Running on Compressed Air?

quasar777 · 2004-10-06 04:07:31

we need an OuterSpace Patent Office.

SpaceNut · 2004-10-06 07:32:16

In addition to the use of CA for tool use (just look at any auto repair shop for how useful) and for vehicles to travel the surface, one could also transfer the container tanks to a refining and seperations plant. Cooling to form liquids of each gas that the atmosphere contains for future use.

C M Edwards · 2004-10-06 13:53:52

we need an OuterSpace Patent Office.

Heavens, yes! But that's a whole other thread.

TwinBeam · 2004-11-22 12:53:16

A few factors that appear to have been overlooked:

Aircar with 450 liter tankage offers 416miles range at 12mph vs 71 miles at 30mph - i.e. air resistance increases as square of velocity. Mars is near vacuum - so 400miles range is a better guess. Liquid CO2 can genenerate about 4x the gas pressure - so 1600mile range sees reasonable - 5 days of driving at 30mph, 10hr/day. Extend that indefinitely by stopping and using solar power to generate more liquid CO2 while you explore an area.

Need a heat source, and Mars atmosphere is poor, especially at night, assuming you're using the CO2 engine to power a generator. Maybe carry tanks of molten salts? Heat exchangers might be adequate during the day. Or a low-power, solid-state nuclear heat source. A pure alpha particle emitter, so shielding is trivial.

sethmckiness · 2004-11-23 05:48:49

WOW!

I really like this idea.

The strengths of the CA idea would lend for a short trip slower moving rover of small size. I think the real debate should be how this energy is harnessed to drive wheels etc. But something where the vehicle was built around the tank for protection of the tank, and hauling 2 people and perhaps 100 kg or so of scientific equipment and or samples would make this a good little get around vehicle.

Coupled with efficient design, minimal rolling resistance and Gross Vehicle Weight, this would work amazingly well.

My only thought would be if you wanted to enhance the capability would be add some sort of reactant to the compressed air to increase the energy. But, I think just compressed air for power to the wheels and a 12 Volt battery of some sort to power on board electronics should suffive for a very simplistic and very usable design that would also be very BUDGET FRIENDLY!

Rxke · 2004-11-23 06:53:19

good point re the power tools on compressed air. This could be some kind of a swiss-knife little car, buzzing around the base, plug in your power tools do do jobs etc... Nowadays when the people that break up the street etc come around, they lug a generator for compressed air, but that wouldn't be necc. in this case.

GCNRevenger · 2004-11-23 09:22:42

The big issue with a vehicle like this is how heavy it will be. The CA car here on Earth relies on its light weight to achieve its range, but on Mars you would need several fairly heavy things that you wouldn't on Earth... for instance, the pressure vessel & thick windows, the LSS system (CO2 scrub, H20 recycling/tankage, thermal), batteries and/or a dynamic RTG, CO2 compressor, heavier tank to handle the mass of liquid CO2, bigger wheels & suspension, heavier duty tranmission, and enough bottled breathing gas for multiple cabin or airlock cycles.

It will be neither light weight or cheap.

Rxke · 2004-11-23 09:53:33

Oh... I was thinking about an oversized moonbuggy, seating maximum four in pressure suits, main task to rove crew around near vincinity of the base... Like jaunts to the reactor or landing/launch spot etc...

SpaceNut · 2004-11-23 10:02:13

I agree do not go for the all enclosed unit, for most of its use they are in an out to often to do the scientific research and exploration of the surface for an enclosed unit to make sense.

GCNRevenger · 2004-11-23 10:56:07

Somthing unpressurized makes more sense, yes, but it still won't be quite as simple or light weight as the Earthly model, at least not without some pretty exotic materials ($$$).

I wonder if Mars is warm enough to handle the liquid/gas phase transition... solar pannels & batteries may suppliment electrical requirements, but I also wonder if the vehicle won't need a compressed gas turbine generator too.

SpaceNut · 2004-11-23 12:20:25

NASA Concludes First International Workshop in Support of U.S. 'Vision'

Mars lander? This artist's concept shows astronauts using an unpressurized rover to unload cargo and supplies needed for their stay on the Red Planet.

Timeslicer · 2004-11-24 00:31:40

RE: Rover weight - no doubt an enclosed exploration rover will need to be much larger than the aircar - but the CO2 storage could be scaled up as well. And while a Mars vehicle will need more massive construction than the AirCar, gravity is 1/3 Earth, which should help considerably.

