Aerovator, Angel fleet, Polywell

[ciphergoth]

Ideas that are currently entertaining me:

• The Aerovator: a spinning wing 2,000km long whose tips rise 100km up and travel at 8 km/s which unlike the Space Elevator can be built (just) with today's materials.
• The Angel fleet: Counteracting global warming with a fleet of 16 trillon solar shades in space between the Earth and the Sun (we can use the Aerovator to put them up)
• Polywell fusion which if it turned out to be possible would save the world - plus we can power the Aerovator with it.

Comments

[purplerabbits.livejournal.com]

I wish I could believe in feasible fusion power, cos I don't see any other way of powering the Angel Fleet that won't cause more glabal warming...

[ciphergoth.livejournal.com]

The linked paper does talk about that:

The environmental impact of launch must be considered in addition to its cost. In the worst case, if electrical energy were generated with coal, {approx}30 kg would be required for each kg transported to L1. But each kilogram of the sunshade mitigates the warming effect of 30 tons of atmospheric carbon, a thousand times more. Note that if the launch were by rockets with kerosene/liquid oxygen fuel, the carbon consumed would be comparable. It takes {approx}20 kg of kerosene to place 1 kg in low-Earth orbit with an efficient two-stage rocket (9), and likely twice this to escape the Earth. On the other hand, the fuel cost for rocket launch is much higher. Kerosene costs currently $0.73/kg, compared with {approx}$0.02/kg for coal delivered to power stations. This difference underlies in part the economy of magnetic launch.

I think the Aerovator would be more efficient still, but in the baseline configuration that's powered by 747s pushing it along.

[purplerabbits.livejournal.com]

Hmm. Given that it's 16 trillion of them you might want to take account of the fuel used to make, transport and support the process from the ground, including the global warming produced by concrete for building the new launch base etc etc.

It's not impossible, but it would indeed be a bit of a last resort...

[nik-strychnine.livejournal.com]

I'm rather concerned by the prospect of atmospheric vortices being shed by the big wing...

...but still, science is cool!

[ciphergoth.livejournal.com]

The wing spins about once every thirteen minutes...

[ciphergoth.livejournal.com]

Each one weighs just over a gram - it probably takes about as much carbon to make the fleet as it does to make, I don't know, 20 million tons worth of toys or laptops or whatever. What's the most-made thing in the world, I wonder?

[meico.livejournal.com]

Artifical diamond?

[meico.livejournal.com]

Eck! Misread your question... I interpreted it as the most carbon producing thing to make...

In answer to your actual question... I would think it would be something "disposable". Maybe plastic bags? Loo roll?

[martling.livejournal.com]

> which unlike the Space Elevator can be built (just) with today's materials.

"Just" concerns me. If it's only just got the tensile strength required, then it should work in still air, but add in the weather and the resultant additional strains and subsequent oscillations on the wing, and you'll get tension peaks popping up all over the place.

With drive/drag systems distributed all along the wing you might be able to compensate for this to keep the loads evenly distributed, but that woudl add a whole lot of complexity to the structure.

However my main concern would be the ability to actually design a suitable wing. In most aircraft the limiting factor on airspeed, propulsion aside, is not the sheer force on the wings, but flutter: aerodynamic forces combined with elasticity in the structure leading to oscillation.

See here (http://www.youtube.com/watch?v=mxFOHoy-UNQ) for this occuring in practice in a flight test. The pilot increases the speed just enough to induce the flutter, then backs it off. If he took it too far, positive feedback would kick in and the wing would break up.

[akicif.livejournal.com]

Hmmm. 13 minutes to move the tip approximately 6300km is going to spin off quite a lot of fast-moving air: it's about 24x the speed of sound at sea level.

Also, 240 tonnes in 1000km is 240 kg/km or 240g/m - at a specific gravity of 1, it would be well under an inch across, so we're talking quite a thin piece of material.

Naw, sorry. it's either bullshit or a spoof.

[ciphergoth.livejournal.com]

But the tip is at 100km, where the air is so thin that it doesn't even count as being in the atmosphere.

Yes, I think it's meant to be very thin for much of its length.

It may well be bullshit, but it's not a spoof - the guy who named it has put a lot of work into it...

[ciphergoth.livejournal.com]

I wouldn't be surprised if this were the sort of problem that killed the idea - the guy who writes it has thought through issues about tensile strength etc but he's pretty open about his ignorance on complex matters of aerodynamics. Still, there's some hope that the sheer length of the wing would actually reduce the impact of problems like this, the way tall buildings are better at surviving earthquakes...

[martling.livejournal.com]

The high tension combined with the length does intuitively suggest a longer wavelength of oscillation, but I'm not sure if that means the forces involved will be any less severe.

One thing I do know is that subsonic, transonic and supersonic aerodynamics are three very different things, and that one of the big problems with designing supersonic aircraft is coming up with a shape that works for all three regimes. Whether you could accomplish all three with something that's basically just a ribbon, and be able to actually bootstrap the rotation, I have no idea, but it sounds tough.

[drdoug.livejournal.com]

Cool! (Doubly so.)

We could do with a bit of appropriate techno-optimism.

Saints alive but that aerovator is going to move a lot of air. Obviously most of it isn't in 'air' but the bit that is will make a Big Ass Fan look like a nanopropellor. And siting something that big will be a slight challenge politically - for scale, the radius is roughly the distance from London to Berlin, or the length of Califonia.

I love the bit in the Angel fleet paper where they explain away two or three orders of magnitude of cost-per-kg for lifting stuff off the earth by assuming the existence of yet-to-be-prototyped transport technologies, the development costs of which are negligible.

If I've understood it correctly, in terms of development, polywell fusion is a decade or more behind tokamak fusion ... which is about forty years from commercial deployment (and has been for about the last forty years).

[ciphergoth.livejournal.com]

It would pretty much have to be sited in some unused part of the Pacific. Though it's 1000km in radius, most of it is so high up that you wouldn't care - shipping wouldn't have to avoid that region or anything. What worries you about moving that much air?

Guns have been prototyped eg SHARP. The development costs are negligible compared to the $2 trillion cost of building and launching the fleet. I'm sort of hoping it can be made more cheaply than that - for one thing, the Aerovator would allow the disks to be larger.

The encouraging thing about Polywell is that the problems may be substantially easier, because their containment is more straightforward, and the reactors are much faster to build, so it may yield a working commercial reactor long before DEMO first sees plasma.

[drdoug.livejournal.com]

The air moving is more a wow than a worry - tho it might mess with Hadley cells or jetstreams something. I can imagine airliners wanting to keep well clear.