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#51 2004-08-22 01:43:38

MarsDog
Member
From: vancouver canada
Registered: 2004-03-24
Posts: 852

Re: Simple Mars Vehicle Part 1

I could not get more information on the Larson estimate.
However, another comparision, to an Earth based Kwh figure:

Taking a comparable vehicle,  (gentle day to day driving),
which could be increased in weight proportinal to Earth/Mars gravity:

Ford Transit Van (diesel)    2.5 miles per Kwh

6616 Kwh/(m^3 of Methane)  *  2.5 Miles/Kwh= 16540 miles.

Multiply by 0.6 for fuel cell efficiency = 9924 miles
Or by 0.4  for diesel electric             = 6616 miles

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#52 2004-08-22 11:17:22

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Methane can be oxidized directly using a solid oxide fuel cell, however, high concentrations of CH4 lead to severe coking problems.  Therefore, only fuels containing dilute concentrations of CH4 can be oxidized directly in current Solid Oxide Fuel Cell.   

Cells.http://www.nfcrc.uci.edu/fcresources/FCexplained/Fuels.htm

Fuel cells that use a fuel other than hydrogen need a reformer that extracts the hydrogen.  Using a fuel other than hydrogen gets you less hydrogen but there are benefits because hydrogen is difficult to store as a gas or liquid.

Here's an example:
A single alkaline fuel cell (which has 10% better efficiency than the solid oxide fuel cell you would have to use) uses 115.2 cubic feet of hydrogen an hour to produce 12kw (16 horsepower).  Your 1 cubic meter container will hold 61,023 cu in of hydrogen so that comes out to 530.6 hours of use.  If you had a motorcycle you could probably go 20 mph on 16 horsepower so that works out to 10,612 miles.  So, you are about correct. 

But what does that have to do with mars? 

Are you saying a heavy Ford Van that has only 16 horsepower can carry 1 cubic meter of methane (I'm not even including all the life support, oxygen for the fuel cell, food, equipment...) and go over 9,000 miles on mars?[/color:post_uid0]

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#54 2004-09-02 13:31:47

mboeller
Member
From: germany
Registered: 2004-05-08
Posts: 53

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Hi Dook;

have you seen this:

MARVIN: A Proposal for a Long-range Pressurized Rover  473KB PDF

IMHO this Rover resemble's your proposal but without solar cells.


[edit]:

I just forget the next PDF from the second HEDS-UP Forum :

http://www.lpi.usra.edu/publications/re … /texas.pdf [ 584KB PDF ]

They showed an inflatable rover concept with an really ingenious airlock  äähh suitport. The spacesuit is stored outside of the Rover and only the accessport into the spacesuit is sort of an airlock here.[/color:post_uid0]

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#55 2004-09-07 10:26:56

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Just a wild guess
-
To refine the guess, would have to individually calculate effects, such as bearing friction, wind drag, tire rolling resistance on various terrain, electric controller efficiencies, etc.
-
The energy ends up as heat, one way or another. In addition to regenerative braking, regenerative shock absorbing might also increase the range.
-
Quote from one estimate:
"How much power? Hmm... Some back of the envelope calculations: Say the shock absorber on each corner of a 900Kg car needs to slow 225 kg from 1 m/s to 0 m/s in 0.5 seconds. 225 Kg moving 1m/s has 1/2mv^2 = 112.5 KJ of energy. That energy, dissipated in half a second is 225 KW of power. Actually, since the motor isn't 100% effiecient, a bunch of that power never makes it out to the controller. If it was 66% efficient, the controller would only have to handle 150 KW. Of course if the speed was actually 0.5 m/s rather than 1 m/s it would only produce 1/4 the power, so this number is really quite unknown, but I'll go with 150KW for now."
-
Another estimate: Quote from the pdf file
This, in turn,translates into a range of likely regenerated powers: 1.92kW < Power < 17.24 kW and an associated likely range for percentage of recovered power (or energy): namely, 20% < energy recovered < 70%.[/color:post_uid0][/quote:post_uid0]
[color=#000000:post_uid0]Regenerative shock absorbing sounds interesting and may be of some use as long as it does not add too much weight.  I think 200 pounds would be about as much as it could weigh.  The design is still over the weight limit by about 500 pounds.[/color:post_uid0]

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#56 2004-09-07 11:07:23

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

Hi Dook;

have you seen this:

MARVIN: A Proposal for a Long-range Pressurized Rover  473KB PDF

IMHO this Rover resemble's your proposal but without solar cells.


