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#176 2020-07-29 13:02:40

tahanson43206
Member
Registered: 2018-04-27
Posts: 3,074

Re: Trains on Mars - Could a rail system provide martian need

With any luck, the link below will bring up a "sketch" of what I understand to be SeaDragon's idea, as modified by suggestions from kbd512 and Calliban, but without all the features added in recent posts.

What I was hoping to show here is the principle of the suspension bridge concept of dropping lines from a catenary curve to provide an even "platform".


EIhFH7K.jpg

The sketch is done with the mouse, and the lack of autosnap lines is an issue, but hopefully the wavy lines will suffice.

(th)

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#177 2020-07-29 16:42:23

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,200

Re: Trains on Mars - Could a rail system provide martian need

The mounds could be microwave arc weld to make them more structurally harder to support the mass of the system and payload.

by the way nice sketches.

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#178 2020-08-01 05:27:35

SeaDragon
Member
From: Merry Old England
Registered: 2020-07-25
Posts: 16

Re: Trains on Mars - Could a rail system provide martian need

tahanson,

So with suspension cables as illustrated in your post (which is perfectly visible and clear by the way, I say we all need to do more sketches!) it doesn't really fix the problem:

hXbJdUT.jpg

On the lefthand side I've drawn the situation on the main horizontal cable when the cablecar is between the pylon and first cable, it's the same problem between any of them: unless the cable sags (and only to the extent that it sags) the cable can't provide an upward pointing force to resist gravity and the cablecar falls to the ground. What you actually get is closer to the image on the right - sagging there does get you a vertical component and it is kept up and the overall sagging is less than with no suspension bridge supports of the type you drew. The problem with this is what happens at the towers where the suspension cables are attached: there's now a huge force moment pulling the second tower towards the left of the screen. You can make towers that resist this kind of force but not out of brick or regolith because bending moments in a vertical pylon require both tensile and compressive strength to resist: such towers require lots of steel and heavy engineering.

What I wanted with cablecars was a way to move cargo with only the bare minimum of processed material needed (a thin cable and some small steel connectors at the top of regolith pylons). Regolith and brick are weak and you need a lot but it's orders of magnitude easier to pile up or bake local dirt than to produce complex steel supports and move them hundreds of miles across the Martian landscape (tragically it's difficult to move heavy beams by the cablecar network you just built!).

The other problem of course is that you need uninterupted cable or else the cablecar can't have a gripping arm attached to that cable - what do you do when you find a supporting cable sticking out of it? You can't let go and reattach on the other side because you'll fall off, having several grips that let go and reattach in sequence to get past an attached cable are way too slow and complicated.

Because the tensioning of a cablecar track requires bending stresses in pylons (hence serious materials like steel) I think unfortunately the cablecar concept isn't that practical.

A monorail, however, might actually be competitive with traditional tracks!

Even there, suspension has its problems:

3g3UU69.jpg

With a suspension bridge you're trading a thinner and lower stressed rail for a big steel tower to which your cables must be attached. That's maybe a good idea, maybe not, honestly I'm not a civil engineer so this is a bit outside my experience. Still, you live and learn I guess. I'd honestly thought I was onto something good with a cablecar network, the problem of transport on Mars (which is very serious) is thus yet unanswered. I'll keep trying until it gets done.

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#179 2020-08-01 05:44:47

SeaDragon
Member
From: Merry Old England
Registered: 2020-07-25
Posts: 16

Re: Trains on Mars - Could a rail system provide martian need

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

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#180 2020-08-01 06:13:29

tahanson43206
Member
Registered: 2018-04-27
Posts: 3,074

Re: Trains on Mars - Could a rail system provide martian need

For SeaDragon re #178

Bravo!  Good points, well made.

However, I hope you will not give up so quickly on an idea that has some significant potential.

It is clear that even having drawings does not (in itself) overcome the problems of communication, but it ** does ** substantially improve the turnaround time.

Your point about lateral forces on the frozen regolith is a good one, and it deserves a suitable response.  A frozen cone of regolith needs to be free of lateral force altogether, and fortunately that can be obtained.

Your concern about dropping of elevation in a horizontal run supported by a set of suspension elements from a catenary cable seems reflective of the fact we are (apparently) both approaching this concept for the first time.  I am reasonably sure a ** real ** civil engineer would be able to reassure readers of this forum that a well designed suspension cable system will ** not ** suffer from a rolling depression of the road surface.   However, I am guessing that our hypothetical engineer would suggest including some resistance to vertical distortion in the "roadway", and the result would be increased mass for the girder structure that would be required.  In other words, I agree that ** some ** mass would have to be allocated to the "roadway" to insure it does not flex during use.

