ONE SMALL STEP . . .

BillRM said: Off hand I would think that rail guns on the moon would be primarily used to placed materials in near earth/moon space for building projects not for moving humans off the moon into space where the G forces on the cargo does not matter and the rail can be very short.
As Robert Heinlein pointed out in his novel "The Moon is a Harsh Mistress" you better be nice to whoever would control rail guns on the moon as they have what amount to the power of small nuclear bombs that could target anyplace on earth.

What stuff needs to be shot off the moon?

Clarke also says firing nukes from the moon at the earth would be no threat because they'd be spotted on radar coming in from thousands of miles away and be shot down by SAMs launched from earth.

Mike had computed what would happen if a freighter grossing 100 tonnes (or same mass of rock) falls to Terra, unbraked.
Kinetic energy as it hits is 6.25 x 10 12 joules—over six trillion joules.
This converts in split second to heat. Explosion, big one!
Should have been obvious. Look at Luna: What you see? Thousands on thousands of craters—places where Somebody got playful throwing rocks.
Wyoh said, “Joules don’t mean much to me. How does that compare with H-bombs?”
“Uh—” I started to round off in head. Mike’s “head” works faster; he answered, “The concussion of a hundred-tonne mass on Terra approaches the yield of a two-kilotonne atomic bomb.”
“‘Kilo’ is a thousand,” Wyoh murmured, “and ‘mega’ is a million— Why, that’s only one fifty-thousandth as much as a hundred-megatonne bomb. Wasn’t that the size Sovunion used?”
“Wyoh, honey,” I said gently, “that’s not how it works. Turn it around. A two-kilotonne yield is equivalent to exploding two million kilograms of trinitrotoluol . . . and a kilo of TNT is quite an explosion— Ask any drillman. Two million kilos will wipe out good-sized town. Check, Mike?”
“Yes, Man. But, Wyoh my only female friend, there is another aspect. Multi-megatonne fusion bombs are inefficient. The explosion takes place in too small a space; most of it is wasted. While a hundred-megatonne bomb is rated as having fifty thousand times the yield of a two-kilotonne bomb, its destructive effect is only about thirteen hundred times as great as that of a two-kilotonne explosion.”
“But it seems to me that thirteen hundred times is still quite a lot—if they are going to use bombs on us that much bigger.”
“True, Wyoh my female friend . . . but Luna has many rocks.”
“Oh. Yes, so we have.”

Clarke also says firing nukes from the moon at the earth would be no threat because they'd be spotted on radar coming in from thousands of miles away and be shot down by SAMs launched from earth.

I loved that book, but more for the sociological theorizing

http://io9.com/5984371/why-well-probably-never-build-a-space-elevator

To better understand this particular challenge, I contacted Keith Henson, a technologist and engineer who has written about space colonies and related space engineering subjects for nearly four decades. In 1975, he co-founded the L5 Society, now known as the National Space Society. Henson, despite his enthusiasm for space colonization, is skeptical that a space elevator will ever get off the ground.

Why we'll probably never build a space elevator

"No current material exists with sufficiently high tensile strength and sufficiently low density out of which we could construct the cable," he told me. "There's nothing in sight that's strong enough to do it — not even carbon nanotubes."

Indeed, this is the handy piece of evidence that's conveniently touted as the wonder-material that will make space elevators a reality. No doubt, these structures are the strongest and stiffest materials yet discovered in terms of tensile strength and elasticity — a strength that results from the covalent sp2 bonds formed between the individual carbon atoms.

"The best that theorists can do right now is come up with a material that's about two-thirds the strength needed to make a practical elevator," Henson told me. "And that's a very, very short tiny tube."

The problem, says Henson, is that when the carbon bonds get loaded to such an extreme extent, the hexagonal bonds that exist in carbon nanotubes become unstable when converting to 5-to-7 member bonds."

"It's not unlike a run in a lady's stocking," he says.

Henson worries that the cable, when exposed to such a tremendous strain, will simply unzip. Based on some preliminary models, the strain on the tether could exceed 100,000 kN/(kg/m) — so the material will have to have an extraordinarily large tensile strength/density ratio. Even with nanotechnology, he argues, it may not be possible to build material that's strong enough for the job. "It's not immediately obvious what can be done about this," he added.

"The bond strengths are known and you have a very limited number of bond strengths you can use around carbon," he says. "You can go outside of carbon and use boron nitride — it doesn't save you anything in weight — but it would conceivably be more resistant to this unzipping thing." He notes that no one has made nanotubes out of boron nitride.

"So, while it may be theoretically possible to get the material, it still looks pretty unlikely owing to the strengths of the bonds involved... the strength just seems inadequate."

of between 3 and 10 PER LAUNCH due to the fallout from the H3 gas . Sorta like hitting a death lottery

can build elevator cars which till take you to geosynchronous orbit in seven and a half days. Apart from seeming like a rather long time,

How many hundreds of thousands of deaths is likely to occur if the elevator fail after being build?