Originally posted by twhitehead
I don't think it needs to be too serious a vacuum. There is talk of using the air in the pipe to support the carriages (air bearings) as well as having powerful fans in the carriage to move air from the front to the back - and there have even been suggestions of using that for propulsion.
The main thing stopping trains from going faster is air resistance ...[text shortened]... one packed in like sardines which would save on infrastructure costs. But nobody would use them.
Have you seen anything from Musk about propulsion? It seems to me linear motors would be more efficient than fans. And the better the vacuum the less the drag and the less air has to go around the vehicle.
One thing, it seems to me the thing would have to be powered by electricity powered by fuel cells or batteries since there would be no air to use in reactive devices. I assume therefore it would have to be some kind of battery which would mean it would have a pretty short range no matter what propulsion is used. Air bearings require a constant flow of air and at a pretty high pressure too.
We use an air bearing assembly in one of our computer test sets, it has an X Y linear motor for X and Y movement held off the linear iron drivers by air pressure so it slides around under electromagnetic control, and it has a Z axis for the probes, up and down a few mm for contacts of dozens of almost microscopically tiny probes. Very delicate probes I might add, the probe assembly costs 3000 dollars and they go out quite a bit. I know, I destroyed on accidentally once🙂
Anyway I don't think air bearings would work very well in that system. Think about how much drag there is even in a plane at 100,000 feet up. My guess is they would need a vacuum better than that if they wanted the speed advertised.
The main drawback, assuming a real vacuum in the minus 6 range would be the range since it would have to be driven by electricity and you can only keep so much in the way of batteries onboard. But with a high enough vacuum it could have a pretty significant range, much better than anything running at full atmosphere.
If we ever get cities on the moon, they will have linear motor trains that will go a lot faster than 800 klicks since there is almost zero atmosphere and a good source of sunlight most days.
I envisioned a trans-lunar railway going only 16 or so klicks powered by a huge array of solar cells atop the train, say a couple klicks long and able to send power into the tracks besides moving from station to station, 24/7, it goes around the moon every 28 odd days and stays always with the sun overhead so it has always got the full 1400 watts per square meter, and of course by then they will have 70% cells🙂 so it supplies power to a large number of urban centers, a hundred megawatts sent by the room temperature superconductors which will have been developed then, which will have a junior version of the martian magnetic shield, a few turns around the lunar equator making a nice mag field which will protect the citizens. When they prove it works on Luna they start doing the same for Mars and then crash a few small comets onto Mars to generate an atmosphere.
Hey, it could happen🙂