[edit]:

I just forget the next PDF from the second HEDS-UP Forum :

http://www.lpi.usra.edu/publications/re … /texas.pdf [ 584KB PDF ]

They showed an inflatable rover concept with an really ingenious airlock  äähh suitport. The spacesuit is stored outside of the Rover and only the accessport into the spacesuit is sort of an airlock here.

I've seen this proposal before.  I like the combination carbon composite/kevlar honeycomb structure but at 8,819 pounds it's way over the weight limit for mars direct.

Also they don't like the alkaline fuel cell because it will not tolerate CO2 but the fuel cells would be mounted internally and sealed.  Plus you can put baking soda absorbant filters into the fuel cell to absorb any stray CO2.

They need 62.5 kw to run their vehicle.  I hope this is incorrect because it is way more than mine although I did not work out the power requirements to the drivetrain because it was beyond my mathmatical ability.  My vehicle runs entirely on battery and solar panel power to turn the three electric motors.  Each motor provides 8 horsepower.

Also they are discharging the water overboard so this vehicle has a limited range whereas mine has a range only dependant upon the crews food supply.

Their design has the electric motors in the wheel along with a complicated planetary gearbox.  This also needs a slip ring to transfer electricity to the rotating wheel.  I see a lot of problems with this: Mars soil, vibration and shock, exposure to the extreme cold.

Cockpit based upon the Boeing 777?  Completely unnecessary and a waste of money. 

I really don't think a fire suppression system is needed.  Circuit breakers would provide electrical overload protection and any system could be shut down immediately.  Smoke would be a problem though that I had not thought about.  If I add a Hepa filter to the CO2 removal air circulation fan it would be able to remove any smoke in the cabin.  The crew would have to go to the emergency air canisters for a while or maybe go and sit in the rear airlock.

They are completely dependant on lithium hydroxide canisters for CO2 removal which I don't believe would be possible.  I think the canisters weigh about 5 pounds each plus they would use about 2 a day.  They would need to carry about 100.

I really don't believe 3 crew members is necessary.  2 should be enough.

Their round airlock seems okay, but an 8' airlock?  This thing is huge.

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#57 2004-09-07 11:09:46

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,155

Re: Simple Mars Vehicle Part 1

Lithium-Ion batteries when current is drawn nearer to the battery ratings give off quite a bit of heat. so make an insulative blanket to be placed around the pack when in use in the rovers other wise remove and place inside the Mars habitat for climate control while recharging.

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#58 2004-09-07 13:02:16

Dook
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Re: Simple Mars Vehicle Part 1

This vehicle design has an outside electrical connection port that the mars habitat can connect to if necessary so you don't have to move 700 hundred pounds of batteries.  Electricity can flow either way.

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#59 2004-09-09 06:25:35

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,155

Re: Simple Mars Vehicle Part 1

One of the proported failures of possibility for why the pyros on the Genesis probe did not go off is the batteries.

a link sort of discounting the effects of heat on that style of batteries (lithium-dioxide) . But if this truely is the cause maybe a battery pack of mixed types might be in order for the Rover design.

http://www.jpl.nasa.gov/releases/2001/r … 1_214.html

The temperature of the lithium-dioxide battery is currently at 23 degrees Celsius (73 degrees Fahrenheit), within the range anticipated by spacecraft designers. A radiator device intended to shield the battery is not working as well as expected, however, and the battery is likely to heat up to 42 degrees Celsius (108 degrees Fahrenheit). Mission managers consider this temperature to be within acceptable limits. They note that similar batteries have been maintained at 60 degrees Celsius (140 degrees Fahrenheit) for 15 months without impairing their performance. Ground tests are being conducted on lithium batteries to measure their durability at various temperatures.

