but internally silvered (using a thin coating of aluminium) on the other. By orienting it to point at the sun it focuses light onto a thin CO2 pipe through its middle and heats the CO2 from almost cryogenic temperatures up to a few hundred degrees C. Then, through another pipe flowing back down to the rover, it is channelled through a gas turbine engine and generates shaft power to drive the rover. With no molten salt and a thin blimp that lifts itself our system now has a much better power to weight ratio and much lower insulation requirements. We can use the cold CO2 gas to keep the suspension and internal systems cool, we still get a great pressure ratio because we release our exhaust CO2 to Martian ambient and you get a lot of CO2 into a low mass and volume. Mass production of liquid (or perhaps even solid) CO2 for mining equipment and so on is essential for us so this is just another application for this substance around many and can use existing supply to operate.

Being fair to this it may well give a better energy density (it's more like working gas supply but it amounts to an energy density) than batteries by far though I've not done the math properly at the moment. It's more exotic for sure and there might be problems getting our blimp to face the sun and coping with the changing power from our turbine engine that comes along with that but otherwise it might well be promising.

- Side note for molten silicon, it forms a eutectic with iron (called ferrosilicon) hence will happily eat a steel container at those temperatures! You definitely need a ceramic for that one.

SpaceNut,

I see where you're coming from but I think it's going a little too far to dismiss N2 just on one figure of merit (lifting ability) and by my analysis it certainly is a lifting gas. Let me show you my thought process:

As you say, N2 has a mass 28/44 ~ 2/3rds the mass of CO2, hence @ Acidalia Planitia's 1KPa surface pressure and air density of 0.03 kg/m^3, 100 cubic metres of enclosed N2 will lift 1 kg of blimp mass. Very true, it's not nearly as good as H2, where 100 cubic metres lifts almost 3 kg of blimp mass but it does provide lifting force and it has other advantages.

One of which is cost - I contend that it is possible to gather N2 for far lower energy expense than production of H2. As in "The Case For Mars", zeolites (basically clay boiled in sodium hydroxide, relatively easy to make) absorb CO2 very strongly when cooled and reject it again when heated. At its simplest such a system could take the form of a large fan feeding a series of pipes filled with zeolite and kept in the shade behind a large silvered curtain during the day. As the pipes cool from the shade the zeolite inside pulls air through and sequesters the CO2 component. Since the air is pushed via the fan, a mixture of N2, argon and other trace gases (whatever isn't CO2 or H2O) leaves the other side of the pipes to be collected in a balloon for later purification by compression through a membrane system.
When the zeolite is saturated one simply turns the fan off and lifts the curtain, exposing the pipes to sunlight and purging CO2 from the heated zeolite (which soaks up a lot of heat in the process). There's plenty of N2 in Mars' atmosphere.

How much heat is needed?

H2 production takes realistically something like 200 MJe per kg of H2 gas produced. By contrast, N2 production only requires heat input in the first phase and the hassle of heat rejection in the second.
For the zeolite process above, taking as a maximum energy requirement for sequestering of CO2 the latent heat of sublimation (I don't have the figures for heat released by a zeolite during absorption but it's this or lower) gives 25 KJ/mol ~ 570 KJ/Kg CO2 sequestered
(Data from eg https://en.wikipedia.org/wiki/Enthalpy_of_sublimation )

Since only 2.6% of the atmosphere is N2 we need to sequester some 60 kg of CO2 for every 1 kg of N2.
This takes ~0.57MJ/kg*60kg ~ 34 MJ of heat first rejected then added to collect 1 kg of N2 from Mars' atmosphere. The harder thing, of course, is separating N2 from argon. This could be done using a bus of membranes that allow argon through but not nitrogen or vice versa. Alternatively, there are some zeolite compositions that will soak up both nitrogen and argon but at different rates (eg https://link.springer.com/article/10.10 … 1529328878 ). Using a system like this, multiple refluxes eventually separate argon and nitrogen enough to get N2 as a lifting gas. Either way, even assuming many consecutive passes are necessary it can't possibly cost more than the heat required to sequester the CO2 in the first step so doubling that energy bill gives ~70 MJ heat for 1 kg N2 separation.

