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#126 2018-09-13 05:04:20

elderflower
Member
Registered: 2016-06-19
Posts: 929

Re: Mars Cart

A radio isotope heat source could be used as filling fluid in a pretty much conventional tire. Polonium 209 (half life is 130 years) in solution in water/antifreeze might be suitable. Polonium is quite volatile so spills would dissipate, and is an alpha emitter so significant radiation would not escape from the tire interior absent a spill.Water filling of tires is used on earth for better traction and to add weight to the machines that are used to settle landfills.

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#127 2018-09-13 09:56:42

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,231
Website

Re: Mars Cart

Liquid-filled tires?  Try just using silicone oil instead of radioactively-heated water.  Don't need the radioactives.  I found one good just past -100 F (-73 C) a few years ago.  Viscosity was about that of aircraft hydraulic fluids,  even cold.  Rubber tires have indeed been used at South Pole station,  during the 1957-1958 IGY. There should still be a rubber that would work in the cold on Mars. 

But,  why not just do what worked on the moon?  Rocks and harsh dust there,  too.  And cold in the shadows.  They used steel. 

I do have a problem proposing internal combustion engines for use on Mars.  Three,  actually. 

First:  None of our fuels burn with CO2.  They burn with air,  and too hotly with straight oxygen.  You'll have to carry oxygen,  and either carry or compress CO2 as a diluent gas.  The stoichiometric air/fuel ratio here for all our practical fuels falls near 14-15.  Your oxidizer tank and equipment is going to utterly dwarf your fuel tank. 

Second:  compressing CO2 from 6-8 mbar to multiple bars is NOTHING AT ALL like compressing from near 1 bar to multiple bars.  The compression equipment is NOTHING AT ALL like the kind of compressor you can buy at the store.  It's going to be too big and too heavy,  and supply far too little compressed mass rate to be practical.

Third:  you must operate your internal combustion engine with an intake pressure near 1 bar,  so that in-cylinder compression pressure is multiple bars,  and combusted pressures are a few dozen bar.  Otherwise,  you don't get any power out of the equipment for its weight.  Basic thermodynamics and thermochemistry tell you that.  Which means you WILL have carry or compress a diluent gas,  in addition to compressed or liquid oxygen. 

All in all,  I really think your rover cars,  road graders,  and bulldozers are going to be rechargeable battery electric,  on Mars.  The construction equipment might use the electric motor to power a hydraulic pump for hydraulic drive as well as hydraulic device actuation,  but electrically-driven that pump will be.  That is something we already know know to do.  It is light enough to serve as it is. 

There are no ready solutions for the other. 

GW

Last edited by GW Johnson (2018-09-13 10:01:14)


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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#128 2018-09-13 10:17:16

kbd512
Member
Registered: 2015-01-02
Posts: 2,113

Re: Mars Cart

I'm all in favor of battery-powered and steel-tracked vehicles.  Unfortunately, there are a lot of people out there who think trucks are ideal for off-road use because they've never seen the broken axles, diffs, and punctured tires associated with operating a heavily laden truck in rough terrain.

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#129 2018-09-13 10:40:24

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,231
Website

Re: Mars Cart

Well,  it depends on how tough the terrain is.  Lots of construction equipment uses wheels,  some use tracks. 

I once had to lay a water main 6 feet down in monolithic limestone.  Code requirement for a fire line.  Backhoe was ineffective.  We rented a track hoe,  which was heavy enough to do the dig. We welded a lot of teeth back on that bucket,  but it did dig solid rock.  All the backhoe could do was make small amounts of rock dust.  Wasn't the tracks,  it was just the weight we could bring to bear on the bucket. 

I think Mars rovers will resemble construction equipment more than trucks.  The terrain is too rough for anything less durable than construction equipment. 

All in all,  I think we quite agree.

GW

Last edited by GW Johnson (2018-09-13 10:41:54)


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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#130 2018-09-13 11:43:22

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,548

Re: Mars Cart

On other threads, some have suggested simply attaching blades to the rover vehicles. What will this actually accomplish? Nothing, other than to wreck the rovers, and be ineffectual construction equipment. My latest "hot flash" of an idea is to build the construction equipment modularly, with quick-change battery trailers. Use apparatus until a yellow warning light comes on--drive to battery trailer depot--attach new battery trailer and continue working. Vehicle itself also has battery which can serve should trailer reach power exhaustion before reaching change station. These could also be "drop in modules" which in case of a Bobcat type loader, serve as vehicle tip-over counterweights.

