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#1 2004-08-05 16:20:28

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

Re: Simple Mars Vehicle Part 1

Mars Manned Exploration Vehicle  Part 1

This mars manned exploration vehicle idea does not differ much from the wheeled cylinder designs that can be viewed at various web sites but it goes more into detail about the vehicles inner workings.  The design tries to achieve the mission goal while remaining cost efficient since that was the basic idea put forward in the Mars Direct plan.  Simplicity of function is the main focus taking into account cost and weight while providing an acceptable level of redundancy for mission essential and crew life support systems.  I know NASA's reaction to much of this would be absolute shock.  Imagine having an astronaut operate a manual shutoff valve!  Keep it simple and it will work.  Make it unnecessarily complex and it will fail at ten times the cost.  Using the weight figure from The Case for Mars the pressurized rover has a weight allowance of 1.4 tonnes.  If the two open rovers were not sent (keep the open truck) and their weight allowance used for the pressurized rover then this vehicle can go up to 2.2 tonnes.  Currently the design is estimated to be just over that weight limit at 4,650 lbs.

The vehicle is designed to carry a crew of two and operate primarily during the day using the combination of power supplied from it's solar panels and batteries.  At dusk a fuel cell would be turned on for an hour or so to recharge the batteries for the night.  All mission/life essential systems have at least one backup system.   

Each crewmember will have their own portable laptop computer that can act as a mission recorder/diary for each astronaut as well as be a backup vehicle main computer that can connect to the rover's system to monitor oxygen/C02/temperature/pressurization.  Each laptop can also operate the high frequency radio if necessary.   

Vehicle Structure
Carbon composite honeycomb core tube that is 8' wide and 17' long.  Carbon composite construction provides an excellent strength to weight ratio and reduces the amount of heat loss compared to metal construction.  Stainless steel bolts shimmed with PTFE washers attach the forward cone section, aft internal pressure bulkhead, and the aft bulkhead to the cylindrical body.  Four triangular shaped plexiglass windows provide the viewing area for the driver and passenger.  When the vehicle is not in motion insulated covers are affixed by velcro over the inside of the windows to reduce internal heat loss.  The cabin floor is made of fiberglass panels supported by fiberglass ribs.  The floor panels can be opened to gain access to the underfloor storage areas.  The vehicle has two internal aft bulkheads that provide a depressurization area for outside excursions.  The aft depressurization area has a 30" wide pressure door to the outside and storage for two space suits.  A chrome-moly front brush guard surrounds the front of the vehicle to protect it from rocks.  The brush guard is bolted to the vehicles front suspension mounts and has provisions for mounting a front bulldozer scoop that a future mission could bring so the vehicle can be used to clear rocks and move soil.  Two rubber shimmed steel bands surround the composite body, one at the front and one at the rear.  These thin eight inch wide steel bands attach the body to the suspension mounts and have loops at the top for the mars delivery vehicle hoist cables to attach to as well.  The driving station at the front inside cabin is very simple: two captain's chairs, drivers accelerator pedal, brake pedal, steering wheel, one HF radio (2 more in back) and switches that send power to the front gearbox or external lights.  A hose can be brought down from the crew habitation module and hooked up to a fitting on the externally mounted oxygen bottle lines to provide the vehicle with it's initial air supply and pressurize it to 5 pounds per square inch. 
weight @ 900 lbs?

Suspension
Four lightweight five foot tall, 1/4" thick, half-dome shaped aluminum wheels with multiple rounded rubber grips.  The wheels provide 24" of ground clearance.  Each wheel is independently mounted and uses double spring suspension with multiple spring steel shock reducers to limit wheel bounce.  The rounded rubber grips have a soft interior (rubber honeycomb?) to help absorb vibrations.  A thin kevlar rock guard is mounted between each wheel and the vehicle.  An electric steering system is mounted on the forward two wheels and disc/caliper style brakes actuated by a solenoid can slow the vehicle if necessary. 
weight @ 400 lbs?

Electricity Generation
Two internally mounted sealed alkaline fuel cells mix oxygen and hydrogen to provide 12kw of electricity each (16kw each surge) to the propulsion motors and pure hot water as a byproduct.  They send power to the Main AC bus but they can be individually turned on and tied to the Essential AC bus if necessary.  Waste heat (125-500 degrees F) from the fuel cells keeps the interior of the vehicle warm during the day.  The water produced by the fuel cells flows into the stainless steel storage tank mounted beneath.  They are both mounted on the right side, forward, and powered (self warming) by the Essential AC bus, backup bus main AC. 
weight @ 260 lbs ea fuel cell, total weight 520 lbs

Ten, 167cm x 83cm, Gallium Arsenide on Germanium (GaAs/Ge) solar panels, 5.5 mil thick, mounted to a frame on top of the vehicle.  The solar panels provide 1.5 kw (at noon).  This power goes to the AC Essential bus.  The solar panel frame can be tilted @ 40 degrees so the sunlight hits the panels more directly.     
http://mars.jpl.nasa.gov/roverpwr/power.html
weight 17 lbs per panel, estimate 200 lbs total including frame