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#60 2004-12-03 07:49:21

Dook
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From: USA
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Posts: 1,409

Re: Simple Mars Vehicle Part 1

Bump.

Using the figures from The Case for Mars the pressurized rover has a weight allowance of 1.4 tonnes.  If the two open rovers were not sent and their weight allowance used for the pressurized rover then this vehicle can go up to 2.2 tonnes.  If you also apply the .5 tonne weight allowance for the field science equipment then it can be 2.7 tonnes or 5,400 pounds.  Currently my design is estimated to be 4,979 lbs so I am well within the weight allowance.

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#61 2005-01-04 11:42:29

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
Website

Re: Simple Mars Vehicle Part 1

This might be a very useful invention for Mars vehicles:

Reinventing the Wheel (and the Tire, Too)
By NORMAN MAYERSOHN

New York Times, Published: January 3, 2005

GREENVILLE, S.C.

THE first automobile to use air-filled tires was a racecar built by André and Édouard Michelin in the early 1890's. More than a century later, the French company founded by the Michelin brothers is so identified with pneumatic tires that its mascot, Bibendum, is a man made of little else.

Now, after decades spent persuading the world to ride on air, the company has begun work on an innovation that could render the pneumatic tire obsolete. Engineers at Michelin's American technology center here envision a future in which vehicles would ride on what they call the Tweel, a combined tire and wheel that could never go flat because it contains no air.

Arriving at a conference room recently to explain the development project, a research engineer, Bart Thompson, used the Segway Human Transporter that he rode to the meeting to illustrate his points. Aboard this high-tech visual aid - one of those self-balancing electric scooters best remembered for the optimistic claim that it would reinvent personal transportation - Mr. Thompson whizzed down the hallway and out to the lobby, pirouetting among the benches and planters to demonstrate the flexibility of the Tweel.

To be sure, the Segway would be a very small market for Michelin, the world's leading tiremaker, but it is an apt demonstration vehicle for the Tweel. The first commercial use of the integrated tire and wheel assembly will be on the stair-climbing iBOT wheelchair, another product developed by Dean Kamen, the Segway's inventor; Michelin said it would announce another application at the Detroit auto show next week.

The tiremaker has high expectations for the Tweel project. The concept of a single-piece tire and wheel assembly is one the company expects to spread to passenger cars and, eventually, to construction equipment and aircraft.

The Tweel offers a number of benefits beyond the obvious attraction of being impervious to nails in the road. The tread will last two to three times as long as today's radial tires, Michelin says, and when it does wear thin it can be retreaded.

For manufacturers, the Tweel offers an opportunity to reduce the number of parts, eliminating most of the 23 components of a typical new tire as well as the costly air-pressure monitors that will soon be required on new vehicles in the United States.

In recent years, manufacturers have devoted an increasing amount of attention to tires that let motorists continue driving after a puncture, for 100 miles or more, at a reduced speed. Several such "run flat" designs are now available, providing convenience and peace of mind for travelers as well as freeing automakers to eliminate the weight and cost of spare tires.

Michelin, which markets run-flat tires under the Pax name, took a different approach in developing the Tweel. Its goal: a replacement for traditional tires that is designed to function without air in the first place.

Mounted on a car, the Tweel is a single unit, though it actually begins as an assembly of four pieces bonded together: the hub, a polyurethane spoke section, a "shear band" surrounding the spokes, and the tread band - the rubber layer that wraps around the circumference and touches the pavement.

While the Tweel's hub functions as it would in a normal wheel - a rigid attachment point to the axle - the polyurethane spokes are flexible to help absorb road impacts. The shear band surrounding the spokes effectively takes the place of the air pressure, distributing the load. The tread is similar in appearance to a conventional tire.