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#131 2018-09-13 11:49:11

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,548

Re: Mars Cart

I also agree that steel-tracked vehicles are far more capable and durable than wheeled trucks. Offsetting this notion, however, is the inordinate amount of daily maintenance required to keep them operational. In general, based on the duties of some of the armored crewmen I knew operating M-60 tanks in Germany during the 1960's, they stated it took roughly 8-9 hours of maintenance for every hour of operation. Mostly on the drive train, but focused on the track wear.

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#132 2018-09-13 15:37:02

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,231
Website

Re: Mars Cart

If it's rough enough,  that justifies tracks.  The wheeled construction equipment has huge wheels with extremely-tough,  gigantic tires.  That usually survives off-road pretty good.  What I am talking about is not just a different class from what goes on a big rig highway freight truck,  it's virtually on a different planet.  I'm talking about the kind of wheels you see on a road grader.  Or bigger.

Now there ought to be a rubber that will withstand the cold on Mars without being brittle.  If the rubber tires work,  you can use silicone liquid fill inside them as ballast.  But if not,  just do the steel tires that we did on the lunar rover car,  just a whole lot larger.  And thicker.  And add a ballast container on the bottom of the vehicle:  put regolith in it.

I honestly don't understand why these KISS concepts seem elude so many.  Have none of you ever worked on real construction sites at the dirt-work stage?  I have.  I thought many did (guess I was wrong).  There's nothing at all hard about this,  except the mass and the price tag. 

Oldfart's battery trailer is a good idea,  by the way.  Maybe not for diggers,  but some dozers and most graders might benefit.  Certainly the equivalent of a dump truck would benefit. 

GW

Last edited by GW Johnson (2018-09-13 15:39:11)


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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#133 2018-09-13 17:23:43

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 13,056

Re: Mars Cart

SpaceNut wrote:

I was wondering if we could design a near diesel engine with fuel supply injectors using hydrogel fuels?

Granted it would be better not to need to take this fuel with us but in the future I would hope that we could make it insitu.

Then the solar panels would be to power the general lifesupport and other needs for such a rover.

GW do you think that a newly designed engine using the hydrogel fuels would work when using the air intake as a temperature moderator for the chamber control and as a working fluid as it pumped internal to the engine to remove heat. Feed the exhaust into cool storage to recycle the output.

Here is a simple view of all the other considerations that we would make in the design of a vehicle for mars.
https://www.buildyourownracecar.com/rac … nd-design/

This was my image search for suspense and framing for the pedal powered hybrid that I am thinking of building for at least short hauls.


https://web.wpi.edu/Pubs/E-project/Avai … _Paper.pdf

https://hobbylark.com/misc/Build-Your-O … Step-Guide

https://www.motherearthnews.com/diy/diy … az83mjzraw

https://www.mfgsupply.com/gomini.html

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#134 2018-09-14 04:00:32

elderflower
Member
Registered: 2016-06-19
Posts: 929

Re: Mars Cart

If you must have a heat engine, why not just use a gas turbine, without the compressor and with multiple stages, ultimately exhausting to atmosphere. Flame temperature can be moderated by injection of bottled CO2 or water from a tank, allowing use of relatively cheap materials.  Without an attached atmospheric compressor this device could be remarkably efficient in terms of specific fuel consumption, so could be made very small. It might not be ideal for powering a large machine all day, but for getting you home with a flat battery....

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#135 2018-09-14 07:01:41

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,939

Re: Mars Cart

For a given amount of energy use, would a vehicle go further or less far in the 0.38 G conditions on Mars?   Obviously friction would be less, or I presume that's the case. But I read elsewhere (maybe here) that a wheel moves because of the reciprocal force from the ground (which suggests that force might be lower in lower G, but I've no idea).


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#136 2018-09-14 09:02:50

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,548

Re: Mars Cart

Power is defined as work accomplished per unit of time. Work is defined as moving (or lifting) a defined weight (mass x gravitational constant) a defined distance against the gravitational field. So...total energy expended is defined by the power times time. Basic physics should provide your answer. So, on Mar, a defined amount of energy would accomplish the identical amount of WORK as on Earth, but by moving more MASS as a result.