26 module NiMH batteries mounted just forward of the centerline in a pressurized and insulated area under the cabin floor.  These batteries provide 26 kwh of power to two separate AC (Essential and Main) busses for operating the vehicles systems.  The batteries are easily accessed from inside the vehicle.  There is an external electric recharge connection for initial battery charging from the mars habitat but power can also be used for other equipment on the rover or sent from the rover to the habitat. 
http://www.hondaev.org/batt.html
weight 850 lbs

Propulsion Motors
Three CSIRO 6kw (8hp each) electric motors mounted inside a composite cased reduction gearbox.  This gearbox is located at the center forward of the vehicle between the front wheels.  Carbon composite main rear wheel shafts travel out from the gearbox and go through union joints to the rear wheels.  The reduction gearbox is mounted in an unpressurized area under the vehicle floor.  There is a sealed panel mounted beneath to protect it from mars dust and rocks.  The forward gearbox has a reduction ratio of 11 to 1 and the rear is a 7.52 to 1 ratio gearbox.  As the vehicle movement pedal is depressed 80% of the available electricity in the Main AC bus goes to the front gearbox and 20% goes to the rear gearbox.  As the pedal travels further the ratio changes so that 100% of the power goes to the rear gearbox.  The motors are operated by the Main AC bus but can be tied to the Essential AC bus. The CSIRO motors have an efficiency rate of 98% and produce 3.6kw at 1,060 rev/min with a peak of 6 kw.
http://www.tip.csiro.au/Machines
weight @ 47 lbs just for three motors, gearbox estimate another 50 lbs ea, total of 200 lbs

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#2 2004-08-05 16:22:17

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

Re: Simple Mars Vehicle Part 1

Mars Manned Exploration Vehicle   Part 2

Hydrogen Storage
Eight compressed cylinders with 435 cu ft internal storage are mounted horizontally to the outside of the vehicle, four on each side between the wheels.  The tanks send hydrogen into a common line that leads to the fuel cells.  The tank valves are opened and used one at a time to minimize the risk of losing all of your hydrogen supply from a line leak.  The hydrogen warms as it expands to room temperature providing additional heat to the vehicle.
http://www.cyl-tec.com/cylinderspecs.htm
weight 1,148 lbs total (each bottle weighs 148 lbs)

Hydrogen/Oxygen Converters
Two Teledyne Titan HM-50 Hydrogen/Oxygen electrolysis systems take water from the stainless steel storage tank and separate it into oxygen (99% pure) and hydrogen (99% pure).  The oxygen and hydrogen go through separate lines back to the fuel cells.  These units are mounted on the right side aft of the fuel cells.  Powered by the Essential AC buss but can be manually turned off, back up bus-Main AC.
http://www.teledynees.com/titan.asp
weight @ 150 lbs?

Carbon Dioxide Removal
A centerline mounted small, quiet (26 dba), fan (1.25 watt/55 cfm) operates continuously, night and day, to pull cabin air into a tube that directs the air over the two carbon dioxide continuous scrubbers that remove carbon dioxide down to <10ppm.  The C02 is discharged overboard.  The air leaving the C02 scrubber then passes over heat radiating fins on the stainless steel water tank to provide warm air circulation.  Mounted on the right side, middle, aft of the Hyd/Oxy converters.  Primarily powered by the Essential AC buss, backup powered by the main AC buss.
http://www.coolco2.com/scrubber.html
Problem: how much power does this use? weight?

Miscellaneous Equipment
A four gallon stainless steel water storage tank is mounted beneath the fuel cells to catch the hot water produced by the fuel cells.  A line from the stainless steel tank leads to another, accumulator type design, 12 gallon water storage tank that is mounted vertically next to the shower/toilet.  Water from the stainless steel tank can be pumped by hand into this accumulator which then moves the internal piston upward compressing the atmospheric air trapped in the top portion of the accumulator.  This accumulator can then provide warm pressurized water to the shower.
weight-not much, shipped empty

Two air (oxygen/nitrogen mix) storage bottles are mounted inside the vehicle.  These bottles supply air or oxygen directly to the vehicles pressurization/oxygenation system that maintains 5 lbs internal pressure and keeps the oxygen level at 21%.  There is a manual air valve mounted on the supply line that can be opened in an emergency to pressurize and provide air in the cabin if the automatic system fails.
http://www.cyl-tec.com/cylinderspecs.htm
weight 300 lbs

Either or both of the crew's laptop computers would be hooked into the vehicles monitoring system to monitor battery charging level, solar panel and fuel cell electric production levels, oxygen/C02 levels, inside and outside temperature, and internal pressure.  A warning alarm sounds if anything goes outside of normal parameters.   
weight 100 lbs