However, I would like to introduce a hybrid extension of your concept by adding some (or at least one) idea from kbd512's long set of posts about a wide variety of subjects.

I'd like to invite consideration of changing your concept so it supports a high voltage cable that can be accessed by arrangements similar to the "trolley" car systems that existed on Earth for an extended period, in a number of cities.

SpaceNut, could/would you be willing to find some images of trolley car systems?  The details I am looking for are suspension methods.

The contribution I ** think ** I am remembering from kbd512's many posts is the idea of a land vehicle (probably a tracked one put possibly wheeled) able to pull power from along the roadway.  In the case of the trolley-like overhead power cable, there would be no tracks, and the vehicle would move on the terrain, which would become packed with use. 

(th)

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#181 2020-08-01 08:54:33

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,200

Re: Trains on Mars - Could a rail system provide martian need

Louis presented the power road some time ago. It would work in a simular fashion to the wireless cellphone charger.

The CNT cable would need the same insulators as our power lines use on the telephone power poles do.

1024px-2013-cable-trolley-power-line-maintenance-1.jpg

9223-004-B67F17D4.jpg


9b320c5bb3353d541970ef1462b371ae.jpg

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#182 2020-08-02 17:22:25

kbd512
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Registered: 2015-01-02
Posts: 3,561

Re: Trains on Mars - Could a rail system provide martian need

SeaDragon,

I'm not sure if anything sent to or built on Mars will be cheap, but there are certainly lots of ways to make it more expensive or less efficient than it otherwise could be.  To be perfectly honest, I think it would be easier to bulldoze a trail, a rudimentary road cleared of large rocks that could damage the drive train of heavy off-road vehicles, than it would any other type of structure for mass transport of goods over long distances.  It wouldn't be as efficient as a cable car or train or real roadway, but the raw materials required are virtually nil and the infrastructure to supply those materials, also nil.  No matter the solution, there would have to be an overriding requirement for mass transport of materials over long distances, generally dictated by the number of people supplied with those resources.  If you find a healthy supply of water and industrial chemicals or construction materials in one area, odds are pretty good that that's where a settlement would be established, just as they were here on Earth.  The entire purpose behind an overland exploration campaign would be to establish "ground truth", as GW calls it, to determine where the best sources for specific natural resources are located.  Placing your settlement in close proximity to natural resources lessens the requirement for sophisticated long distance transportation infrastructure such as trains.

The "ground truth" estimates from the various probes and rovers sent to Mars is that the entire surface is covered with multiple meters of very fine dust before you hit bedrock.  Naturally, that varies wherever you go and there are also larger bits of rock mixed in with the dust, which NASA's InSight mission discovered.  Could you dig down to bedrock to build a permanent foundation for a train or trolley system?  Sure, but you're talking about moving massive quantities of materials to do that over any significant distance and the power requirements associated with doing that are pretty extreme.  There's a reason we have diesel-powered construction equipment, rather than solar-powered construction equipment, here on Earth.  Furthermore, construction is not automated.  Even if you see a robot working on a construction project, you inevitably see at least one human attendant standing right next to it, feeding materials to it or cleaning it or repairing it, as required.  We have numerous construction and mining machines that do the work of many men, but those machines are truly massive, require lots of power, and depend upon a very healthy supply system to repair or replace broken parts.

Between now and whenever Mars eventually has millions of colonists living on it to justify the expense of a railway or roadway system, either a trail or that cable car system seems like one of the least resource-intensive, therefore costly, ways to transport many tons of materials to wherever they'll be processed.  Starting from zero will never be cheap and easy, but whatever solution is the most efficient will win on Mars due to cost.  In the shipping business, that translates directly to weight (therefore power requirements) and maintenance.  The system that requires the least amount of power and maintenance will win, unless other considerations such as speed-of-service are more important (the only reason we still have air mail here on Earth).

If we devised a land system with a transport speed of 200mph here on Earth, most shipping companies would drop in-continent air mail on cost grounds and speed-of-service.  Actual testing has shown that if you can develop a light aircraft that goes at least 200mph, then most of the time it will beat an airliner between any two points in the continental US as a function of airport wait times and other hassles associated with proximity to your final destination, despite the fact that the airliner can theoretically travel at 600mph (theory vs practice).

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#183 2020-08-03 13:48:15

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Trains on Mars - Could a rail system provide martian need

A tractor cab (electric powered?) could pull a semi-trailer plus a trailer or two,  on a graded roadway,  at modest speeds (~ 30 mph).  With air-breathing diesel,  this is already done routinely in Australia at full speeds (30-70 mph,  depending upon the roadway surface).  You just can't use diesel on Mars because the air is too thin and there is no oxygen.