Overall: accounting for differences in density, 40 kg N2 lifts as much as 1 kg H2
40 kg N2 needs pessimistically ~ 2.8 GJ heat to produce, 1 kg H2 needs ~ 200 MJ electricity to produce
Even at its most naïve this setup makes N2 competitive with H2 as a lifting gas because heat is so much cheaper than electricity on Mars but if you treat the zeolite sequestering process as an excuse to produce high pressure CO2 and as a free heat sink you might well be producing an N2:Ar mix as a happy biproduct of what you were already doing.

As for ballast, putting balloons on the side that can be filled with CO2 does not affect buoyancy: a balloon filled with air on Earth exerts a weight exactly the same as the balloon does when uninflated (excluding the tiny amount of compression needed to fill it). An internal ballast tank filled with CO2 when you want to go down would work by displacing the interior balloon volume and hence decreasing the total lifting gas volume. By having balloons on the exterior that can be inflated when you need to go up and deflated when you need to go down you get more total potential lifting volume for your effort: they're not ballast tanks really, just extra balloons you can inflate to go higher if you need to. I call them ballast tanks simply because that name is indicative of their role. I suggest heating the interior gas using the interior swivelling cylinders silvered on one side and black on the other as illustrated, turning the black side towards the sun when you want more heat hence pressure to inflate your ballast balloons and away from the sun when you want less heat and hence for your ballast balloons to be deflated.

My main problem with H2 is its greatest strength: it's a very light molecule. It leaks through barriers very rapidly, which is a big problem if you need your airship skin to be so thin as is needed to work on Mars. It takes a lot of electricity to replace any lost H2 gas.

If we really must have better lifting performance than N2 I put methane forward as an alternative: its molecular mass of 16 means 1 kg methane displaces 44/16 ~ 3 kg CO2, hence 1 kg methane lifts ~ 2 kg of airship mass. It's even more electricity intensive than H2 to produce but at least it is bigger and hence less inclined to leak through the airship.

Interesting link for the mobile base btw, I was thinking something far bigger with almost no rigid supporting structures: only its own inflation pressure and tensile cables keeps it together, which is by far the lightest approach to airship engineering.

tahanson,

Hopefully this approach for N2 separation from the atmosphere gives ample cheap N2 for ammonia production and all the fertiliser our farmers will need!

tahanson43206,

Many thanks!

I'm not sure how I'd add in such a search tag though, looking through your most recent posts I don't recognise what they look like. Is it possible to give me a concrete example of how to make one? As in, for the above post, what tags should I use and how should they look on that post?

Thanks in advance,

Phil

SearchTerm:RoverDesign

kbd512,

In regard to trails, I think I dismissed this idea too early as requiring too much sophisticated engineering - suspension, lubrication, wheels, big motors, big batteries, etc. But I think fundamentally you're right: the cost per metre of track for a 6,000 km journey connecting, say, Elon's base idea between Amazonis and Arcadia Planitia on one end and a city state in the great drained ocean bed of Acidalia Planitia at the other so massively dwarfs the cost of a rover system as to make this viable despite the difficulties. This has the added advantage of good rover systems giving us greatly increased exploration and prospecting abilities.

To that end I've had some thoughts about how to do this. Imagine the following type of freight rover moving between "truck stop" recharge stations every few hundred kilometres.

Tires
The main consumable expenses here are in those tires. Metal plated tires, as far as I can tell, just aren't as good as silicone rubber and have great limitations on speed, wear and so on, hence silicone rubber is preferable. Silicone rubber, however, is expensive, requiring ample chloromethane and high quality ferrosilicon to produce for one thing. Worse, tires tend to get worn down so that a common estimate for our rough terrain and extreme temperature variation (at night it can drop to -80oC!) might be less than 20,000 km before changing compared to some 70,000 km for road tires on Earth (lacking better data, the general feel seems to be "it depends, be pessimistic" which is my default setting anyhow: https://www.cars.com/articles/how-long- … 668941828/ ). On the plus side there's no free oxygen in the air to break them down and silicone rubber is very resistant to UV. What's wonderful about it, however, is that it might even be possible to (after careful cleaning of a worn down tire) regrow room-temperature vulcanised silicone rubber in specialised conditions, greatly improving the economics!
Side note, lubrication in low pressures is often overlooked but critically important - NASA typically uses solids like tungsten or molybdenum disulfide which is fine for a probe but requires very rare and sought after materials. I'm not throwing tungsten away on lubricating rover axels. Silicone oils and greases, being very stable vs UV and large temperature ranges and having low vapour pressures, make excellent lubricants and can be produced using the same family of processes that make Martian vulcanised silicone rubber tires as above.

