What if you have an enclosed track in a partial vacuum that runs up along a mountain and exits where the air is thinner? Everest is 8.8km tall, and air at that height has 1/3 the pressure as at sea level [1]. If you can build a 1km tower on top to extend the track, you can get down to 1/4 the pressure.

[1]: http://www.engineeringtoolbox.com/air-altitude-pressure-d_46...

Sounds like a modified hyperloop

No doubt that's true in the individual case, but surely you'd attempt to run a "train" into the atmosphere with this kind of thing? Meaning that each projectile is slipstreaming behind the one in front.

It still might not be possible, but it seems like friction would be much less of a problem. Although starting up would be a significant issue with many thousands of projectiles hitting earth at high velocity - you'd want to run it 24x7 indefinitely.

That doesn't sound like a low cost project, though; certainly well beyond our current capabilities. But you might achieve very nice energy efficiency with it.

This is my imagination vs your imagination, so neither of us really has anything resembling an argument, but I'm wondering if in such a scenario the following projectiles might not find themselves running into the plasma wake left by the preceding projectiles. As such, your scenario might actually be worse than firing things one at a time.

The plasma wake will be less dense than the atmosphere displaced by the leading projectile, but it'll be much hotter and comprised of [#] much heavier atoms.

[#] "comprised of" is a correct usage, for anyone sucked in by the poor guy obsessed with editing it out of Wikipedia (many words have opposing meanings and some great English poetry depends on this; the term causes no confusion amongst native speakers; etymology is irrelevant to modern usage...)

>[#] "comprised of" is a correct usage, for anyone sucked in by the poor guy obsessed with editing it out of Wikipedia (many words have opposing meanings and some great English poetry depends on this; the term causes no confusion amongst native speakers; etymology is irrelevant to modern usage...)

The tyranny of the minority, in this case, is comprised of a single man, whose idiosyncratic reign of grammatical terror is now reaching out from Wikipedialand into the Greater Internet.

I find this all very amusing.

In my mind, I'm picturing this being used to shoot pretty much blocks of solid materials, not anything delicate, so the only issue is how much they are slowed down; by the time we could build something like this, fabricating in space is not going to be an issue.

Of course, by the time we could build this (assuming its even possible), mining asteroids could already have surpassed it.

This could maybe be an xkcd "what if" problem....I suspect a train of mach 27 projectiles would have some interesting effects on our atmosphere.

But why can't we use the railgun to replace just the first stage of a rocket? Due to the tyranny of the rocket equation that would mean outsized savings in fuel and payload.

It would be exiting the barrel at far less than mach 27 so this wouldn't be an issue.

Even without a first stage, wouldn't that mean that the railgun would need to account for dealing the energy needed to accelerate a couple hundred thousand tons of rocket fuel to any reasonable speed? As per Newtons 3rd law?

This is correct. And the power needed for larger rockets is well beyond what we currently generate with traditional power plants on earth.

For instance, the space shuttle with SRBs and SSME's firing would require more than five Hoover Dams to match (11.7 gigawatts, vs 2.074 gigawatts). The Three Gorges Dam puts out 18.3 gigawatts, but the Saturn V first stage did somewhere around 190 gigawatts.

You could get away with less of course, since with rockets the first stage must lift the immense mass of itself, but with a railgun you will have significant efficiency losses with all of the energy conversions involved. I would expect a heavy-lift railgun to consume at least a significant percentage of a large nation's entire power supply. So we'd be looking at ludicrously sized capacitor banks, or some very large power plants that sit idle without anything to do while we aren't launching rockets.