The quick refresher – a Dyson Sphere is an idea to encase the sun in a ball to collect the whole solar energy output.  There are problems – one is if all the matter in the solar systems was used and made into a material at about steel’s density it would be about 8cm or a little over 3 inches thick at a radius of 1 AU – but that’s too close, it would soon melt.  To get to a low enough temperature the sphere would have to get at least 1.6 AU out – then the material is insufficient to self-support at steel’s strength.

Then moving the sphere – to keep the sun orbiting in the galaxy centered would consume practically all the power output.  The Dyson idea while ambitious remains impractical.

Brian Wang at NextBigFuture caught up to a pdf file and paper abstract that explores an idea based on the Dyson idea called the Dyson-Harrop satellite (DHS). The modeling of such a device pops some big energy gathering numbers.  Brooks L. Harrop and Dirk Schulze-Makuch  at Washington State University published this idea in the International Journal of Astrobiology.

A DHS could be built – a 1-kilometre-long wire and sail 8400 kilometers wide could generate roughly 1 billion billion gigawatts (10^27 watts) of power, which is 100 billion times the power humanity currently requires.  Time to sit up and take notice of orbital solar power?

But all that power has a drawback as well. To beam power from a Dyson-Harrop satellite to Earth, one “would require stupendously huge optics, such as a virtually perfect lens between maybe 10 to 100 kilometers across.”

A DHS would be relatively cheap to construct, given that the system is composed almost entirely of copper and doesn’t require circuitry.  As Wang points out in his narrative, “Later versions could use carbon nanotubes (when they are cheaper and made in higher quantity) for lighter wires that can handle more current.”

A DHS is actually a simplistic, self-sustaining system that draws power from the solar wind and uses a laser to fire energy to collectors (on space stations, bases, etc.) positioned anywhere in the Solar System.  The DHS draws energy from the solar wind’s electrons, using the Sun’s high-energy photons only to eject the electrons once their useful electronic energy has been collected.  That means the electrons out there are collected which can’t get through the atmosphere and the much lower energy photos are used to keep the collector clean.  Physics can be marvelous sometimes.

Dyson Harrop Satellte Function. Click image for the largest view.

Here’s how it works.  Looking at the diagram above you’ll see the Sun (A) emits plasma half-composed of electrons, half of protons and positive ions (B).  Electrons are diverted via the Lorentz force from a cylindrical magnetic field (C) from their radial trajectory towards the ‘Receiver’ (D), a metallic spherical shell. When the Receiver is “full”, excess electrons are diverted through the hole in the Sail. The large positive potential on the Sail drives an electron current through the ‘Pre-Wire’ (E), which is a long, folded wire designed to cancel out the magnetic fields of the current towards the Sun. Once it reaches the end of the Pre-Wire, it travels down the ‘Main Wire’ (F), creating the magnetic field (C), which makes the field-current a self-sustaining system. The current passes through a hole in the Receiver and then through the ‘Sail’ (G), passing through the ‘Inductor’ (H), and the ‘Resistor’ (I), which draws off all of the electrical power of the Satellite to the ‘Laser’ (J), which fires the electrical-turned-photonic energy off to a designated target. Drained of its electrical energy, the current continues to “fall” to the Sail (G). Here, electrons will stay until hit by appropriately-energetic photons from the Sun, at which point they will leap off (K) from the Sail towards the Sun, and then be repelled by the magnetic fields (C) and excess solar wind electrons (B) away from the Satellite, imparting kinetic energy to the Satellite away from the Sun.

A bit complicated – but way elegant and self-position supporting as well.

Because the magnetic field diverts positive particles away from the satellite and electrons toward the Receiver, the DHS remains virtually untouched by excess solar wind particles. And since the satellite ejects electrons when their current cycle is complete, even large satellites have a minimal impact on the Sun’s solar wind output.  Plus the kinetic energy from the photoelectrical ejection of electrons from the Sail provides a strong stabilizing force; in fact, it may be possible to design a satellite that can remain in a stationary position.

Sounds great – the other hand holds some major problems that could well be solvable. The DHS isn’t very efficient so its big, then so is outer space.  Being so simple and large, protection from that high-speed stuff out there is a major concern.  Staying in position while seemingly designed in has to be engineered and work.  Then the DHS doesn’t self-start – a pre charge to get it in a self-sustaining cycle needs to be provided.  Finally the DHS is going to get hot – shedding the heat is going pose an engineering task of considerable significance.

These all seem to be solvable problems, but there is one more.

One DHS could fully power humanity’s needs if the power could be brought down.  Various transmission ideas are working, but so far nothing really seizes attention as a great way to get the power down here.

When such a space energy collection system exists, the orbital photovoltaic projects will need a rethink.  Meanwhile, so much power so cheap can be its own lure. Its not such a giant leap to imagine that life off planet is much more practical if the DHS is made fully workable and redundantly reliable.  That makes ideas like life off planet would be the main while the life on the planet itself would be a privilege or a resort kind of thing.

The resources out there are stupendous and with cheap energy at hand the idea of getting to them is quite alluring.  The DHS concept is certainly one to watch – the numbers are simply too good to ignore.


7 Comments so far

  1. Matt Musson on September 28, 2010 8:16 AM

    Brian, Maybe with the recent discovery that carbon nanotubes are twice as strong as previously believed – we will have a space elevator soon. Then this Dyson sail could become a reality.

    Btw, did you see the Chinese have embargoed Rare Earth Elements to the Japanese? No more Toyota Prius’ or Wind Turbines until that gets resolved.

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