Batteries
TL;DR - We can make these in large quantities with performance similar to Tesla batteries but using only Na, C, O, H, P, Fe and other easily available Martian elements!
The situation for batteries at first sight is bleak: lithium ion is great but you have to search far and wide to get any lithium, lead-acid are easy to make but pretty terrible since they must be pressurised/kept warm as well as having a poor mass/energy density. Sodium ion batteries solve all our problems: they're almost as good as lithium ion but require only those materials present in large quantities in all Martian soil to manufacture. Anodes are fine (hard carbon can be sourced from general organic material waste), electrolytes are fine (ethylene or propylene carbonates are easy to make on site) but cathodes are a little tricky. Nickel manganese oxides, as used in lithium ion batteries, will work (but where do you get the nickel?), I tend to favour NASICON as in eg https://www.nature.com/articles/s41467-019-09170-5/

Waste Heat
Batteries and motors get hot during use and would quickly overheat without sufficient cooling. Luckily, a closed loop cycling ethylene glycol to side-mounted waste heat radiators should be sufficient to keep everything cool enough (though making such structures robust enough to survive a journey across rough terrain is something I'm still grappling with).

Electric Motors
Copper and Neodymium are not cheap or easy to mine and transport but, luckily, you can do almost as well with aluminium coils as copper and get almost as good magnets using an alloy of aluminium, nickel and cobalt (AlNiCo) with the balance being iron. Whilst we probably won't be able to manufacture anything like as good as what electric vehicles get on Earth domestic Martian electric motors and actuators are probably still good enough to get the job done even only using relatively common materials (nickel and cobalt might have to be sourced from impact craters from metallic asteroids identified by their magnetic signatures by satellite).

Now, as for electricity usage I'm not sure how to estimate this but it's likely not nearly so bad as the situation on Earth for electric vehicles - there's no appreciable aerodynamic drag and the gravity is much lower. Using as a ballpark something like this: https://insideevs.com/news/399162/scani … ks-norway/ and accounting for no air resistance and lower gravity gives maybe 500 MJe for an 80 tonne vehicle moving 100 km. Assuming sodium-ion batteries with an energy density of ~0.5 MJ/kg implies that 5 tonnes of batteries may be sufficient for 500 km range for an 80 tonne vehicle. This sounds too optimistic to me, especially since we won't have nice roads, but even 10 tonnes batteries for a 500 km trek and 80 tonnes of vehicle is pretty nice.

Overall, trails with battery powered freight rovers look like a good medium term solution for long journeys across relatively smooth terrain.

louis,

Casey Handmer is amazing but I'd like to add a technical fix to that fluorine access problem for ETFE.

The call for ETFE is based on the impression that UV damage would destroy other types of plastic which is not necessarily true - it's mostly the production of oxygen based free radicals that causes the issue (for quick reading: https://en.wikipedia.org/wiki/UV_degradation ). If you can stop oxygen from inside diffusing into the plastic then UV degradation is greatly reduced and the inclusion of hindered amine light stabilisers (HALS) as copolymers, even making up as little as 0.25% of the total plastic, this can be greatly reduced yet further.

So:
- With a thin layer of something like poly(ethyl vinyl alcohol), usually written EVOH, the majority of oxygen transmission into a plastic habitat skin can be stopped
- A small amount of HALS copolymers stops initial free radical compounds made just after UV absorption in the plastic from propagating and leads to spectacular decreases in corrosion rates before any oxygen that does get through can make things worse.

With these fixes we can just use PET or a similarly cheap and easily produced plastic with no crazy elements like fluorine needed at all.
If we reinforce with basalt fibre (very nearly as good as Keflar but far far cheaper than Keflar) instead of Keflar or equivalent we'd be able to build this sort of thing at an industrial scale using only the resources we have on hand + a few low mass imported extras like HALS copolymers, accounting for perhaps 400 tonnes of plastic per 1 tonne of HALS or something.

kbd512,

Many thanks for your praise and especially for introducing me to CNT yarn - I honestly didn't know you could do that! Having read through a few snippets on its production process it does seem quite expensive compared to alternatives but its very high thermal and electrical conductivity complete with high tensile strength to weight ratio (quite a rare combination) do open up interesting possibilities I had not previously considered. My real dream with this was to connect somewhere in the Tharsis region with somewhere further north.