Shower/Toilet:  An enclosed fiberglass walled shower is mounted in the center of the cabin.  It serves a dual purpose: a shower and a toilet.  When used as a toilet a hinged carbon composite shower floor panel is placed in the upright position to provide an opening to the upper waste water hold and a hinged toilet seat can be folded down for use.  When used as a shower the toilet seat is folded up against the wall and the shower floor is lowered to stand on.  Holes in the carbon composite shower floor allow the water to flow into the upper waste water hold tank.  A tall, 12 gallon accumulator type water storage tank is mounted next to the shower/toilet to provide pressurized water to the shower head to be used for drinking or showering.  The waste water flows down into the waste water storage tank which has an upper and lower section.  Waste shower/toilet water will fill the upper section then the crew, inside the vehicle, manually opens a large valve to allow the waste to fall into the lower section.  The upper valve is then closed and sealed.  The lower waste water dumping valve can then be opened from a switch inside the cabin to release the waste overboard.  The lower waste water dumping valve is recessed into the body to keep it from being damaged by rocks.

There are two beds.  One folds down from the left wall.  It is kept raised when not in use to provide walking area.  Above this bed are fiberglass shelves for soil samples and below it is storage for rock samples.  The other bed is mounted forward crossways behind the driving seats.  Storage areas beneath the sleeping bunks hold 70 MRE packages. 

A fiberglass table mounted on the left side, aft corner, forward of the pressure bulkhead, can be used as a soil/rock examination table and holds geologic/biologic equipment: microscope, micro rock saw,

A soil drill is folded along the left outside fitting between the left wheel rock guards and the body.  This drill can be raised and swivel to reach any drilling site within ten feet of the rear of the vehicle.  Swales Aerospace dry drill can go through 10m (32 ft) of rock using only 90 watt's of power.

Raisable communications mast houses two high frequency antennas, and two direction finding antennas.  Mounted on the right rear wheel fairing.

Two driving lights mounted on the upper sides of the forward steel body support band.

Fifteen spare lithium hydroxide canisters for emergency carbon dioxide removal.

Two 175 watt heat lamps work off battery power, through the battery bus, at night to keep the interior warm.  They are positionable and are mounted, one each, near the beds.

There are eight emergency portable spare air containers mounted inside the vehicle, two each near the front, two on the right side mid section, two on the left side mid section, and two in the aft pressurized area.

Small tool/repair kit with following items:
wire cutters and wire splices
mini tubing cutter and tubing flare kit, fittings and extra steel tubing
pry bar
rock hammer
manual soil coring tool
long reach brush to clean dust from solar panels
duct tape
various thin fiberglass panel sizes
thin rubber sheet
extra rubber wheel grips
two extra C02 scrubber fans

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#3 2004-08-05 20:00:03

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,011

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid9]Sounds nice.  Can you link to a picture to show how it all fits together?[/color:post_uid9]


"We go big, or we don't go."  - GCNRevenger

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#4 2004-08-05 20:59:02

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]The closest I have come across is this.  Click on pressurized rover.

http://www.exploremarsnow.org/

My idea differs slightly in that it has an 10' x 18' solar panel mounted above the vehicle, a total of eight hydrogen storage bottles on the outside of the vehicle, solid thin aluminum wheels with rubber grips, only two forward lights, an external soil drill that folds up, a raisable communications antenna. 

My design has a weight problem at the moment.  I'm trying to slim it down.  And trying to figure out it's range, solar (stationary orbiting mirrors included) only provides about 3kw at noon so it would only supplement the vehicles range.[/color:post_uid0]

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#5 2004-08-08 10:24:38

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Hi;

Thanks that you come back to Your Rover. I like it very much. Last time it was not possible to further dicuss a few things due to the strange behaviour of the Thread. I hope You don't mind when I start from this old point again.

Regarding the CFK/GFK-Wheels :  Do You have an link for this sort of Wheels? I was not able to find something myself on the net. Thanks.

Regarding the 4x4 drive:

Propulsion: 4x4 is available but I think they should only use 2 wheel drive as long as it works to save power.  Plus I don't like the motors being built into the wheels, too much vibration, mars dust, and you need some kind of slip ring to transfer the electricity to the rotating wheel.  I still prefer the reduction gearbox idea because it is much more simple.[/quote:post_uid0]

Why do you think the 4x4 drive is only available with motors in the wheel? I wouldn't alter your gearbox-design but would use 4x4 all of the time, but with an intelligent distribution of the load like it is used in modern cars. The Audi Quattro is an good example. Most of the time only the front wheels are in use to preserve fuel, but when the drivers needs 4x4 it works immediately.
I fear that an normal drive is not good enough for mars. The MER rovers for example have to work hard against the slippery soil despite their 4x4 drive. This will be even more of an problem for an bigger and heavier vehicle. So it could be that 4x4 needs less energy than an normal drive.