While the Aircar stores compressed air at 300barr (~300x atmospheric pressure), there's probably no reason to store the CO2 at super-high pressure - store dry ice in insulated tanks at maybe 10atm pressure, so that as it warms up, it just melts, allowing liquid CO2 to be pumped off to a higher pressure expansion-warming chamber - perhaps directly into the engine itself.

A method to avoid the "rocket effect" of a tank puncture: the tank will be protected by insulation, but in case something does puncture it, surround the tank with an outer perforated metal "diffuser" shell, to spread and slow the expanding gas.

GCNRevenger · 2004-11-24 07:11:35

My problem is that a Martian car will be fundimentally heavier then an Earthly car, while the compressed gas engine will offer no more power-per-pound on Mars then on Earth.

So, heavier car, but no additional power.

The idea of using solid or liquid CO2 has one drawback, that in order to sublimate or boil the condensed CO2, it has to be heated. On Earth, that heat comes from our naturally luke-warm and thick air, but on Mars (especially at night) there is much less thermal energy to be had.

Plus, the engine operates when the pressure on the input side is at its highest, so feeding directly from a low-pressure tank won't get you anywhere, either an intermediate stage or sticking purely with high-pressure gas tankage will be nessesarry.

C M Edwards · 2004-11-24 14:23:23

My problem is that a Martian car will be fundimentally heavier then an Earthly car

You've made a good case for more massive, but heavier?

GCNRevenger · 2004-11-24 14:36:48

Weight, mass, whatever... It will have more mass then a comperable Earth vehicle. Non-chemists aren't usually comfy with the term "masses."

You may have a little bit more energy per pound because of the lower ambient Martian air pressure, but it won't be by much.

Dook · 2004-11-24 15:26:45

In my opinion an unpressurized mars exploration vehicle is not a serious attempt at exploration. The crew would have to wear pressure suits the entire time and I can't imagine a mission being more than 8 hours tops so how far can you go in that amount of time?

As for the weight/mass issue. Yes mars has 1/3 the gravity but the problem is not the vehicles weight on mars but it's launch weight from the earth. Once it gets there who cares?

BWhite · 2004-11-24 15:31:04

The big issue with a vehicle like this is how heavy it will be. The CA car here on Earth relies on its light weight to achieve its range, but on Mars you would need several fairly heavy things that you wouldn't on Earth... for instance, the pressure vessel & thick windows, the LSS system (CO2 scrub, H20 recycling/tankage, thermal), batteries and/or a dynamic RTG, CO2 compressor, heavier tank to handle the mass of liquid CO2, bigger wheels & suspension, heavier duty tranmission, and enough bottled breathing gas for multiple cabin or airlock cycles.
It will be neither light weight or cheap.

You do not need a pressurized compartment at all while working at the base. Find a place for a few suited up astronauts to sit on top while it zooms around the landing site, with outlets for power tools with a hitch to pull a trailer.

= = =

Maybe someone can build one to bring to the Mars Society convention next August.

= = =

Among other uses? Add an attachment to clean dust and fines off the solar panels. Drive the air powered "mule" around the base, using compressed air to clean the solar panels.

John Creighton · 2004-11-24 15:40:16

Why not add some combustion for that extra kick? Perhaps oxygen on compressed tank and methane in another. Maybe the car could be made so it could run with and without combustion.

BWhite · 2004-11-24 15:40:42

In my opinion an unpressurized mars exploration vehicle is not a serious attempt at exploration. The crew would have to wear pressure suits the entire time and I can't imagine a mission being more than 8 hours tops so how far can you go in that amount of time?
As for the weight/mass issue. Yes mars has 1/3 the gravity but the problem is not the vehicles weight on mars but it's launch weight from the earth. Once it gets there who cares?

One vehicle won't solve every problem. For long range travel, I believe you want internal combustion engines. LOX/methane for example.

Why? So you can rev up the engine and power your way out of tough spots like with a Terran 4x4. Start with a Hummer - - swap in a methane/LOX engine and go from there.

Hummer too small in volume? Add an articulated trailer and then enclose the entire volume adding a flexible tunnel from the trailer to the Hummer. Primary airlock is in the trailer.

Timeslicer · 2004-11-24 16:51:55

The hitch-on pressurized trailer is smart - allowing using the tractor for other purposes around base or out exploring. With all the power systems in the "tractor", the trailer can be relatively light - a multi-layer inflatable structure perhaps. That keeps it compact for transport but fast to set up.

A hybrid engine might be a good solution to the heat issue - you're going to need a heat source anyhow, so carry a modest amount of carbon and the O2 to burn it. Use that to heat the CO2 above it's (very low) evaporation point, and the CO2 to run the engine. (Using a hydrocarbon based fuel seems wasteful of hydrogen, which will probably be in somewhat short supply.)