Imagine Ascraeus Mons, the furthest east of that chain of three in Tharsis just before Valles Marineris, connected to a city in Acidalia Planitia. Cheap solar electricity and high temperatures from solar concentrators makes electricity, mined ores and other refined materials at Ascraeus Mons and they're shipped up to the water rich dried ocean bed of Acidalia Planitia where the main colony is based. That would be an industrial powerhouse dwarfing anything possible on Earth's Moon for instance. Alas, thousands of miles of train tracks means lots of diversions to get smooth plain over which to lay them and cablecars aren't quite what I thought they were - you're right, frozen regolith won't hold the kinds of stresses experienced by pylons (moments of force acting to topple them over, you need steel or similar for that). Perhaps a monorail could work though - there the stress on the supporting pylons is almost entirely compressive and far lower than the tension needed for a cablecar system's cable so bricks and regolith might actually do OK. It's not elegant though - lots of solar panels, lots of steel and expensive processed materials etc. If you need 3,000 km of track it will take millions of people on Mars before you could afford to build it. Stuck in one place with trade having to be done by something so inefficient as rocketry means you can't make full use of Mars' resources and have to put up with harsh compromises when picking a location of Mars to colonise. Regolith water content or sunlight? High local atmospheric pressure (immensely useful) or warm underground brine lakes and the great opportunities they represent? I want them all, which is only possible if I have cheap trade which means cheap transport. Seriously, Mars might not happen on a big scale without it.

Again, I wasn't kidding when I said this stuff keeps me up at night xD

Hi tahanson,

That sounds interesting - my mission statement is basically to make a new and technologically advanced civilisation in Space, I love the idea of having a group that works together to design stuff! Do you have an online hangout etc. for My Hacienda?

Actually, a Skype/Discord chat with anyone interested in developing technologies to make this all possible is my idea of a perfect night in, if anyone's up for this/if there's already something like this going please let me know.

(Phil)

To me, Venus is a pointless waste of resources for a colony destination this century but one of the richest and most technologically advanced places in the solar system next century when human synthetic biology becomes more ambitious. Currently, making new microorganisms means injecting small loops of DNA (plasmids) to make single enzymes to do simple chemistry tricks but technologies like CRISPR (eg https://en.wikipedia.org/wiki/CRISPR ) might well change all that, permitting the editing of DNA for fully developed multicellular organisms. There's no fundamental law in physics that says you can't make a capsule the size of an acorn that, planted in Mars' soil and left for a century, turns the entire surface into a sprawling cityscape enclosing millions of square kilometres of forest and high technology. The right strings of DNA in the right tiny organisms ought to be able to hold many times the information required for this - Human DNA, after all, contains all the information required to make one of us in only 3 billion base pairs. Of course, the engineering problem of designing such an acorn and in particular the algorithm that must run going something like "if I wanted this structural shape and properties, what DNA pattern would I need?" is so laughably impossible for us that I can't find any biologists who've even considered it seriously before. They should. At least, I think they should. Printing and reading DNA is getting cheaper and cheaper, molecular chemistry more and more sophisticated. The technology to try things like this and the computing power required to predict which sequences of DNA you need for your intended tasks may eventually come into our hands. Well, maybe our descendants' hands.

Nonetheless, long before anything that ambitious there are many potentially world-ending organisms that would have to be tried and tested. Never mind the conspiracy theories that say COVID-19 escaped from a lab, even if untrue it certainly could have been true. Searching for the cures to all human disease (the tip of the iceberg of what is possible for biotechnology) requires extremely dangerous research. This should not be done on Earth. Hence where Venus cloud cities come in. It provides an environment in which:

- All the bulk materials for life are available in abundance.
- Vast habitat volumes are cheap to build and maintain.
- Conditions outside are extremely hostile to life (that is sulphur dioxide, sulphuric acid, hydrochloric acid, harsh UV etc.) so that anything that got out by accident would quickly die off (and there's no good reason to breed organisms resistant to these conditions!).
- The gravity well is quite steep so that it's difficult for any escaped organisms to find their way out into the solar system even if they could survive.
- A rapid self-destruct mechanism exists for all cloud habitats: you vent the internal air and rapidly decend into the hellish conditions of the lower Venusian atmosphere, very definitely sterilising all biological entities onboard in the process.
- Launching from the planet is difficult so that even if pirates or agents of some nefarious organisation were to try stealing COV-AIDS or whatever is being tested and you couldn't self destruct in time it would be difficult for them to get physical samples off world.

