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The problem with a manned pressurized exploration vehicle is a power source.
-Solar doesn't do much for you since mars is so much farther away from the sun. You would need solar panels the size of a basketball court.
-Hydrogen fuel cells would get you maybe 400 miles.
-Nuclear would provide enough power but the power plant would have to be heavily shielded and towed behind, far behind, the vehicle.
What if a series (3?) of mylar space mirrors were spread out and placed into a stationary orbit over a mars base and used to reflect light from the sun onto a 1/4 mile area surrounding the exploration vehicle? The mirrors would have to follow the vehicle as it moved but could provide enough sunlight to reduce the solar panels to maybe 10' x 18'. Not sure how large each of the mirrors would have to be though.
Also when the mirrors were not supporting the vehicle they could be used to increase the amount of sunlight on the mars base solar panels as well as the domes that are growing crops.
As more mars bases are built mirrors would be placed into stationary orbit above each. Over time and with enough mars bases these mirrors would essentially be terraforming mars.
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Various means of distributing beamed energy might be from towers and mountain tops.
Military beamed weapons are capable of focusing on a small object. Similar techniques would provide flexibility.
The equivalent of a Martian exploration vehicle might be a billboard sized solar collector, mounted on wheels. High power, when in sight of the power distribution network, but still able to operate from sunlight.
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Why not use high-capacity batteries that charge at the base?
I'm no mechanical/electrical engineer, but would that be a huge problem?
For longer trips, the vehicle crew could bring along a roll up or fold up solar panel or something and let it recharge for several hours while they are working.
Implementing big orbiting mirrors to track vehicles seems like a LOT of extra effort, not to mention expense.
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I wish my simple mars vehicle post hadn't froze again. I may post it again (third time) but this time cut it up into three posts to keep that problem from happening.
The fact is a 26 module NiMH battery set would weigh 1,200 pounds and provide 6.8kw of power to propel a pressurized vehicle for maybe 4 hours at a speed of 20 mph. It's just not going to get you very far plus once you get there you are completely out of power to operate life support systems.
A group of galium arsenide on germanium solar panels measuring 10' x 18' mounted on top of the vehicle would provide only 1.5 kw at noon. Not much to really do anything.
There really is no easy solution. Zubrin prefers combustion engines but they consume a lot of fuel. A 1 liter, 67 hp methane/oxygen engine would use about 174,000 cu in of methane/oxygen a minute. If you were to carry the oxygen/methane in 8 compressed cylinders (435 cu ft each) it would give you about 34 hours of travelling time.
The neat thing about the mirrors is that they would not have to be very large (a couple hundred feet square?) and they could augment the base's solar panels when not supporting the vehicle as well as provide extra lighting for the crops growing in the domes. And their orbit would have to be stationary, just like geo-synchronous satellites on the earth, for them to be of any real use.
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It almost sounds like coming up with a shielded micro-nuke reactor would be better.
You sure there's no better/lighter batteries around?
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New idea for the mirrors:
The best way to describe it is that when the mirrors deploy the system would look like the fingers on your hand spreading out with large suction cups mounted to the fingertips. There would be a central tube to house the communications equipment that locks onto the vehicle as it moves and also be a small rocket motor to raise the mirrors orbit.
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The small nuclear reactors are a great source of power but they would require a lot of very heavy shielding and have to be towed far behind the vehicle.
The NiMH batteries, in my opinion, seem to be the best for mars. They provide a lot of power, as far as batteries go, and are not as affected by cold temperatures as the other battery types.
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The small nuclear reactors are a great source of power but they would require a lot of very heavy shielding and have to be towed far behind the vehicle.
Wait a moment... isn't that perfect?
Maybe slightly unwieldy, but just make 2 nearly identical vehicles. One is the crew vehicle, and the other is the power source vehicle. The power source vehicle is simply remotely controlled by one of the crew. All they need to do is steer it along behind them at a safe distance and recharge every few hours. Mobile power plant--they don't need to worry about getting stranded without power.
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Hmm. Actually that sounds like a pretty darn good idea. The power source vehicle could be a simplified design and if necessary a cable could be hooked up so either vehicle could tow the other.
Only drawback is that it would have to come on another launch though. You could have the manned exploration vehicle go first and use it for relatively short trips around the base and then when the nuclear powered one arrives you could take off and survey the planet. No orbiting mirrors needed.
An 80kwe (more than enough) reactor weighs 3.5 tonnes, the rest of the vehicle I estimate at 1,500 pounds, structure, suspension, electric motors and drivetrain, that's 5,000 lbs total. Too heavy. I believe the weight limit allowed is 2.2 tonnes if you count the pressurized rover and do not include the 2 open rovers. There's gotta be lighter nuclear reactors out there. Definately do not need 80 kwe for a rover.
Reference:
The Case for Mars, pg 93
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An 80kwe (more than enough) reactor weighs 3.5 tonnes, the rest of the vehicle I estimate at 1,500 pounds, structure, suspension, electric motors and drivetrain, that's 5,000 lbs total. Too heavy. I believe the weight limit allowed is 2.2 tonnes if you count the pressurized rover and do not include the 2 open rovers. There's gotta be lighter nuclear reactors out there. Definately do not need 80 kwe for a rover.
Yeah, it might be useful to investigate how small/light of nuclear reactors we can get down to... 80kw is WAY more than enough, I'm pretty sure 1/10th of that, 8kw would be plenty for this sort of situation.
Unless of course we're talking some BIG rovers... then it might be ok to have something this big, but still that's a lot more power than is needed.
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Approximate solar cell power estimate:
http://powerweb.grc.nasa.gov/pvsee/publ … insolation available = 3 kW-hr/m2 per day
A 100 m2 averages out to 12KW.
Pulling a large solar array or several would be sufficient.
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Pulling a 100 meter square solar array across the surface of mars??? Hmm, I would rather have the second vehicle with the nuclear reactor.
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Maybe 4m X 25m would be more convenient.
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A large, towed, unpressurized box could be paneled with solar cells,
serving the double purpose of carrying extra parts and supplies.
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Could work. If you put a 10' x 17' solar panel on top of the vehicle (see my simple mars vehicle idea) you could then reduce the towed solar array to 4 meters by 20 meters.
The disadvantage in this case would be that you would primarily operate in the daytime or at night for a limited amount of time on fuel cell and/or battery power.
With an RTG you can operate at night just as much as in the daytime.
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Approximate solar cell power estimate:
http://powerweb.grc.nasa.gov/pvsee/publ … insolation available = 3 kW-hr/m2 per day
A 100 m2 averages out to 12KW.
Pulling a large solar array or several would be sufficient.
IMHO you have forgotten to include the efficiency of the solar cells. With GaAs-Cells with ~20% efficiency you would need around 500m² for the 12 KW.
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The average solar intensity at the orbit of Mars is 590 W/m2
You are right.
0.59 KW/m2 X 0.2 X 100m =11.8 KW
But less than half, due to night, and the array is not aimed.
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