Regarding the hydrogen-fuelcells:

Water:  I'll have to double check my figures but I believe the fuel cells produce quite a lot of water so the problem was too much rather than not enough.  That's why I put in the shower. [/quote:post_uid0]

Upps. I assumed that you use the hydrogen as an "battery" here being recharged each day from the solar cells; but it seems you use the hydrogen as an fuel only otherwise you would have to make sure that your water is always very clean so the Hydrogen-cells can work at top efficiency all of the time. For me it is a little bit odd to use the hydrogen only as fuel (on mars).
The amount of fuel stored in the Hydrid cells should be enough for an long ride so I think that's ok. With 700lb total weight for the hydrid cells I think the Hydrid itself will be arond 600lb. This 600lb can hold up to 54lb (=9%) of hydrogen when you use the new lithium-hydrid material now in development. This amount of hydrogen can hold 800-880Kwh of energy (not 100% sure if one Kg H2 has 33 or 36Kwh)

So you have around 500Kwh of available energy when the conversion efficieny is ~60% in the fuel cells, enough for >40h continous driving. So the range would be 800 miles @ 20mph.

IMHO one of the big problems with hydrogen fuel cells like the one in development for the Helios UAV is the low conversion efficiency. From electricity to Hydrogen and back to electricity you loose up to 70% of the primary energy. Even when you use highend equipment the combined efficiency of this process is only ( e -> H2 = 80%; H2 -> e = 60% ) 48%  at the most. So even then you loose more than 50% of the energy you capture with your solar cells. IMHO thats not good enough for mars, especially when you take into account the low amount of solar energy available on the surface of the mars.

IMHO you will have to include emerging technology to make your Rover work as intended. The most problematic point seems to be the energy supply so the following to technologies could help you here :

Solar Cells with ~50% efficiency :
http://www.lbl.gov/Science....ll.html
http://www.stp-gateway.de/Archiv/archiv923-e.html

If this sort of Solar cells are developed in time, and at the moment it seems so, then you could generate 2.5 times the electricity per m²

Energy storage with Alu-Accumulators:
http://www.europositron.com/en/techniques.html

Here you can both improve the efficiency of the energy conversion from the 48% with the Hydrogencells to most likely 90-95% with the Accumulators and reduce the weight of the Rover cause the Alu-Accumulators can take over the task of the hydrogen-Storage System and the NiMH-Accumulators in one lighter System.


Manfred[/color:post_uid0]

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#6 2004-08-08 13:27:41

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]I don't think that 4x4 is only available with the motors in the wheel.  This vehicle operates 2 wheel drive, front wheels, most of the time because 2 wheel drive uses less power but the rear wheels (higher gear ratio) can be powered at any time by the driver by simply moving a switch on the drivers console.  I prefer this over the automatic computer controlled four wheel drive because it is simple.  If you need it (deep sand, very rocky terrain, or going up a hill) hit the switch, then turn it off when you don't (moving on a flat surface).  The crew will have laptop computers that connect to the vehicles monitoring system so they can see how much power they are using so it would be easy for them to know whether 2 wheel drive or 4 wheel drive is more efficient.  There is no main computer, other than the crews laptops but they only monitor systems, they do not control them.  The oxygenation/pressurization system has it's own control system.  Really the only disagreement I have with the automatic system is that I believe it adds unnecessary complexity.  It would be possible to add a program (perhaps buy the code from Audi?) on the astronauts laptops that would do what you say but it just seems to me that the astronauts can hit a switch now and then.

The wheels on these habitats and the rover are about what I had in mind:
http://www.nw.net/mars/mars-b3.jpg

I'm a little confused by your next paragraph.  The hydrogen in the storage bottles supplies the fuel cells which combine hydrogen and oxygen to make heat, electricity, and water.  Most of the water is then converted back into hydrogen and oxygen.  One problem is if the fuel cells are used constantly they would go through the entire supply of hydrogen/oxygen very quickly and you would have a lot of water.  The two fuel cells I have in mind are the same as the ones used on the space shuttle.

More info on the fuel cells:
http://inventors.about.com/library/inve … cells1.htm

Now the batteries (batteries=accumulators??) are Nickel Metal Hydride for the most part because they store the most power and because they do not lose anything to cold temperatures unlike other battery types.  I know the new lithium batteries are very promising but larger sizes are still in the development and testing stage and I was not able to find enough information on them to definately put them in this design.  They may improve power storage while reducing weight but can they take the cold?

This design was intended to show that a simple vehicle could be built to do the job and still be relatively inexpensive.  Heck, I could put the whole thing together in my backyard with the help of one electrical engineer.

Yes energy is certainly the critical factor in the success of this design.  The 50% efficient solar panels still seem to be about 10 years away but it would be simple enough to replace the current ones if they were to become available in time for launch.  I knew nothing about the Europositron battery idea.  The website did not give much information other than very high expectations (over 5 times that of lithium-ion???) of power storage.  I'm somewhat skeptical but just as the solar panels it should not be too difficult to include these batteries in the vehicle if they became ready in time.