One of the basic shortcomings of a tire filled with air is that the inflation pressure is distributed equally around the tire, both up and down (vertically) as well as side-to side (laterally). That property keeps the tire round, but it also means that raising the pressure to improve cornering - increasing lateral stiffness - also adds up-down stiffness, making the ride harsher.

With the Tweel's injection-molded spokes, those characteristics are no longer linked - a point of particular excitement to an engineer like Mr. Thompson because of the potential it holds for improving handling response. The spokes can be engineered to give the Tweel five times as much lateral stiffness as current pneumatic tires without any loss of ride comfort.

The Tweel auto project is in its infancy - "Version 1.0," Mr. Thompson said - and only a single set of car Tweels exist. A test drive in a Tweel-equipped Audi A4 sedan on roads around Michelin's research center proved to be far less exotic than the construction method or appearance would suggest. The prototype Tweels are noisy, as Mr. Thompson warned they would be, a problem traced to vibration in the spokes.

The Tweels also transmit more of the feel of a coarse road surface than customers would tolerate in a production tire, but the level is understandable considering the early stage of development. More important, the steering's response as the driver begins a turn is excellent, and large bumps were swallowed up easily by the Tweels and the Audi's unmodified suspension.

There are other negatives: the flexibility, at this stage, contributes to greater friction, though it is within 5 percent of that generated by a conventional radial tire. And so far, the Tweel is no lighter than the tire and wheel it replaces.

Almost everything else about the Tweel is undetermined at this early stage of development, including serious matters like cost and frivolous questions like the possibilities of chrome-plating.

Logical uses - military vehicles, for example - would come years before automobiles, but Michelin's business projections accommodate the possibility that the Tweel may not be an overnight success. This would be nothing new for Michelin: the radial tire it invented in 1946 was not widely accepted in the United States until the 1970's

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#62 2005-08-09 04:45:19

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

With the recent discoveries of what appears to be surface ice in craters and places other than the extreme poles I think this vehicle design is even more useful. 

The planned route that an exploration crew would take across mars could pass by known ice deposits where the crew could chip away or drill ice chunks and place them in the stainless steel water reservoir that supplies the Teledyne electrolysis machines that convert the water to hydrogen and oxygen for the fuel cells. 

It's range is essentially only limited by the crew's food supply and carried air supply.  The vehicle could make a series of excursions, returning to the habitat with core samples and to resupply with MRE's and air then venturing off again in other directions.

Only problem I see is if there is dry ice with the ice.  Then the CO2 would evaporate and contaminate the atmosphere inside the vehicle, perhaps to a toxic level.

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#63 2005-08-10 16:57:48

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

Huh? You want to use solar cells to crack water to run fuel cells to power your rover?

Water isn't fuel! Fuel cells are only an energy storage medium, not an energy source: it takes alot of power, infact more power then the fuel cell can generate, to split the water into hydrogen and oxygen. This is simple thermodynamics stuff.

The problem with solar pannels, even the nice crystalline gallium-arsenide kind, is that they don't generate enough power on their own to operate and warm (during night) the rover on their own.

You have got to augment your supply of power with something, such as bringing along extra hydrogen/oxygen or a bank of those new dynamic RTGs (with much greater power-per-pound).

You don't need to worry about supplying water to an electrolysis machine, because you can just condense and reuse the water from the fuel cell, which will make ~100% of the hydrogen and oxygen needed to operate the fuel cell. More then that if you operate the cell open-cycle to eliminate the need for extra power generation.