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#137 2018-09-14 10:59:41

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,231
Website

Re: Mars Cart

For a surface vehicle,  travel is steady state when thrust equals total drag.  Air drag on Mars is unimportant.  Rolling drag is what you must overcome,  plus vector weight components when not on level ground.  The rolling drag is a friction coefficient-like coefficient multiplying the normal force (which is the weight on level ground). 

For steel wheel rolling on steel rail,  that coefficient is on the order of 0.003.  For rubber tires rolling on hard but smooth (!!!)  pavement,  that coefficient is near 0.015,  maybe twice that if not so smooth.  For pretty much any sort of wheel running off-road on hard (!!!) ground,  that coefficient gets quite large,  as in maybe the 0.1-0.3 range.  Make the ground soft,  and it’s up to around 10 times larger still. 

Ugly little facts of life,  but there it is.  The actual friction forces on a given mass vehicle are lower on Mars because of the lower gravity,  yes.  These lower the power you must have (drag x speed = power,  with consistent units). 

But all the ground on Mars is “off road”,  much of it is sloped greatly,  and quite a lot of it is soft sand with sharp rocks in it.  Your frictions will still be very high,  and you will face vector weight components at 30+ degrees quite often.   Maybe 45+ degrees crossing gullies.  I’ve driven slopes like that on the river roads in Big Bend National Park.

GW


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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#138 2018-09-14 14:42:54

kbd512
Member
Registered: 2015-01-02
Posts: 2,113

Re: Mars Cart

Louis,

Some of us favor using an all-electric system to negate the issues with storing volatiles aboard pressurized vehicles and the mechanical reliability of virtually any electric motor when compared to virtually any piston or gas turbine combustion engine.  With proper power regulation, it's not even a contest.  The electric motor wins every time.  The power-to-weight ratio and efficiency of modern and inexpensive axial flux permanent magnet electric motors greatly exceeds the largest and most efficient gas turbines in existence.  When money is no object and there's no air resistance to speak of, you can hoist a large thin film sail from the top of your tracked armored personnel carrier and soak up as many trons as you need to provide adequate power.  Electric motors provide gobs of torque.  A diesel electric hybrid variant of the M113 APC with rubber band tracks was powered exclusively by electric motors and demonstrated incomparably faster acceleration than the standard 6V53T Detroit Diesel powered model.  The US Army's new AMPV APC / IFV from BAE is a diesel electric hybrid and so are the newer Oshkosh HEMTT off-road / tactical trucks.  DARPA now has a Hummer with wheels that turn into tracks for off-road use.

Why Tracks?  Watch what happens in soft terrain:
Tires vs. Mattracks

DARPA Reconfigurable-Wheel-Track (RWT)  The best of both worlds:
Humvee with reconfigurable wheel-track DARPA GXV-T

Hybrid Electric M113:
High-Technology M113 Gavins: Real Future Combat System

Hybrid Electric AMPV:
The Future is Here Today with Hybrid Electric Drive

A small always-on RTG would provide adequate life support because the newer life support equipment is so efficient and the actual power requirements for modern electronics are so low.  A .3kWe RTG and a small bank of super capacitors would be entirely sufficient to handle vehicle life support and electronics.  The solar panel system could provide power to the electric motors.  Substitute the mass of the battery with super capacitors and solar panels.  A 25kWe thin film array might weigh 40kg to 50kg.  Use that power to charge a small bank of super capacitors for daylight travel.  If a major dust storm knocks the array power back to 1% of its rated output, that's still 250We.

Wheels are more efficient than tracks over hard ground because wheels have less friction / traction, which is the very thing that makes a tracked vehicle desirable for off-road operations.  Typical 4 to 8 wheeled military vehicles have far less traction than tracked vehicles of equivalent size.  At low speeds and low to moderate vehicle weights, Aluminum ceramic metal matrix composites with metallic rubber or straight metallic rubber should provide enough strength and wear resistance for the tracks.  The track maintenance that Oldfart1939 mentioned is all but eliminated using rubber band tracks and Thoraeus metallic rubber was developed specifically for use with cryogens, so it should work on Mars in most latitudes.  Daylight only travel will ensure the rubber remains warm enough for use.