As to the problem of energy, there are a number of solutions available at this time, none are without problems themselves.  One idea I had is to have mirrors in stationary orbit follow the vehicle as it moves on mars thus providing additional solar power but I doubt this would add more than 1.5 kw to the solar panels.  Another idea someone had was to have a second vehicle with a nuclear RTG power plant follow this vehicle and connect the two at night to recharge the batteries. 

I appreciate your help in perfecting the design.[/color:post_uid0]

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#7 2004-08-08 17:46:36

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]

So you have around 500Kwh of available energy when the conversion efficieny is ~60% in the fuel cells, enough for >40h continous driving. So the range would be 800 miles @ 20mph.[/quote:post_uid0]
The alkaline fuel cells have an efficiency of 70% the other 30% is lost as heat which is necessary to keep the inside of the vehicle warm.  The water created by the fuel cells is then separated back into hydrogen and oxygen by the Teledyne Titan HM-50 system.  I could not find the efficiency of this unit but lets just say it is also 70%.

I believe your figures for the 800 mile range are only for one use of the stored hydrogen and oxygen.  So if you consider that in one complete use of all the stored hydrogen/oxygen you get 800 miles and 70% of that is turned into water and the Titan system converts 70% of that water back into hydrogen and oxygen then you should be able to travel another 392 miles.  Then again, one more pass through of the hyd/oxy and you can go 192 miles.  Then 94 miles.  46 miles.  22 miles.  11 miles.  5 miles.  And a little over 2 and a half.

Actually you will get less distance than this because some of the water will be used by the crew for drinking and maybe a shower once a week. 

Maybe some kind of filter could be used so urine could be recycled??[/color:post_uid0]

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#8 2004-08-08 20:23:54

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Gearboxes are heavy and reduce efficiency.
Wheel - Motor  all inside a large wheel to clear the rocks.
Downhill, it could use regenerative braking to recharge the batteries.
Free help in designing the motor.
-
For emergencies and additional range,
the crew could peddle an exercise bike generator, producing 100 watts each.[/color:post_uid0]

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#9 2004-08-08 21:16:42

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]The gearboxes would be made of lightweight material (thick aluminum or maybe even composite-Kevlar?) but the gearset would be steel.  I think 50 pounds is a good estimate for their weight and is definately not too much.  I dislike placing the motors inside the wheels because they are then exposed to more vibration and shock from climbing over rocks and mars dust as well.  Plus if one fails (like on the Spirit rover) that wheel then becomes a steering problem.

The link you posted shows motors virtually identical to the ones I've chosen for my vehicle except yours are only 97% efficient. 

I'm not familiar with how to make regenerative braking work.  Do you have to install some other component or do the same motors create power from simply turning and send it back through the same wiring they receive power from?  It would go back to the Main AC bus which recharges the batteries.  Not sure how much benefit this would be.

I thought of the bicycle generator idea also but 100 watts would only power a heat lamp and not be enough to turn even one of the electric motors.[/color:post_uid0]

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#10 2004-08-08 21:45:15

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Motor generators are used by railroad locomotives for dynamic braking.
I saw a large diesel electric mining truck with wheel motors.
All cars will soon have them.
-
Gearboxes loose 2% per gear combination.[/color:post_uid0]

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#11 2004-08-09 01:19:17

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]I don't think the regenerative braking would provide enough of a benefit.  It adds weight, cost, and complexity. 

Each gearbox has one combination.  The forward motors turn once and the driveshafts that go out to the front wheels turn eleven times, the rear motors will turn once and the rear wheel driveshafts will turn 7.52 times.[/color:post_uid0]

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#12 2004-08-09 15:27:26

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]For clearance, you are better off without the driveshaft and axle. Additional bearings and power steering mean additional losses and problems. Changing a universal joint is not simple, even in a car.
-
You also need sufficient insulation, enough for body warmth only.
-
The Mars Rovers used 6 aluminium wheel-motors. A heavier vehicle "tire" might be designed with piano wires as the Moon Buggy.

A commercial electric hybrid SUV night be a start for propulsion, just throw away the combustion engine, and add batteries. The Moon Buggy was a General Electric car design.[/color:post_uid0]

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#13 2004-08-09 18:49:27

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]The wheels are 5 feet in diameter and the gearbox is recessed inside the vehicle so ground clearence should be about 2 feet at the bottom most part of the structure.

The driveshafts would connect to the outside of the gearbox and then travel outward to the structure wall where there would need to be a bearing.  Outside the structure wall there would be the universal joint and another shaft that goes to the wheel.  The gearbox is mounted underneath the interior floor which is not a pressurized area.  Access panels below the gearbox and driveshafts could easily be removed to do maintenance.  Changing a universal joint would be a problem but not as much of a problem as changing a siezed wheel motor.  Insulation wouldn't be a problem.