Water is not fuel, and fuel cells are not an energy source! It takes gobs of energy to split water into Hydrogen and Oxygen.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#64 2005-08-11 04:35:38

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

According to NASA the space shuttles alkaline fuel cell produces 12kw of power (16kw max) and uses 48.3 cu ft of oxygen and 112 cu ft of hydrogen per hour.  Titan's website says it's Teledyne HM system uses 6kw an hour and produces 52 cu ft of oxygen and about 106 cu ft of hydrogen.  A fuel cell would be operated along with one electrolysis system.  I know something sounds fishy because we have a power surplus of 6kw and never lose any water/oxygen/hydrogen.  The only waste is heat to the vehicle.  Something can't be right with the Titan electricity use numbers.

The extra hydrogen/oxygen that you suggest bringing along is contained in the external bottles.  The bottles hold 435 cu ft and there are five hydrogen and two oxygen.  There should be enough for 18 hours of continuous use but that only accounts for one use of the stored hyd/oxy.  Mars ice melted and used by the Titan systems (if they really are that efficient) would provide more fuel cell use. 

The solar panels are simply a supplement and necessary emergency backup for battery recharging.  The solar panels will likely only produce 3kw max at high noon and somewhere around 6kw total per clear day.  Along with the foldable emergency solar panel they would provide enough power to move the vehicle a limited amount each day while keeping onboard systems operational.   

I doubt internal heating would even be necessary.  If a single mylar layered dome would get too hot during the martian day then this vehicle with carbon composite and polyethylene insulation would definately hold heat in well.  In fact it probably needs some kind of cabin cooling device.

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#65 2005-08-11 07:21:38

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

"I know something sounds fishy because we have a power surplus of 6kw and never lose any water/oxygen/hydrogen"

Now theres' an understatement, because such an arrangement is against the laws of physics. One or more of three things must be true:

-Shuttle's APUs can't generate that much power, which I think is unlikly, why would NASA lie? What you may be confused with is that Shuttle carries three fuel cells, are you sure that the power output isn't for all three APUs, but the gas requirement is for only a single one?

-The Teledyne's power consumption or water conversion claims are wrong, and in a BIG way, or else there is something in the "fine print", such as a high operating temperature.

-"Cubic feet" of gas produced or consumed is at different pressure between what the Teledyne produces or the APUs consume, so comparing the two figures directly is the source of the error.

Edit: If each Shuttle generator produced 4kW each, then that would make sense.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#66 2005-08-16 15:15:28

Rxke
Member
From: Belgium
Registered: 2003-11-03
Posts: 3,658

Re: Simple Mars Vehicle Part 1

About that tweel...

http://hoop.exblog.jp/1693089

left one would be a nifty rock-climber... esp. if it were powered. Imagine a guy in a suit on it...

(Edit)

Scroll dow for the CAT picture, too.  8)


ExoMars' launcher's 2nd stage is probably en route to Mars. Unsterilised... yikes

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#67 2005-08-17 05:58:09

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,155

Re: Simple Mars Vehicle Part 1

The top photo is a product that is made by deka research owner Dean Kamen here in NH. He is the maker of the segway, and the iBOT Mobility System as well.

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#68 2005-09-09 12:53:04

mboeller
Member
From: germany
Registered: 2004-05-08
Posts: 53

Re: Simple Mars Vehicle Part 1

Hi Dook;

maybe this is something for your vehicle:

http://www.amminex.com/index_files/Page344.htm


AMMINEX uses a new concept for hydrogen storage. Hydrogen is delivered from an integrated system containing the AMMINEX storage material.

The proprietary solid storage material holds more than 9 weight-% hydrogen.

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#69 2005-09-09 13:55:40

publiusr
Member
From: Alabama
Registered: 2005-02-24
Posts: 682

Re: Simple Mars Vehicle Part 1

Page 72 and page 33 of the Oct. 2005 iss. of Pop Mech has some nice car tech.

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#70 2005-09-11 21:30:39

Dook
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From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

Something I picked up somewhere about metal hydride tanks:

The total amount of hydrogen absorbed is generally 1% - 2% of the total weight of the tank. Some metal hydrides are capable of storing 5% - 7% of their own weight, but only when heated to temperatures of 2500 C or higher. The percentage of gas absorbed to volume of the metal is still relatively low, but hydrides offer a valuable solution to hydrogen storage.

