New Mars Forums

WOW, You have read my mind.

IMHO DaVinci should stop now. IMO it is ridiculous to go from Zero to 100km in one go without any tests at all. The chances for an successful launch are in my opinion slim. If they don't stop with this stupid behaviour and adopt an reasonable "build a little..test a little" approach they could seriously damage the complete XPrize and the suborbital launch attempts from other companies with an better development strategy.

I don't care if the pilot gets killed or not (this is really up to him) but I fear the reactions of the public and the FAA if this launch goes wrong.

There is no problem at all.

The dock is moving slower than orbital speed, the counter-balance is moving faster than orbital speed and the space station in the middle is moving at orbital speed.

Together the complex of all three parts is moving at orbital speed. So unless you cut the tether the system will remain in orbit just like an normal space station like the ISS.

The added benefit of such an system is, that the docking station is moving (in this example) only at 79% of the orbital speed so you need only around 62% of the energy to reach the docking station. This would make SSTO's very simple and practical (see also the website "affordable Space Flight"). And with the counter balance moving faster than orbital speed you can save a lot of fuel going to the moon, mars or only GEO too when you launch space crafts or just satellites from the fast moving counterbalance. 

Yes, the docking station will drag down the system when an Shuttle docks and nothing is done. But it does not happen fast cause the weight of the shuttle is far lower than the weight of the complete station and you don't need normal fuel to raise the orbit of the system with the docked shuttle. You can use an ion engine instead or even an electrodynamic system to raise the orbit. Just let electricity flow in the tether and the interaction with the magnetic field of the earth will raise the orbit of the station without any fuel.

All in all you don't need a lot of energy for this cause when the shuttle departs from the dock then the orbital system will raise it's orbit from itself and you have only to counter the effect of the payload in the long run unless the payload from and to earth is the same, then (theoretically) you don't need any fuel at all.

I don't think that you need the XPrize to scare the big guys. IMHO they are already (slightly) afraid of SpaceX. SpaceX promises to launch around 4.5 tonnes into GTO for around US $20Mio instead of the around US $80Mio the other companies charge. If they can really fulfil this promise then the big guys will be very afraid.

Hi Dook;

I think I had an idea how you could improve the efficiency of the SolarCells without any new technology:  Use an Heliostat.

See here my idea: http://www.8ung.at/mboeller/Heliostat-S … System.jpg

With this system you should be able to produce max. energy from sunrise till sunset. So instead of the 3 KWh/m² on an flat surface you could produce up to 0,59KW/m² x 12h = 7 KWh/m² or more than 2 times the normal amount of energy. An added advantage is, that the driving direction will no longer affect the energy production, cause the Heliostat will allways face the sun in an opimal way.

The SolarCells here are even a little bit bigger than in Your proposal. So with the (2 x 2x5.6 m² 22.4 m² x 7 KWh/m² x 20% efficiency for the GaAs SolarCells you can generate more than 30KWh per day. Enough for 2 hour of driving at full speed!

I hope you like it.

Manfred

Hi Dook;

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.

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]
 

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. 

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.

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.

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

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

Well at least you can buy an book about the Manna-Machine.

Look here : http://www.fernhouse.com/mannamachine.h … chine.html

Well, I don't want to talk about the strange theories of this guy, but IMHO the technology could really work. In Germany some companies already produce Algae that way, using small but long tubes filled with an Algae-Soup and exposing all that to sunlight. So if you substitute the Sunlight with highly efficient and tuned laserlight (quantum-point lasers are around 80% efficient) then it should be possible to shrink the system down quite a lot. This could make it possible to produce really healthy food in an very compact system. And because of that I mentioned the Manna-Machine as an way to produce (sort of) artificial food.

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:

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:

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-Articles/Arc … ...ll.html
http://www.stp-gateway.de/Archiv/archiv … 923-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/techniqu … iques.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

I don't agree.

IMHO you can use Tethers for much more than an "big" space elevator only, and you don't have to wait for the big breakthrough to get long and perfect nanofibres to make all the other systems work. Most of them work with todays materials or with slightly better fibres. Look at http://members.aol.com/Nathan2go/]this site. Here you can find a few rough suggestions what is possible today without waiting for the future to happen.

I mean, or better Slough means that you need only a 20KW plasma-source to get the same amount of thrust as with an 10MW propulsion unit otherwise. I think he talkes about ion drives here but he does not specify it.

Really? Don't you forget that the M2P2-propulsion has an far higher specific impulse as the simple ion drive like in DS1. You cannot only count Thrust, you have also include the specific impulse here. Slough imho uses an virtual "exhaust velocity" of around 800km/sec or ~80000 sec for the M2P2 [this is an guess, I have not checked the slides, but the equations work] but the DS1 has an specific impulse of only 3000 sec AFAIR.

Theoretically if you would decrease the specific impulse of the M2P2 from 80000 sec to 3000 sec the Thurst would increase from 2 Newton to ~53,3 Newton. This an simple and crude calculation only using the equations Wkin=m/2 * v²  and F = m*v with v= exhaust velocity so the result is not correct but should be in right ballpark.

Sure;

One of the best know Ion Wind Drives was called Ionocraft 40 years ago. Here is an really good description of it :

http://www.rexresearch.com/desev/desev. … /desev.htm

I hope you don't mind the overall source, but this page is IMHO really packed with informations.

Hi Dook;

I still have the old thread "Simple Mars Vehicle" saved on my computer. I can open an new Thread with all the old posting's inside as the first posting if you like.

Manfred

They are already working on self replicating robots for Luna so maybe they will be available when we finally settle on mars :

http://www.niac.usra.edu/?link=mar04_mt … ...ows_mtg

Look for the PDF from Gregory Chirikjian; he has done a lot with his LEGO bricks (!).