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Comment by throwanem | Hacker News Reader

Because it's easier to build a reusable rocket than a reusable railgun, especially a reusable railgun that's hundreds of kilometers long.

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Easier solutions aren't necessarily good. Rockets are extremely dangerous and expensive.

The ~200km required is daunting, but imminently possible.

Many things are possible. But military experiments on a scale four orders of magnitude smaller have revealed many previously unsuspected engineering difficulties with putting the technology into production. Solving those problems at the 20m scale would seem a necessary prerequisite to successfully building a space launcher at the 200km scale.

Pointing your rail gun up is best for getting out of the atmosphere ASAP, but how do you build a gun that goes, say, 20 km high into the air?

A mostly (the curvature of the earth will make it point up) horizontal gun will have the problem that the projectile will leave the gun at escape velocity, at around 1 atmosphere of air pressure (either after accelerating through 1 atmosphere of air pressure, which takes lots of extra energy, or leaving a vacuum, which makes exiting the gun barrel quite a bang)

Also, your barrel will have to extremely straight.

I don't think either is 'imminently' possible.

Pointing your rail gun up is best for getting out of the atmosphere ASAP, but how do you build a gun that goes, say, 20 km high into the air?

It's physically possible for us to build a 100km tall tower with current technology. (Columns formed from many highly pressurized tanks made from boron.) It's not really economically feasible, however.

I wonder how well such a tower would withstand the forces involved in also launching projectiles at escape velocity.

As of around the year 2000, I remember a figure of 11 miles as the height limit for a fairly conventionally built skyscraper. If we used lightweight truss construction, I suspect we could build a load bearing tower. If we used aerospace grade materials, we could do even better. (Yes, it would be quite expensive.)

Quite expensive like "a significant portion of the annual gross global product"

Most of the load could likely be mitigated by wings and buoyant structures.

Most of the acceleration track floats between San Cristobal (Galapagos Islands) and Ecuador. Near the end, it ascends Mount Chimborazo to 6000m and punches through a plasma window separating only 0.46 atm external air pressure from the low vacuum inside the accelerator.

At our current level of technology, I estimate this would cost at least $200 billion in capital expenses.

A neutral-buoyancy under-ocean train between two cities otherwise un-connectable by terrestrial transit would prove some of the necessary technologies. Liverpool to Belfast would probably work. Miami to Havana to Cancun would work, if not for politics.

Relevant search terms: "vactrain", "StarTram", "transatlantic tunnel"

You'd be better off putting that money into space elevator research.

I was just explaining how possible it is. I am skeptical that anything like it will ever actually be built on Earth.

Other non-rocket launch technologies do seem more promising. If you could build a mass driver launcher between Galapagos and Ecuador, you could likely build a launch loop in the same spot for less capital, less operating cost, and higher capacity.

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