So this Amminex seems to hold more hydrogen by weight.

But I think the storage bottles I've chosen hold more(435 cu ft).  Also I think the vehicle would have to use liquid oxygen and hydrogen.  It's storage bottles can be shipped full of hydrogen and oxygen gas then filled with liquid hydrogen and oxygen on mars from the in-situ.  This is included in Zubrin's Mars Direct plan.

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#71 2005-10-13 08:56:04

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
Website

Re: Simple Mars Vehicle Part 1

This link summarizes the DARPA race of robotic vehicles:

http://www.spacewar.com/news/robot-05zzzc.html

Self-driving vehicles could be a huge benefit:

1. An expedition could set out with two manned vehicles and robotic cargo vehicles following behind

2. Once you have two bases and a dirt track in between, robotic trucks could carry stuff back and forth.

                    -- RobS

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#72 2005-12-04 06:53:31

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

One problem with exploring the surface of mars is that once you cross the horizon you lose contact with your base and cannot depend on a compass or GPS to determine your location.  You will have nothing to guide you across mars and back to your home base.

The Mars Reconnaissance Orbiter will soon take high resolution pictures of the martian surface revealing images as small as one yard.  I think we should be able to use these pictures, and Spirit and Opportunity's pictures as well, to come up with a 3D map of mars as viewed from the surface. 

Two explorers in a pressurized exploration vehicle driving across mars could each have laptops with computer programs that show a 3D computerized view of their projected course.  They would be able to turn the view, look left and right, and they could just click on the screen and the program would advance to a location ahead, maybe 10 miles with each click.

There would also have to be an overhead view that tracks their course so they could plan their way to known mars locations.

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#73 2006-02-07 15:56:49

Designer
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Registered: 2006-02-07
Posts: 8

Re: Simple Mars Vehicle Part 1

Thank You, Really cool explanation! I learnd alot!
Please cheack my topic at >>Human missions>Crew Exploration vehicle 2030 "manned rover.
I really appreciate your ideas and opinions.

Regards, Hirash

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#74 2006-03-13 19:06:45

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

Some modifications to the original design.

The Titan Systems have been removed because there is no way they can efficiently convert water back into oxygen and hydrogen.  It's a net loss of energy, not a gain. 

So to make up for it there must be more hydrogen and oxygen bottles.  So I've increased to fourteen bottles (ten hydrogen/four oxygen).  This adds a lot of weight so the second lithium-ion battery pack has been removed also. 

The vehicle would need to be operated in a specific manner to get the most range which I estimate to be 702 miles, 351 miles one way.  The crew would recharge the vehicles batteries for one full day, the next morning one fuel cell would be powered up for one hour and the vehicle driven as far as it can go (about 27 miles).  Then stop and conduct area surveys the rest of that day and the next.  Using the vehicle every other day would allow the solar panels to charge the batteries. 

Also I wish to keep the carbon composite construction.  There are concerns that the vehicle would get too hot inside with a fuel cell and the electric motors running because of the superior insulation that carbon composite provides over aluminum but the fuel cell and motors would only be operated for about an hour or slightly more per day.  Also there is concern that UV rays would damage the carbon composites.  I haven't come across any evidence of this, carbon composites are on mars rovers now. 

The total vehicle weight is now 5,687 lbs, too much to meet Mars Direct requirements. 

If somehow this MEV can weigh another 700 lbs then a second lithium-ion battery pack should be installed.  This would double the vehicles range if operated in the most efficient manner as stated above.

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#75 2006-03-13 20:58:36

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,155

Re: Simple Mars Vehicle Part 1

You may want to make sure that you are able to have the 2 sets of Lithium -ion batteries. If current draw is heavy and continues for sufficient periods of time the internal temperature of the batteries will cause them to break down. Also if the voltage value drops to low per cell between recharging it could lead to reverse polarity reversal as well.

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