I don't see a need for any more than 4 wheels.

Why would I throw all of this away and start over with a design based on a commercial hybrid SUV?  My idea does more and has more redundancy for mission essential and life support systems plus it's simple, and would be about as inexpensive as you can get.[/color:post_uid0]

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#14 2004-08-10 02:48:46

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Hi Dook;

I don't think that 4x4 is only available with the motors in the wheel.
[/quote:post_uid0]

OK, so this was only an misunderstanding. But I still find it an little bit strange that you don't want to spend the few additional bits and MIPS to support an more sophisticated 4x4 drive. I don't care if it is included in the vehicle or on MIL-Standard radiation hardened Laptops, but IMHO without such an system you will loose an lot of traction and/or energy due to the slippery soil.

I'm a little confused by your next paragraph.  The hydrogen in the storage bottles supplies the fuel cells which combine hydrogen and oxygen to make heat, electricity, and water.  Most of the water is then converted back into hydrogen and oxygen
[/quote:post_uid0]

OK, then forget about this paragraph. Again an misunderstanding from my side. I thought that you would use the Hydrogen only as fuel to feed the fuel-cells and the water supply of the Crew, but would not close the cycle ( H2 -> e -> H2 ). [Also see below]
 

Now the batteries (batteries=accumulators??) are Nickel Metal Hydride for the most part....
[/quote:post_uid0]

Yep at the moment NiMH seem to be the best way, but you should look about other types too. Even if you won't include the Alu-Accu's from Europositron, which I can understand very well, you should at least think about advanced Lithium-Accu's from the company FortuBat cause they already reach around 200-250 Wh/kg with the possibility to reach even 400Wh/kg in the future. The Accu's from FortuBat for example need less than 1/3 the weight and only 40% the volume of an NiMH-Accu to store the same amount of Energy. They promise that the Accu works down to -25°C, so I'm not sure if this is good enough. 

Also if you use Accumulators with such an high energy density you can simplify your Hydrogen System and maybe use the Hydrogen only as an fuel cause the Accumulators would have enough capacity to store all the energy the solar cells supply. This would make it possible to use nearly all of the solar energy instead of loosing nearly 50% due to the hydrogen cycle too. This could be possible with the NiMH-cells too but I'm not sure if the capacity of the NiMH-Accus is high enough. 

I knew nothing about the Europositron battery idea. The website did not give much information other than very high expectations (over 5 times that of lithium-ion???) of power storage.
[/quote:post_uid0]

Yep; so I really hope they can bring this technology to market, cause then Laptops, Handys, PDA's etc...would finally have an decent runtime. smile

The alkaline fuel cells have an efficiency of 70% the other 30% is lost as heat which is necessary to keep the inside of the vehicle warm.
[/quote:post_uid0]

Are you sure? I have only seen one rather unreliable claim of ~65% efficiency for an small fuel-cell until now. Normally fuel-cells with the correct size to suit your vehicle (normally used in cars) have only an efficiency of 50-55%. Only far larger units have an higher efficiency of 60-70% but this are roughly Multi-Megawatt-Units. Smaller fuel-cells always have an lower efficiency than larger fuel-cells.

believe your figures for the 800 mile range are only for one use of the stored hydrogen and oxygen.
[/quote:post_uid0]

Yes, because I was not sure if you would split the water again into H2 and O2 to fuel your Rover.

http://inventors.about.com/library/inve … cells1.htm
[/quote:post_uid0]

Argg... I just read this description. Well that seems to be an really complicated system. They even use 1100 Watt, or maybe up to 50% of the produced energy during low-power conditions to heat the fuel-cells to the correct temperature. WOW imho really inefficient. I was not able to find something about the efficiency of the Shuttle fuel-cells in the document.

Manfred[/color:post_uid0]

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#15 2004-08-10 10:47:01

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]More information on Alkaline Fuel Cells, including efficiency:
http://www.utcfuelcells.com/space/spaceshuttle.shtm

Another reason I didn't use the constant 4 wheel drive is that the front and rear wheels have different gear ratio's.  Not that it would be a big problem but the front wheels are geared lower than the rear wheels to help with hills and climbing over rocks. 

Hmm, tried to find Fortubat on the web but all the sites were in French.

Yes, the fuel cells use and convert a lot of energy to heat but I think this is necessary to keep the inside of the vehicle warm.  The structure of the vehicle will be as thin as possible (maybe 1/2" carbon composite?) and even with insulation the inside of the vehicle is likely to get very cold at night since the only things operating would be the oxygen/pressurization system, the carbon dioxide removal system, and the heat lamps.   