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#139 2018-09-14 15:12:49

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,939

Re: Mars Cart

Yes, I think on balance I'm a track man...as with everything on Mars I guess it's a question of getting the right robust materials that don't crack in the extreme weather conditions. One advantage of tracks is that we might well be able to start 3D printing or manufacture of the track links and road wheels at an early stage.


kbd512 wrote:

Louis,

Some of us favor using an all-electric system to negate the issues with storing volatiles aboard pressurized vehicles and the mechanical reliability of virtually any electric motor when compared to virtually any piston or gas turbine combustion engine.  With proper power regulation, it's not even a contest.  The electric motor wins every time.  The power-to-weight ratio and efficiency of modern and inexpensive axial flux permanent magnet electric motors greatly exceeds the largest and most efficient gas turbines in existence.  When money is no object and there's no air resistance to speak of, you can hoist a large thin film sail from the top of your tracked armored personnel carrier and soak up as many trons as you need to provide adequate power.  Electric motors provide gobs of torque.  A diesel electric hybrid variant of the M113 APC with rubber band tracks was powered exclusively by electric motors and demonstrated incomparably faster acceleration than the standard 6V53T Detroit Diesel powered model.  The US Army's new AMPV APC / IFV from BAE is a diesel electric hybrid and so are the newer Oshkosh HEMTT off-road / tactical trucks.  DARPA now has a Hummer with wheels that turn into tracks for off-road use.

Why Tracks?  Watch what happens in soft terrain:
Tires vs. Mattracks

DARPA Reconfigurable-Wheel-Track (RWT)  The best of both worlds:
Humvee with reconfigurable wheel-track DARPA GXV-T

Hybrid Electric M113:
High-Technology M113 Gavins: Real Future Combat System

Hybrid Electric AMPV:
The Future is Here Today with Hybrid Electric Drive

A small always-on RTG would provide adequate life support because the newer life support equipment is so efficient and the actual power requirements for modern electronics are so low.  A .3kWe RTG and a small bank of super capacitors would be entirely sufficient to handle vehicle life support and electronics.  The solar panel system could provide power to the electric motors.  Substitute the mass of the battery with super capacitors and solar panels.  A 25kWe thin film array might weigh 40kg to 50kg.  Use that power to charge a small bank of super capacitors for daylight travel.  If a major dust storm knocks the array power back to 1% of its rated output, that's still 250We.

Wheels are more efficient than tracks over hard ground because wheels have less friction / traction, which is the very thing that makes a tracked vehicle desirable for off-road operations.  Typical 4 to 8 wheeled military vehicles have far less traction than tracked vehicles of equivalent size.  At low speeds and low to moderate vehicle weights, Aluminum ceramic metal matrix composites with metallic rubber or straight metallic rubber should provide enough strength and wear resistance for the tracks.  The track maintenance that Oldfart1939 mentioned is all but eliminated using rubber band tracks and Thoraeus metallic rubber was developed specifically for use with cryogens, so it should work on Mars in most latitudes.  Daylight only travel will ensure the rubber remains warm enough for use.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#140 2018-09-14 18:29:15

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 13,056

Re: Mars Cart

Since this is a vehicle for exploring and not really do the sample testing with in it. We will outfit it with a sample cache box. Possibly with robotic arms to pick the samples up to place them into it rather than alway having to dawn a suit to go get them.

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#141 2018-09-15 00:05:27

kbd512
Member
Registered: 2015-01-02
Posts: 2,113

Re: Mars Cart

SpaceNut,

A remote manipulator arm would be nice, provided that the electro-optics and scientific instruments package for the vehicle is adequate to identify interesting materials found along the way.

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#142 2018-09-15 08:23:18

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 13,056

Re: Mars Cart

Sure a surface for the sample to be cradled on with an array of tools to inspect the sample further such as those of the rovers would be a good start before keeping or returning it to the surface. I would think that we would also start doing a location of sample identification flag system as well. These could be as simple as a flag pin to RFID or beacon in nature of the type so as to mark where a sample is from and to be able to map places of interest.

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#143 2018-09-16 10:55:22

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,231
Website

Re: Mars Cart

The vehicle you design depends upon it intended use.  Is it for exploring?  Is it for hauling equipment and supplies?  Is it for construction of roads and facilities?  Is it for ice mining? Those all have vastly-different requirements,  and are thus vastly different designs. Just like here. 

