[extropy-chat] lunar elevator

[Damien Broderick]

>
>Perhaps moon based manufacturing launched  by mass driver or space elavator.

I'd been under the impression that a lunar elevator wouldn't work; it'd be 
too long or something. However I see another view at

http://www.universetoday.com/am/publish/lunar_space_elevator.html

<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 
<http://www.m5fiber.com/magellan/m5_fiber.htm>M5, 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 [all] 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 >

etc. Less orbital junk, harder for crazies to damage it, run it with 
robots, etc.

Damien Broderick