Things I'm working on:
-Trying to find out if the 3 CSIRO motors provide enough power to move the vehicle at the gear ratio I've chosen.
-More exact range taking into account the solar panels and expected power usage by onboard systems.
-A system that filters urine and sends the water to the Titan HM-50 machines to be recycled.
-Maybe remove the shower and the water accumulator?
-Need an exact weight limit for the carbon composite structure and the internal components including the windows, seats, sleeping bunks, internal storage,  science desk,
-Need to lighten it up, 2.2 tonnes is the maximum weight limit.
-Wheel grips need some kind of soft material to cushion the ride.  Thought of making them have a rubber honeycomb interior but the cold temperatures would make the rubber hard as a rock.  Thouht of thin steel bands inside the rubber grips, the steel would bend when the grips drive over something but at mars temperatures the steel would probably just break.[/color:post_uid0]

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#16 2004-08-11 03:19:15

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Dook, this is fascinating. What is the total mass your vehicle adds up to right now? I saw masses of the parts, but not a total.

The vehicle size, 8 feet by 17 feet, sounds about right for a portable hab for several astronauts. Have you looked at the websites of campers, recreational vehicles, and such for design ideas? About a month ago a friend's uncle drove through town in their motor home and I suddenly had a vision of what a Mars vehicle could look like. Since then, every time I drive by an r.v I remember the brand name and look it up on the web. Most of the manufacturer's web sites include floor plans and photographs of the interiors.

        -- RobS[/color:post_uid0]

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#17 2004-08-11 10:33:31

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid14]Beside RV's for a passenger carrying vehicle, Maybe Fuel Cell Bus research is also applicabale. Many have been in use since the early 90's.
We would need to make the fuel cell work with in-situ resources for the bigest bang for the buck.[/color:post_uid14]

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#18 2004-08-11 13:06:50

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Hi;

More information on Alkaline Fuel Cells, including efficiency:
http://www.utcfuelcells.com/space/spaceshuttle.shtm
[/quote:post_uid0]

Thanks! Seems the type of fuel-cell NASA is using in the Shuttle is far more efficient as the fuel-cells used in cars today. But IMHO the efficiency of 70% is only true when the fuel-cell works at 100% power and not at lower power ratings (see my last posting). IMHO you should use the fuel-cell only when necessary to feed the NiMH-accumulators and completely shut down the (thermally insulated) fuel-cells between this "battery loading" action. The Rover would be driven solely from the Accumulators then. With this mode of operation you should get the most out of the stored Hydrogen.

Another reason I didn't use the constant 4 wheel drive is that the front and rear wheels have different gear ratio's.  Not that it would be a big problem but the front wheels are geared lower than the rear wheels to help with hills and climbing over rocks. 
[/quote:post_uid0]

Yes I have seen that, but normally you don't need different gears between the front and rear wheels cause normally (I don't know if this is true for your E-Motors) E-Motors have an very wide and flat torque curve so IMHO it should not be necessary to have different gear ratio's between the front and rear drives.

Hmm, tried to find Fortubat on the web but all the sites were in French.
[/quote:post_uid0]

Sorry the website is only in German or French language. The important link is this one : http://www.fortu.de/punkt07.html. You can see that they promise or guaranty (I'm not sure here) an energy density of at least 200 Wh/kg and promise an further increase to 250 Wh/Kg in the (near?) future.

Yes, the fuel cells use and convert a lot of energy to heat but I think this is necessary to keep the inside of the vehicle warm.  The structure of the vehicle will be as thin as possible (maybe 1/2" carbon composite?) and even with insulation the inside of the vehicle is likely to get very cold at night since the only things operating would be the oxygen/pressurization system, the carbon dioxide removal system, and the heat lamps.   
[/quote:post_uid0]

I don't think that you need a lot of further heating inside the vehicle. Most of the heating will be necessary on the outside to heat all the equipment mounted on the outside. Otherwise it will fail.
The heating of the inside should be fairly easy and simple cause the 2(?) Astronauts alone will heat the inside of the Rover with ~ 2x100 Watt and IMHO the carbon composite will have an very low amount of heat fluctuation if you use Sandwich-Panels with an simple plastic honeycomb "spacer" in between two thin carbon-composite sheets. IMHO this will also lower the weight of the structure cause the highest loading of the structure will surely come from the buckling due to the internal Air-pressure and an Sandwich-Structure can withstand this sort of loading better than an compact structure with the same weight. The only problem with an Sandwich-Structure is that it can debond if the internal Air-pressure in the honeycomb gets too high due to heating; at least that's what happened with the composite-tanks of the failed X33; but the latest test tanks withstand all testing without problems so this problem is solvable. 


Manfred[/color:post_uid0]

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#19 2004-08-11 19:55:18

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]The total mass of my vehicle at this point is estimated to be 5,408 lbs.  I know it's too heavy.  I've been trying to get the weight down but I want each critical system to at least have double redundancy so it's very difficult.  There are some estimates of the actual weights that may be wrong either way.  The structure may not be 900 lbs since it's carbon composite but I have not been able to say for sure yet.  Also I added 1,200 lbs to the above weight for the batteries but I have seen the same NiMH battery combination listed as 1,800 lbs also.