GW


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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#144 2018-09-16 20:22:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 13,056

Re: Mars Cart

The topic has evolved from a tow behind cart to talking about something more through out it. I did try and narrow up the other topics which were for a light mass open rover for crew to drive. A Nuclear powered rover/ RV sized combined habitat exploration vehicle and other such things.
Early on the first flight if we are still mass restricted we will be looking to using something simular to a lunar rover. As time goes on I am hoping that we will not be restricted and or be able tobuild from what we have on mars something more capable.

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#145 2018-09-18 18:39:15

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 13,056

Re: Mars Cart

More designing reference materials for making a rover for mars and being able to understrand how we will fix it when it breaks.
Electric Motors - Power and Torque vs. Speed

With know battery we will need to control the motor and its speed of movement with a Speed Control of Motors — An Introduction to Variable-Frequency Drives

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#146 2018-09-19 05:06:22

elderflower
Member
Registered: 2016-06-19
Posts: 929

Re: Mars Cart

I think Musk has shot a lot of peoples' foxes with his BFR proposals. Some of the things we were discussing included consideration of how to get by with minimal mass and very few people. These aspects become much less prominent if the BFR comes with the promised capabilities.

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#147 2018-09-19 05:46:29

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,939

Re: Mars Cart

Yes, I agree entirely.  Previously, the game here was to see how missions could be done on the cheap using little mass and as you say a few people. Taking 600 tonnes to Mars for the first mission is a game changer. It's the equivalent of moving 15 houses to Mars or 500 small cars. Also, thanks to the "Magic of Musk" and the multi-purpose capabilities/reusability of the BFR,  it's not actually going to be hugely expensive, as things go.

I think the key questions now are:

1.  What is the most effective route to creating a viable autonomous industrial and agricultural infrastructure on Mars?

2.  What should be the balance between ISRU and importation?

3.  Should you follow a strategy of maximising the human population?

4.  What should be the focus of activity on Mars: exploration? science? industry? commerce with Earth? agriculture? How do you balance these different activities and how do you allocate resources to them?

In terms of designing vehicles for Mars I think it means instead of having one or two multi-purpose vehicles for Mars, we can have a range of vehicles designed for specific purposes:

a. Pressurised electric "Golf cart" type vehicles for people to pass from one pressurised environment to another at the base.

b. Large and robust dual-fuel explorer rovers (for undertaking expeditions to interesting locations).

c. Robot mining vehicles.

d. Road trail vehicles (boulder clearance, to make smooth tracks).

e. Robot transporters - to bring ice, iron ore, sand, basalt and other raw materials to the base.

f.  Construction robot vehicles (diggers, transporters, mobile cranes and so on).






elderflower wrote:

I think Musk has shot a lot of peoples' foxes with his BFR proposals. Some of the things we were discussing included consideration of how to get by with minimal mass and very few people. These aspects become much less prominent if the BFR comes with the promised capabilities.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#148 2018-09-19 15:20:39

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 2,890
Website

Re: Mars Cart

Pressurised electric "Golf cart" type vehicles for people to pass from one pressurised environment to another at the base.

Pah. Just use tunnels. Why are you building them so far apart, anyway?


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#149 2018-09-19 17:57:28

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,939

Re: Mars Cart

Fire or explosion could be a deadly threat to connected buildings.  You probably want to have a couple of hab areas after mission one. You'd need more than one farm hab, to ensure food supply. Your industrial centre and propellant production should definitely be sited a good 500 metres away. The Spaceport clearly would have to be sited far away from the habs. You also will have either an extensive PV system or a nuclear reactor.

Building tunnels between all these elements could amount to building several kms of tunnels - a major building project - and totally unnecessary if people just pop into a pressurised vehicle in an air lock and then drive into the air lock of another location.

Terraformer wrote:

Pressurised electric "Golf cart" type vehicles for people to pass from one pressurised environment to another at the base.

Pah. Just use tunnels. Why are you building them so far apart, anyway?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#150 2018-11-13 12:29:37

DaveRodda
Member
Registered: 2018-11-13
Posts: 1

Re: Mars Cart

Hi...as per my knowledge Scaling up MOXIE to produce propellants for the ERV would require a substantial amount of power, ~12kWe according to MIT and NASA, to produce 2kg of oxygen per hour.  You'd still have to import hydrogen from Earth to make methane.

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