Space elevator for surface transport

Two weeks ago I was at Space Access '13 and ran into Michael Laine, since when I've been thinking about novel uses for a Lunar Space Elevator.  I've come up with one for which a few minutes of searching could turn up no prior art, so I'm publishing it here lest some troll try to patent it.  I'm still trying to think of a snappy name for it, and you can help.

How it works

The easiest way to describe it is as a tetherball with the main elevator cable in place of the central post and a vehicle in place of the ball.  For the tether we'd use some more of the material we used for the main cable, and we'd need some kind of swivel at the place where the tether and post met.  The tether would be longer than for a playground tetherball, long enough to reach ground level with a bit to spare; the vehicle would contain a winch that could reel in enough tether so it (the vehicle) would hang at or slightly above ground level.  By some means of propulsion that might range from a push with a stick to a high-velocity rocket thruster, the vehicle would start itself moving away from the main cable, and would reel the tether in to lift itself up to clear any obstacles, then out again to descend to ground level and land at some distance from the main cable, if a landing were desired.  If the mission were to survey the surface near the main cable without landing, then when the vehicle had almost come to a stop, thrust would be applied at right angles to the direction of travel to send it on a circular or elliptical path around the main cable.  An elliptical path will precess, so that the vehicle could survey the interior of a circle centred at the main cable, rather than just the circumference of such a circle.

Ready for some snappy names?  The ones I've thought of aren't very snappy: lunar pendulum, Tarzanator, non-o-rail.  Suggestions welcome!

Energy and time

The equation for a pendulum with a rigid, massless rod under 0.16 of an Earth gravity gives, for a length of 10km, a period of oscillation about 490 seconds, so we could travel from the main cable to the end of the swing in 123 seconds, just over two minutes (journey time would be independent of distance traveled, up to a point -- if you don't believe me, ask Galileo).  I think the speed at the bottom of the swing is pi/2 times the average speed, so to travel 1km would require a starting speed of nearly 13 m/s; a ballistic launch at the same speed 45 degrees above the horizontal would give a parabolic flight that would last some 11 seconds and travel some 100 metres, so the pendulum travels further for the same amount of energy, and can have a softer landing with no extra fuel, but it is still subject to a square law: for a given length of tether,  twice the distance means four times the energy.  If we want to travel further without using more energy, we have to go slower. Making the tether 1,000km long gives a journey time of  roughly 1,225 seconds, so for the same starting speed we could travel 10 km, or for ten times the speed (a hundred times the energy) we could travel 100km.

I should not have used that equation, because the tether is neither rigid nor massless, though if it is made of a fibre such as Kevlar and is no thicker than it needs to be, well, OK, let's give a safety factor of 2, then a 1,000km tether will have about as much mass as the vehicle (including its payload).  But giving a sudden push to a heavy weight at the bottom of the tether would lead to a lot of energy being wasted in lateral oscillations of the tether: Twang!  Plausibly we could fix this by accelerating the vehicle over a time comparable to the time it takes the lateral wave to reach the top of the tether.   I estimate the speed of a lateral wave along the tether at 1km/s, so a cautious acceleration time for a 10km tether would be about 10s, which is small compared to the journey time; for a 1,000km tether I get 1,000s, and for longer tethers the acceleration time would exceed the journey time, so it seems that long tethers don't offer much advantage.

The tether would tug on the swivel and cause lateral oscillations in the main cable.  These are already a problem for space elevator designs, and I don't propose a solution here; I hope somebody develops one.

Economics

The pendulum could be constructed together with the main elevator cable and would need little additional technology development, so the cost should be modest.  For a young Lunar settlement it could provide occasional point-to-point transport and obviate the need to design and construct some ground vehicles and roads, which would require more tech.  As the settlement grew, a road, rail, or tunnel system would be added to provide more capacity than a pendulum.

Further applications

On Mars, where there is enough wind to provide thrust, a vehicle with a sail could travel modest distances with no input power; how it could achieve a trip upwind is left as a exercise for the reader. There are obvious applications to deploying instruments in the upper atmosphere of Mars, at altitudes below the reach of satellites but above that of balloons.