I haven't looked at campers or recreational vehicles because I believe they would have to be greatly modified.  I think this design provides everything a crew would need.  It's simple, relatively cheap, easy to build.  Redundant.  I am not an engineer but I know I could build it in my backyard for the cost of the parts alone.  I would need the help of an electrical engineer and maybe someone to write the computer programs that monitor onboard systems.

Reply to SpaceNut: Fuel cells need hydrogen and oxygen.  Both are included in the mars direct plan.  The vehicles hydrogen and oxygen bottles would be shipped empty for safety then serviced on mars.

Reply to Mboeller:  I agree, the fuel cells would probably be turned on in the morning to charge the batteries then the vehicle operated for a few hours, stop, drill, take soil core sample, lunch, then drive for a few more hours, stop again, soil sample, turn on fuel cell to charge the batteries, then shut it off for the night.

Still debating the different gearing of the forward and rear wheels.  I kind of like it just because if necessary, it's there.  Some parts of mars are incredible rocky.

Heating?  I picked the carbon composite structure primarily to save weight but also so it would transfer less heat.  Mars atmosphere temperature gets down to less than -110 so I'm not sure exactly how hot it would get inside.  It's possible it would get too hot, then I would need to add some kind of cooling system which I really don't want to do since I'm already over the weight limit.  Maybe some kind of aluminum cooling plate that is exposed to the outside?[/color:post_uid0]

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#20 2004-08-11 20:26:26

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid14]Fuel cell Bus should have been written Fuel Cell Powered Buses. In the same token fuel cell research is on the edge with using other gases besides the hydrogen and oxygen.

Sending one tank of each one at a time would be safe enough to do even full. As to shipping an empty set of tanks would it not be better to ship smelting equipment and make the tanks from the Iron rich Martian soil instead.

As for the rechargeable batteries send multiple battery packs to be charged by solar during the day followed by a completing charge as needed by the fuel cells or some other means to charge to capacity before use the following day.

The Mars society research site does have a vehicle that they are simulating such activity with. They may have some insight into some of the details still yet to be fully worked out.

You should be congradulated for the amount of work to which you have done, My hat is off to you.

Good luck getting a prototype built.[/color:post_uid14]

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#21 2004-08-11 23:33:41

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Hydrogen and oxygen are perfect fuels for the fuel cell for a number of reasons.  They make pure water that can be used for drinking and the shipment of those gasses is already included in the Mars Direct plan.

I don't want to send the tanks full, hydrogen diffuses through metals and causes hydrogen embrittlement so the less time the hydrogen is in the compressed bottles the better.  Also if you cannot keep oxygen below -298 it just evaporates anyway.  Sending one tank at a time?  That's against the bible, "The Case for Mars".  There really is no need to have any extra launches.  This vehicle just needs to be fueled when it gets there. 

I do not believe it would be better to ship smelting equipment and make the bottles there but maybe you could do some research and find out just what it would take to do that.

An extra set of batteries would weigh another 1,200 lbs and the vehicle is already overweight.  Sending an additional battery pack is really not necessary.  Solar power is almost useless for this vehicle, it provides a maximum of 1.5 kw at noon.  In the hours before and afternoon, dust storms, and night, it would provide less to none.

There is still some work to do on the idea but it's pretty close.[/color:post_uid0]

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#22 2004-08-12 10:30:19

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid14]Food for thought Alternative power sources being developed.

A New Charge Powering Up New Uses for Supercapacitors.

http://abcnews.go.com/section....-1.html

Snipet:
Like batteries, these devices could hold enough energy to power portable devices, computers, or even cars. And they could be recharged within seconds, not hours like traditional rechargeable batteries.
The heart of Honeywell's solution is a fluorborate salt, a chemical whose physical structure allows it to store a tremendous number of electrons.[/color:post_uid14]

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#23 2004-08-12 11:00:52

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid14]On smelting operations here is a solar furnace.

High Temperature Solar Ovens
http://www.permanent.com/i-ovens.htm

Lunar Materials Utilization
http://www.permanent.com/l-index.htm[/color:post_uid14]

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#24 2004-08-12 13:31:42

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

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]Metalfoam is more stable than carbon composites. A smelter and continuous casting machine could provide structural parts, while the harder to manufacture items would be Earth made.[/color:post_uid0]

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#25 2004-08-12 13:40:44

John Creighton
Member
From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
Website

Re: Simple Mars Vehicle Part 1

[color=#000000:post_uid0]

Metalfoam is more stable than carbon composites. A smelter and continuous casting machine could provide structural parts, while the harder to manufacture items would be Earth made.[/quote:post_uid0]
How do you cast mettle foam? My best guess would be to keep shaking it while it is hardening. You probably would need a mold with a ruff surface too in order for the bubbles to penetrate the surface temperature of the mettle.[/color:post_uid0]

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