I would like input and ideas on a low gravity high-speed train for the moon.

Some issue I would like input on include;

Power source
Car size
Rail material and form
Limitations
Consideration of environmental issues


Any relevant links would be welcome.

Would it need a power source? If you use a magnetic levitation rail (maglev) it would move without any drag because there is no air. So, one could simply give it a gentle push and it would slide towards its destination at a constant speed.

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My cyncicism (and possibly the second law of thermodynamics, im not sure) suggests that isn't the case.

I'd have to ponder it further, but I think the acceleration due to gravity (as the moons pull made it go over the curved surface instead of a straight line) would be where you would lose energy.

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OK, I have to add that it takes a horizontal stretch of rail for this to be true.
However, if it is horizontal relative to the Moon's gravity field, the curvature of the Moon doesn't induce any acceleration. On a rail all around the Moon the train would run forever. I think. Maybe the moving magnetic fields induce a little current and thus take kinetic energy away from the train?

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Well, there is still some drag, it's not a perfect vacuum there. It might run a good long time with a push, but not forever. Presumably, this train will also need to start and stop, and even if the kinetic energy is captured when it stops and reused to accelerate it again, there would be less than perfect efficiency. The main issue I think would be that the passengers would find the stations relatively inaccessible, since they are all on the moon.

How can this be the case? Anything that has no acceleration acting upon it moves in a straight line, and a train passing over the surface of the moon moves along a curved path. It must be accelerating.

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In a gravity field a straight line is a conic section. Like a planet orbiting the Sun does so in an ellipse. The planet does actually accelerate but the sum of its kinetic and potential energy remains constant and therefor it stays in the same orbit. Now, our train is of course not in free fall around the Moon, but I don't see how it can 'lose' energy as long as there is no friction with the rail. Maybe a good analogy is a roller coaster. I think you can build interesting roller coasters on the Moon!

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I think a snow train type craft is a great idea. A lot of heavy equipment already uses electricity here. Check out Caterpillers equipment.

http://www.bigfoot4x4.com/more5.html
http://movingnorth.blogspot.com/2005...imate-suv.html

Another reason to support Sea Dragon. Several launches could put that up there.

Cugel has already provided an explanation, I will offer a slightly different (but entirely compatible) perspective. The train is constantly accelerating; if the speed of the train is exactly equal to the orbital velocity just above the moon's surface, the force that generates the acceleration is the moon's gravity, at any other speed it is a combination of the moon's gravity and a force generated by the mag-lev or whatever it is system. However, the direction of this force is always perpendicular to the motion of the train, assuming it is running on "flat" terrain, where "flat" means very slightly curved, forming a perfect circle around the center of the moon. (Ugh, I guess if it is on the moon, it's not "terrain"? What should it be called? "Lunain?") In this case, the force does no work, so there is no expenditure of energy, anymore than a table expends energy when it keeps an object from falling.

Edit - Cugel's explanation is better. Just ignore this one...

Power Source: Either a nuclear power station that would already be feeding other locations, or a large solar farm also already feeding other lunar projects.

Car Size: I can't be specific but you would need them to have shielding against outbursts of intense solar radiation and of course extensive and redundant life support systems.

Rail Material: Titanium. In the Sea of Tranquility is a vast supply of Titanium in the soil. You could use it for making the cars on the surface, too.

Environmental Issues: ??? What environment? We're talking a completely dead world with no atmosphere. As long as you don't add appreciably to the surface radioactivity then you have nothing to worry about.

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I have my doubts on solar energy because most places on the Moon 'enjoy' a 14 day long night.

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If you could use super-conductive cables, you could have
solar energy farms all around the Moon, and provide power 24/7.

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I suggest that given the low gravity and vacuum resistance to movement will be minimal anyway. The gain in efficiency of magleve over metal wheel would probable not justify the increased complexity of the rail. Or maybe it would.

Revision: My apologies. I beleive that wheels would impose a limit on speed that maglev would not.

How about a nuclear power plant on the train? How about orbital power stations that could beam power down with microwaves? I wonder if hydrogen fuel cell would work out. Good point. I had forgotten about the radiations issues. Perhaps a subway then. I would say the cars should be quit large given the low gravity though stability will be an issue and since there is no air they could be any shape, maybe inflatable spheres.I did not know this. Interesting.I meant the life support and living conditions in the train.

Consider orbital mirrors or orbital power station that beam power. The trains schedule could match the solar cycle since there are no clouds it would be predictable.

What would a train be used for on the Moon?

City or base on the moon. One massive train city or perhaps an array of trains that make up the city. Some trains would go collect resources, explore, space vehicles could be launched at high speed and perhaps retrieve in a similar fashion to save fuel. Trains could move to avoid detected meteor impacts. Perhaps circular banked tracks to make a train centrifuge. Trains would lay and repair track. If all the structures are mobile they offer great flexibility in accommodating expansion and changing missions.

There is no friction with the rail, but it is applying a downward force to the rail, correct?

I'm not sure that what works for orbits would work for a maglev.

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Correct. The train's weight is applied to the rails, even if it hovers above it.
The passengers will not be weightless either, as they would be if the train went into orbit. Maybe we should forget the 'orbit' explanation all together, this is purely a case of energy conservation. If there is no friction the kinetic energy of the train can ONLY be transformed into potential energy (by climbing a hill for instance). This potential energy will be transformed back into kinetic energy (=speed) when the train goes down hill again.

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The train pushes the rail into the ground. Work is done, energy is lost from the train surely?

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If the rail doesn't move no work is done. If the train (or anything) is standing still it is still pushing its weight against the floor, isn't it? But it is not doing any work. (Work is defined as the product of the vectors force and change of speed dW = F . dS)
If the rail does move, you are right, energy is lost.

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