Hear Hear.

However I suspect that the construction metal of choice for space industrialisation, despite its weight, is likly to be Iron.

Dusty

Good points Googlenaut.

Particularly about the need for heavy lift capability.

OTOH, I recall reading (see below) that the space elevator could perhaps be developed in a sort of boot-strap mode :  First would be a lunar elevator, which could actually be deployed from a single spool, if its initially only sized for small payloads ( < 1 tonne). The small payloads can be used to bring up more material (perhaps just to support the L1 station crew and propellant for their shuttle craft), and/or additional spools can be brought in from earth to gradually increase the number of strands making up the elevator cable....  Once this system matures, materials can be supplied to the construction of an earth elevator -- initially perhaps just a "rotavator," followed later by a full-scale GEO version. Think of it as the narrow-gauge railway systems of the 19th century, that were eventually replaced by today's standard railway gauge....

As for the possibility of using material from Near Earth carbonaceous asteroids, I belive that Dennis Wingo, the author of "Moonrush," got it right when he said that we have a better chance of finding the required materials on the moon, which has been "collecting" all sorts of asteroids on its surface for hundreds of millions of years -- whereas NEA's are very few & far between, and rarely made of useful types of materials (question: do we know presently of even a single carbonceous-type NEA ?  .....the same question could certainly be posed about locations of specific carbonceous NEA debris sites on the moon, but the point is that in this case the search is limited to a sigle location -- the moon -- with well-defined acessibilty requirements....).

Summary - (Nov 18, 2004) Science fiction writer Arthur C. Clarke famously predicted that we'd see space elevators 50 years after people stopped laughing at the idea. Jerome Pearson has been thinking about space elevators since the early 1970s, and he's been watching the growing enthusiasm (and fading chuckles) with great interest. But he knows there are significant challenges in engineering and materials that still need to be overcome, so he's suggesting NASA build an elevator on the Moon first. And the agency is taking the idea seriously.

Full Story - A speech by Arthur C. Clarke in the 1960s, explaining geostationary satellites gave Pearson the inspiration for the whole concept of space elevators while he was working at the NASA Ames Research Center in California during the days of the Apollo Moon landings.

"Clarke said that a good way to understand communications satellites in geostationary orbit was to imagine them at the top of a tall tower, perched 35,786 km (22,236 miles) above the Earth," Pearson recalls, "I figured, why not build an actual tower?"

He realized that it was theoretically possible to park a counterweight, like a small asteroid, in geostationary orbit and then extend a cable down and affix it at the Earth's equator. In theory, elevator cars could travel up the long cable, and transfer cargo out of the Earth's gravity well and into space at a fraction of the price delivered by chemical rockets.

... in theory. The problem then, and now, is that the material required to support even just the weight of the cable in the Earth's gravity doesn't exist. Only in the last few years, with the advent of carbon nanotubes - with a tensile strength in the ballpark - people have finally moved past the laughing stage, and begun investigating it seriously. And while carbon nanotubes have been manufactured in small quantities in the lab, engineers are still years away from weaving them together into a long cable that could provide the necessary strength.

Pearson knew the technical challenges were formidable, so he wondered, "why not build an elevator on the Moon?"

On the Moon, the force of gravity is one sixth of what we feel here on Earth, and a space elevator cable is well within our current manufacturing technology. Stretch a cable up from the surface of the Moon, and you'd have an inexpensive method of delivering minerals and supplies into Earth orbit.

A lunar space elevator would work differently than one based on Earth. Unlike our own planet, which rotates every 24 hours, the Moon only turns on its axis once every 29 days; the same amount of time it takes to complete one orbit around the Earth. This is why we can only ever see one side of the Moon. The concept of geostationary orbit doesn't really make sense around the Moon.

There are, however, five places in the Earth-Moon system where you could put an object of low mass - like a satellite... or a space elevator counterweight - and have them remain stable with very little energy: the Earth-Moon Lagrange points. The L1 point, a spot approximately 58,000 km above the surface of the Moon, will work perfectly.

Imaging that you're floating in space at a point between the Earth and the Moon where the force of gravity from both is perfectly balanced. Look to your left, and the Moon is approximately 58,000 km (37,000 miles) away; look to your right and the Earth is more than 5 times that distance. Without any kind of thrusters, you'll eventually drift out of this perfect balancing point, and then start accelerating towards either the Earth or the Moon. L1 is balanced, but unstable.

Pearson is proposing that NASA launch a spacecraft carrying a huge spool of cable to the L1 point. It would slowly back away from the L1 point as it unspooled its cable down to the surface of the Moon. Once the cable was anchored to the lunar surface, it would provide tension, and the entire cable would hang in perfect balance, like a pendulum pointed towards the ground. And like a pendulum, the elevator would always keep itself aligned perfectly towards the L1 point, as the Earth's gravity tugged away at it. The mission could even include a small solar powered climber which could climb up from the lunar surface to the top of the cable, and deliver samples of moon rocks into a high Earth orbit. Further missions could deliver whole teams of climbers, and turn the concept into a mass production operation.

The advantage of connecting an elevator to the Moon instead of the Earth is the simple fact that the forces involved are much smaller - the Moon's gravity is 1/6th that of Earth's. Instead of exotic nanotubes with extreme tensile strengths, the cable could be built using high-strength commercially available materials, like Kevlar or Spectra. In fact, Pearson has zeroed in on a commercial fibre called M5 [http://www.m5fiber.com/magellan/m5_fiber.htm], which he calculates would only weigh 6,800 kg for a full cable that would support a lifting capacity of 200 kg at the base. This is well within the capabilities of the most powerful rockets supplied by Boeing, Lockheed Martin and Arianespace. One launch is it takes to put an elevator on the Moon. And once the elevator was installed, you could start reinforcing it with additional materials, like glass and boron, which could be manufactured on the Moon