Venus, as I see it, is analogous to the perfect playground for toddler Clark Kent to get comfortable with his own limitless powers without the threat of accidentally blowing up all of Smallville when he tries his laser eyes for the first time without appreciating exactly what that does.
Needless to say, the power of the advances that might be made if only experiments with biotechnology could be performed safely while our wisdom on the subject grows could be extraordinary. Medicine is already a multi trillion Dollar field, even if it stops at permitting people like the late Robert Bussard or Freeman Dyson to continue working for more than a poultry 50 years of career before leaving us forever (I'm massively pro cryonics as a short term solution to this) I imagine the monetary gains for humanity would dwarf the entire world economy as it exists today. Hence why I see Venus as the Silicon Valley of the next century and synthetic biologists as the new programmers and consumer electronics designers, filled with high-tech floating laboratories manufactured in Martian orbit for use there. Not today though. Mars is just so much better a colony destination as a whole package, in fact it can certainly provide reasonable isolation and security for biotech firms, perhaps even good enough that the advantages in my list that Mars doesn't have aren't worth the extra hassles that come with colonising Venus in the first place. I dunno. This is how I see it anyway.

Now, overall I envisage something like the following:

The hanging weights at either end of a length of cable provide cable tension to counter sagging as a cablecar passes between two pylon supports, probably just a big mass of regolith piled into a bucket attached to the cable.
The pylons themselves are built from frozen regolith melted under a moving dome as mud and piled up before being left to freeze again as per a previous post. In normal operation the tension in cable either side of a pylon cancels out and the pylon is fine. However, if a cable snaps the neighbouring pylon has to suddenly take a large force acting from the adjacent cable attached to it that is unbroken. If it can't stand up to that, the pylon will collapse, putting a similar stress situation on the next pylon along, which also collapses...

...And a few hundred broken pylons and snapped cables later I get fired, never to work in the Martian transport industry again.

To avoid this fate such a design must have some combination of:

- Nice thick frozen regolith pylons, perhaps reinforced with regolith brick or steel rebar but those are pricey
- Closely spaced pylons
- Lightweight cablecars
- Lots of sagging that we just live with

Of the four, the last one offers the best cost savings, though it does mean that the tensioning weights have to move substantially every time a cablecar passes through. Friction between the weights and the pylons from which they hang is something I've yet to figure out and it's probably quite serious at night when everything gets cold and brittle (yes, cold steel cables is probably very bad, will discuss below). A pulley system might work well, giving lots of extra slack for the cable to sag for only modest movement up and then down again of the tensioning weights but I'm not sure yet.
The easiest fixes therefore are the other 3, though they're unattractive because they mean less freight per unit time for the same infrastructure cost!

I dunno. It's not without difficulties but if one could figure them out it might be very competitive. Getting practical local transport on Mars keeps me up at night.

On the bright side, if heating steel cables by using them to transfer power to a cablecar is impractical (I don't want to pay electricity for anything like that if I can afford it, electricity is a precious commodity on Mars), it might make sense to use another kind of cable entirely.  Basalt fibres are very strong, lightweight, and easy to make in large quantities. I know that magnesium alloys actually get much better at cryogenic temperatures (at least according to Dieringa: https://www.researchgate.net/publicatio … s_A_Review ). This is no good for a conductor because alloys are always worse electrical conductors than their pure metals but if this holds true also for pure magnesium or aluminium (or at least that they don't become unacceptably brittle) then we could use reinforced magnesium or aluminium cable and transfer power for the cablecar through it as well! Pure magnesium is a slightly worse conductor than aluminium but it's less dense such that the same weight of cable can carry about the same current with the same low thermal losses so both are possible and both are present in large amounts in all Martian soil. If you have a non loadbearing cable overhead of Al or Mg and a boom that makes contact between your cablecar and this cable you can pass a current through the overhead power cable, to the cablecar and away through the loadbearing basalt fibre reinforced lower cable and to ground.

I dunno. If I get accepted into the finals for this year's Mars colony competition then I've got to include something juicy for Mars intercity transportation at the Mars Society convention or else it's a massive problem for any long term colony efforts that just hasn't got any good solutions atm.