But you do have the rooflines of the semi trailer and all the trailers on which to mount solar arrays.  And you can make local water into compressed gaseous hydrogen and oxygen for a fuel cell rig and tanks in the tractor cab. Just think of it as an electric train that needs no tracks,  only a graded road.

Later,  when there are tracks or well-paved roads,  you can up the power and drive this train faster.

GW

Last edited by GW Johnson (2020-08-03 13:50:14)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#184 2020-08-06 01:57:29

kbd512
Administrator
Registered: 2015-01-02
Posts: 3,561

Re: Trains on Mars - Could a rail system provide martian need

GW,

I've taken a second look at using Strontium-90 for in-space and surface power applications, mostly using direct thermal power supplied to advanced supercritical CO2 turbines.  Sr90 may be less desirable compared to Pu238, but it's very plentiful compared to Pu238 and much cheaper.  We also have many thousands of tons of the stuff since it's a daughter product of fission.  We'd need 5,435kg of Sr90 to produce 2.5MWt at BOL and 1.5MWt after 20 years of service.  I estimate the radiator mass at 500kg or less, though even if that was doubled it wouldn't be a major problem.  I was also thinking that at least part of the radiator mass could be supported by the sides of the gondola to keep the CG as low as possible.  The SNAP-50 reactor design of the 1960's was to dissipate a 1,448kWt thermal load at 1156F using 1,100 pounds of 316 SS tubing and Copper fin radiator and that radiator design was 700ft^2 (from the boiling Potassium reactor design Calliban pointed out).  I believe that was single-sided, as it would be in this application, although I could be wrong about that.

Some of the radiator mass would be integrated with the vehicle mass.

Sr90 Characteristics:
Density: 2.375g/cm^3 near the melting point
Half Life: 28.1 years
BOL Thermal Power Output: 460W/kg
BOL Surface Temperature: 700C to 800C

Pu238 Characteristics:
Density: 19.329g/cm^3
Half Life: 87 years
BOL Thermal Power Output: 540W/kg
BOL Surface Temperature: 1050C

Anyway, the idea is that the RTG and radiator mass is split between two tracked prime movers, so each tracked prime mover nominally produces 1MWe at BOL or 750kWe at EOL, one at the front and one at the end of an overland version of a railway boxcar.  The primary construction material for the prime movers would be the 5083 Aluminum alloy used by the M113 APC, along with forged steel track links and Thoraeus metallic rubber clad road wheels to better withstand low temperatures.  The vehicle design will be similar to the Swedish Stridsvagn Strv-103, meaning it will use hydraulic suspension to increase ground clearance for travel and to "kneel" when not in operation to better facilitate loading / unloading operations.  If you google, "E-10 Jagdpanzer", visualize this vehicle without a gun and a giant articulating hitch on top to support one end of an Aluminum railway gondola car and that's pretty much what I had in mind.  I figure we'll use the T157 track shoe for ease of disassembly with a speed wrench, despite it's weight per foot (71.4 pounds per foot).  It's reasonably stout, 21 inches wide, and used on the M2 Bradley IFV- a vehicle in the same tonnage range as the load we're trying to support on Mars.

We're going to stipulate that each prime mover weighs 12t, even with the mass of the RTG and gas turbine, since each prime mover will be a single seat vehicle with limited interior volume.  The SCO2 turbine will provide direct mechanical power to an automatic transmission.  For reliability, a miniature thermoelectric RTG will supply electrical power to onboard vehicle electronics and life support equipment.  A hydraulic pump will be attached to the gas turbine's accessory case to supply hydraulic power for the articulating suspension and for mounting / dismounting the Aluminum gondola at the mine and ore refining facility.

A BNSF aluminum rotary gondola railcar weighs 41,900 lbs / 19,045kg empty and its load limit on a railway is 244,100 lbs / 110,955kg.  This type of railcar is used for transport of metal ores.  We're going to stipulate that the weight of the steel trucks required for railway use will be replaced with structural reinforcement of the car for overland operations and a pair of articulating "trailer hitch" type structures to connect the gondola to the pair of prime movers.  The total mass is 154,000kg on Earth and 58,520kg on Mars.

The complete vehicle with max payload weighs 128,978lbs on Mars, for 20.8hp/ton, when loaded like a train railcar.  That's slightly better than the British Challenger 2 MBT, supplied with 19.2hp/ton via its 1,200hp Perkins diesel.  Maximum off-road speed for Challenger 2 is 40km/h, so I expect that over a graded trail, this vehicle could manage the same speed.

That's a heck of a lot more mass and power to move this vehicle acceptably well over an off-road environment than a standard railcar requires by rail, but it should still work.  Since there probably won't be any paved roads or trains on Mars for quite some time, this solution still permits transport of 110t railcar load using roughly the same transport technology we use here on Earth in mining operations.

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