If a terrestrial space elevator were constructed, a pendulum carrying a current would be magnetically pulled eastwards or westwards from the main cable, and could mount a defence against space debris.

The ability to suspend a moving mass from a space elevator implies that launching from the elevator into a circular orbit may become possible, for a wide range of heights and inclinations, using a low-thrust engine.  A vehicle circling about the elevator cable would impose a hefty oscillating lateral load at the swivel; this could be overcome by adding a counterweight, but there may be other problems.

Harare on the Potomac

Books like Why Nations Fail make clear that many a third-world country stays poor not because its government is having difficulty thinking up policies that would help it get richer, but because the government's members or supporters would be inconvenienced if those policies were carried out.  The Harvard Business School asks companies why they prefer not to create jobs in the USA, and finds that the complexity of the tax code is an important factor (see figure 14 on page 19).  So why is the tax code so complex in the USA?  Wouldn't it be convenient for everyone, not just companies, if it were radically simplified?

Well, nearly everyone.  But it's hard to shake companies or people down for campaign contributions by threatening to take away their tax breaks, if they don't have any tax breaks for you to take away.  So now we know who is inconvenienced.

Making Corruption Work FOR The People

[from my Google+ stream]

I was going to write something about money in politics, but thought I'd better give credit to an earlier article that had provided the germ of my idea. Fortunately, I remembered enough words to search for it and find it. Turns out it contains all of what I had fondly thought to be my idea. It's even more relevant today than it was eleven years ago.

Crediting the Voters: A New Beginning for Campaign Finance

Change technology, change society?

Arthur Dobrin had this to say about Mitt Romney, well, ostensibly about him, but more about creative destruction.  The core of Dobrin's argument seems to me to be not very much about economic models, but about innovation. Selected quotes:

> Innovation is the way of capitalism.

> This is all to the good if the extent of the destruction is the replacement of one product with another (the TV for the radio).

> You cannot support both unleashed capitalism and a stable social order. Along with new products come new ways of doing things; along with new ways of doing things come new ideas.

It sounds as if Dobrin is saying that innovations in products can lead to changes in society, more profound than just exchanging one product for another or one employer for another. I suppose one obvious example is the Pill. Thus promoting innovative businesses is at odds with conserving society, and someone like Romney should not, with a straight face, claim to be a social conservative.

The question of what responsibility falls on an innovator as a result of the social changes his/her products bring about, or on the society that benefits from those products, does seem to me to be important. Gov. Romney is not the one on trial here; the whole idea of unrestrained innovation is being examined.

eating gamma rays

I would have rejected this as impossible until the day I read it in Science News. It reminds me of a ghastly blurb for one of Hal Clement's books asserting that "in science, nothing is impossible!" I still feel sure that plenty of things are impossible ... but not necessarily the things we thought were impossible.

In case you have trouble with the link, a quick summary is as follows: a fungus has been found that actually harvests energy from gamma rays, using the well-known pigment melanin. Do not try this at home.

Who cares about warming

Global warming is going to take a long time, but could be very costly if it happened the way some people expect, and yet, it's hard to estimate the probability that it will happen that way, given the evidence we have now.

So, logically, we should entrust our precautions against it to an organisation that knows how to plan for events that are uncertain, long-term, but very costly. Definitely not a political party ... we know how long-term they think ... much less an environmental pressure group, because they treat all propbabilities as either 1.0 (if it's something they want us to be frightened of) or 0.0 (if it's not frightening enough) ... but such organisations do exist, and have existed for a long time, and many of us know them, though few of us love them.

Have you guessed yet?

That's right: insurance companies. And they're making a difference.

Myths about heroin addiction

This one is simply wonderful. Read the first two or three paragraphs if you are short of time. One-line summary: bureaucracies usually perpetuate the problems they set out to solve. Well, there's a good deal more, and all of it good, talking about how people really become addicted and why they really stay that way (summary: they have nothing better to do or to be), but the beginning is the most widely applicable part. If I were writing the article, I might risk my skin by pointing out that the same applies to many other organisations who claim to be fighting one kind of evil or another.

I've found a fair amount of good stuff elsewhere in TheAustralian especially in the Books section.