LiftPort Wants To Build Space Elevator On the Moon By 2020 210
Zothecula writes "When the late Neil Armstrong and the crew of Apollo 11 went to the Moon, they did so sitting atop a rocket the size of a skyscraper that blasted out jets of smoke and flame as it hurtled skyward. For over half a century, that is how all astronauts have gone into space. It's all very dramatic, but it's also expensive. Wouldn't it be cheaper and easier to take the elevator? That's the question that Michael Laine, CEO of LiftPort in Seattle, Washington, hopes to answer with the development of a transportation system that swaps space-rockets for space-ribbons. LiftPort ultimately wants to build a space elevator on Earth, but the company isn't planning on doing it in one go. Instead, Laine and his team are settling for a more modest goal – building an elevator on the Moon by 2020. This is much easier. For one thing, there’s no air on the Moon, so no icing problems. Also, the lower gravity means that no unobtainium is needed for the ribbon. Kevlar is strong enough for the job. And finally, there’s very little in the way of satellites or debris to contend with."
..ok, how? (Score:5, Interesting)
Re:There is one problem... (Score:5, Interesting)
That problem is that there is no way to create a lunar-centric orbit where the upper terminus of the ribbon hovers over a fixed position.
Actually a Lagrange point would do fine for that. L1 is about 58,000 km [universetoday.com] from the moon towards the earth.
Re:The goal of the project? (Score:2, Interesting)
I would imagine so, I can't think of a "killer app" that isn't easier to do with an electromagnetic mass driver, and for exactly the same reasons (near vacuum, low gravity), except for possibly the power requirements.
The 'kicker' of course is that an elevator can't launch heavy rocks at high speeds the way a mass driver can. This protects the Earth from possible terrorrorrorrist takeover of any prospective catapult.
they forgot to do somet math apparently (Score:2, Interesting)
Re:The goal of the project? (Score:5, Interesting)
Indeed, to be stable the elevator would have to be "stationary" within the rotating Earth-Moon frame, with the top extending past either the L1 or L2 point (towards or away from the Earth) far enough that the force of it "falling away" from the moon would be sufficient to counteract the weight of the cable itself.
Calculating the exact distance of the L1 and L2 points can be difficult, but so long as the masses are significantly different they are at approximately the Hills Sphere radius from the smaller mass M2 at r = R (M2 / 3*M1)^1/3. For the earth-moon system that is about 60,000km from the moon, versus the 36,000 km from Earth that constitutes geostationary orbit. So the elevator would have to be about 60% longer than on Earth, but the much lower gravity means it could be far thinner and weaker, and thus easier to build. Even perfect carbon nanotubes barely have the strength-to-weight ratio necessary for an earth-based elevator, with no room for a safety margin.
Plus for the immediate future at least the liability is much lower on the moon - a failure that drops 60,000 km of cable onto the moon from orbit is unlikely to be a problem beyond the fact that your very expensive elevator is now scrap. Drop 36,000 km of cable onto Earth, enough to to wrap almost all the way around the planet, and you're going to have a heck of a lot of secondary damage.
Personally I prefer the idea of the "tumbling cable" elevator - take just a few hundred kilometers of cable orbiting while tumbling end-for-end with the tips coming down almost to the surface like opposing spokes on a wheel rolling along the Moon's equator and you've got an elevator that will match speeds with various points on the equator on a regular basis, coming almost straight down before momentarily stopping and then hauling snagged payload up at roughly 1/4g. By the time the payload reaches it's highest point it will be moving sufficiently fast to easily escape the Moon's gravity, and depending on the particular orbital trajectories of the cable and Moon at the moment of release, moe than enough to escape the Earth's as well, even to put it on a Hohmann transfer orbit to Mars or Venus. Granted all that extra energy means it's not ideally suited to Earth-Moon transfers, but it sure would be a lot smaller and easier to build (except for the necessary drive system to recharge the angular momentum transferred to the payload), as well as making the Moon a major waystation to our much more interesting planetary neighbors.
Re:The goal of the project? (Score:5, Interesting)
Who needs speed? The elevator would still let you drop big rocks on Earth - sure they're moving slow relative to the top of the elevator when you let them go, but the entire moon is moving at about 1,000km/s relative to the Earth, and once those rocks have fallen the remaining couple hundred thousand kilometers to Earth they'll be moving even faster, more than enough to do massive damage wherever they're aimed. We *might* be able to shoot them down, assuming were willing to expend a space-capable nuke against it, were able to hit the thing given the massive speed it's traveling at (shouldn't be *that* hard to basically stand in it's path), and preferred to have radioactive slag come raining down over a wide area rather than letting the rock vaporize it's target. Of course if several rocks were dropped at once that would be far more difficult.
That's the one big problem with a space-based economy - once you're moving heavy stuff around in orbit *everything* becomes a high-yield weapon, and there's not much anyone on Earth can do to defend against it. It's like the ultimate version of trapping your enemy in a narrow canyon where you can fire down at them from all sides. And if an Earth-moon war should ever break out, well the Moon is almost guaranteed victory - both sides will see any incoming weapons a long way out with plenty of time to intercept - but hitting the Moon requires high-energy launches, while launching from the moon requires only ~1/25 the energy (~1/5 the escape velocity) so they can just throw rocks all day long for the cost of launching one missile, and any debris from intercepted weapons in either direction is far more likely to fall back to Earth than hit the moon.