There would need to be small but strong boilers for warming CO2 - but the dry ice can be kept in relatively light tanks - or even just a well insulated cupboard, with the explorers manually moving bricks over to an expansion tank when it runs out of gas.

Heh - I'm getting an image of a future Martian railroad, with the fireman tossing logs of CO2 into the boiler and logs of charcoal into the firebox.

Rxke · 2004-11-25 02:33:02

Dook, it's not for exploration... It's for a semi-big base, with more than one wheeled vehicule.
Imagine some kind of seriously souped up go-cart for the tech-crew, so they don't have to haul everything by hand, a 'donkey,' if you want.
The bigger exporation-rover(s) can then be used for what they're meant to:explore.

The thing would be used for maintnance assistance etc, shouldn't be fast or anything, just a useful jack of all trades.

Dook · 2004-11-25 08:04:29

Sounds like the truck that Zubrin talks about in The Case for Mars. He alots .5 tonnes for it but there are 2 open rovers also, with a total weight of .8 tonnes. So I guess if you just had this vehicle and the pressurized exploration vehicle (don't take the 2 open rovers) then this truck could weigh 1.3 tonnes max.

Rxke · 2004-11-25 09:33:02

Heh...
Crew of 4; 2 open rovers AND an addtional one... Little bit of overkill anyway, no?

Good point, Dook. Scrap one, by all means...

Trebuchet · 2004-11-25 09:52:29

IIRC the 'truck' was for moving heavy stuff like the nuclear reactor around. Probably not neccessary on many Mars missions... on the other hand, a half-ton truck? That's a very, very light vehicle (~1000 pounds), for comparison the Geo Metro - not exactly a Hummer - weighs about 1800 pounds. Maybe it's build out of composites... I remember reading that one of the car manufacturers, Ford if memory serves, built a composite chassis that weighed only 100 pounds.

But it does mean we can't replace the engine in a Silverado and fire it to Mars. Nuts. :laugh:

sethmckiness · 2004-11-25 13:34:07

AS far as vehicle weight, if this was an aorund base and short jaunt vehicle, I see no reason for it to be more then 1 ton. if you want 4wd, use two CA drive motors, one on each end. Use 6AL/4V Titanium, which is light and incredible strong, and less brittle. other then that, all you have is basicly a gator. 4 wheels, a drive system, a brake system. 12v DC Battery (probably the heaviest single component), a simple leaf spring non dampened suspension(it isn't going more then 10 mph). some glorified lawn chairs.. a simple vhf radio. Maybe some emergency oxygen tanks if they run short. Using the KISS method, I wouldn't be suprised if this thing could be brought in at less then 1200 lbs. The key is not trying to make it do everything. IT will be like a golf cart!

WOOOOOOOHOOOOO!

sorry, a 1-2 million dollar golf cart sounds interesting..

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#26 2004-10-06 04:07:31

Re: Running on Compressed Air?

#27 2004-10-06 07:32:16

Re: Running on Compressed Air?

#28 2004-10-06 13:53:52

Re: Running on Compressed Air?

#29 2004-11-22 12:53:16

Re: Running on Compressed Air?

#30 2004-11-23 05:48:49

Re: Running on Compressed Air?

#31 2004-11-23 06:53:19

Re: Running on Compressed Air?

#32 2004-11-23 09:22:42

Re: Running on Compressed Air?

#33 2004-11-23 09:53:33

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#34 2004-11-23 10:02:13

Re: Running on Compressed Air?

#35 2004-11-23 10:56:07

Re: Running on Compressed Air?

#36 2004-11-23 12:20:25

Re: Running on Compressed Air?

#37 2004-11-24 00:31:40

Re: Running on Compressed Air?

#38 2004-11-24 07:11:35

Re: Running on Compressed Air?

#39 2004-11-24 14:23:23

Re: Running on Compressed Air?

#40 2004-11-24 14:36:48

Re: Running on Compressed Air?

#41 2004-11-24 15:26:45

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#42 2004-11-24 15:31:04

Re: Running on Compressed Air?

#43 2004-11-24 15:40:16

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#44 2004-11-24 15:40:42

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#45 2004-11-24 16:51:55

Re: Running on Compressed Air?

#46 2004-11-25 02:33:02

Re: Running on Compressed Air?

#47 2004-11-25 08:04:29

Re: Running on Compressed Air?

#48 2004-11-25 09:33:02

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#49 2004-11-25 09:52:29

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#50 2004-11-25 13:34:07

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