The new double-walled silicon nanotube anode is made by a clever four-step process: Polymer nanofibers (green) are made, then heated (with, and then without, air) until they are reduced to carbon (black). Silicon (light blue) is coated over the outside of the carbon fibers. Finally, heating in air drives off the carbon and creates the tube as well as the clamping oxide layer (red). (Image courtesy Hui Wu, Stanford, and Yi Cui)

A clever new method for making hollow silicon nanostructures produces a battery anode that is not quickly destroyed by the stress of repeated charging and discharging. A hat tip to PhysOrd.com for reprinting this SLAC National Accelerator Laboratory news release written by Mike Ross “New nanostructure for batteries keeps going and going“:

For more than a decade, scientists have tried to improve lithium-based batteries by replacing the graphite in one terminal with silicon, which can store 10 times more charge. But after just a few charge/discharge cycles, the silicon structure would crack and crumble, rendering the battery useless.

Now a team led by materials scientist Yi Cui of Stanford and SLAC has found a solution: a cleverly designed double-walled nanostructure that lasts more than 6,000 cycles, far more than needed by electric vehicles or mobile electronics.

“This is a very exciting development toward our goal of creating smaller, lighter and longer-lasting batteries than are available today,” Cui said. The results were published March 25 in Nature Nanotechnology [abstract].

Lithium-ion batteries are widely used to power devices from electric vehicles to portable electronics because they can store a relatively large amount of energy in a relatively lightweight package. The battery works by controlling the flow of lithium ions through a fluid electrolyte between its two terminals, called the anode and cathode.

The promise – and peril – of using silicon as the anode in these batteries comes from the way the lithium ions bond with the anode during the charging cycle. Up to four lithium ions bind to each of the atoms in a silicon anode – compared to just one for every six carbon atoms in today’s graphite anode – which allows it to store much more charge.

However, it also swells the anode to as much as four times its initial volume. What’s more, some of the electrolyte reacts with the silicon, coating it and inhibiting further charging. When lithium flows out of the anode during discharge, the anode shrinks back to its original size and the coating cracks, exposing fresh silicon to the electrolyte.

Within just a few cycles, the strain of expansion and contraction, combined with the electrolyte attack, destroys the anode through a process called “decrepitation.”

Over the past five years, Cui’s group has progressively improved the durability of silicon anodes by making them out of nanowires and then hollow silicon nanoparticles. His latest design consists of a double-walled silicon nanotube coated with a thin layer of silicon oxide, a very tough ceramic material.

This strong outer layer keeps the outside wall of the nanotube from expanding, so it stays intact. Instead, the silicon swells harmlessly into the hollow interior, which is also too small for electrolyte molecules to enter. After the first charging cycle, it operates for more than 6,000 cycles with 85 percent capacity remaining.

Cui said future research is aimed at simplifying the process for making the double-wall silicon nanotubes. Others in his group are developing new high-performance cathodes to combine with the new anode to form a battery with five times the performance of today’s lithium-ion technology.

In 2008, Cui founded a company, Amprius, which licensed rights to Stanford’s patents for his silicon nanowire anode technology. Its near-term goal is to produce a battery with double the energy density of today’s lithium-ion batteries.

With a clever new method to produce novel nanostructures, a material like silicon, which has been very well studied for half a century as the basis for an important technology, can fill unexpected new roles. A few decades from now, when atomically precise manufacturing provides a general method for making arbitrarily complex nanostructures, we can expect many more surprising developments.
—James Lewis, PhD

Reduced to the max: the emission-free, noiseless 4-wheel drive car, jointly developed by Empa researchers and their Dutch colleagues, represents lightweight construction at its most extreme. The nano car consists of just a single molecule and travels on four electrically-driven wheels in an almost straight line over a copper surface.

… scientists at the University of Groningen and at Empa have successfully taken “a decisive step on the road to artificial nano-scale transport systems”. They have synthesised a molecule from four rotating motor units, i.e. wheels, which can travel straight ahead in a controlled manner. “To do this, our car needs neither rails nor petrol; it runs on electricity. It must be the smallest electric car in the world – and it even comes with 4-wheel drive” comments Empa researcher Karl-Heinz Ernst.

Range per tank of fuel: still room for improvement
The downside: the small car, which measures approximately 4×2 nanometres – about one billion times smaller than a VW Golf – needs to be refuelled with electricity after every half revolution of the wheels – via the tip of a scanning tunnelling microscope (STM). Furthermore, due to their molecular design, the wheels can only turn in one direction. “In other words: there’s no reverse gear”, says Ernst, who is also a professor at the University of Zurich, laconically.

According to its “construction plan” the drive of the complex organic molecule functions as follows: after sublimating it onto a copper surface and positioning an STM tip over it leaving a reasonable gap, Ernst’s colleague, Manfred Parschau, applied a voltage of at least 500 mV. Now electrons should “tunnel” through the molecule, thereby triggering reversible structural changes in each of the four motor units. It begins with a cis-trans isomerisation taking place at a double bond, a kind of rearrangement – in an extremely unfavourable position in spatial terms, though, in which large side groups fight for space. As a result, the two side groups tilt to get past each other and end up back in their energetically more favourable original position – the wheel has completed a half turn. If all four wheels turn at the same time, the car should travel forwards. At least, according to theory based on the molecular structure.

To drive or not to drive – a simple question of orientation
And this is what Ernst and Parschau observed: after ten STM stimulations, the molecule had moved six nanometres forwards – in a more or less straight line. “The deviations from the predicted trajectory result from the fact that it is not at all a trivial matter to stimulate all four motor units at the same time”, explains “test driver” Ernst.

Another experiment showed that the molecule really does behave as predicted. A part of the molecule can rotate freely around the central axis, a C-C single bond – the chassis of the car, so to speak. It can therefore “land” on the copper surface in two different orientations: in the right one, in which all four wheels turn in the same direction, and in the wrong one, in which the rear axle wheels turn forwards but the front ones turn backwards – upon excitation the car remains at a standstill. Ernst und Parschau were able to observe this, too, with the STM.

Therefore, the researchers have achieved their first objective, a “proof of concept”, i.e. they have been able to demonstrate that individual molecules can absorb external electrical energy and transform it into targeted motion. The next step envisioned by Ernst and his colleagues is to develop molecules that can be driven by light, perhaps in the form of UV lasers.

Despite any shortcomings as far as practical transport across a surface, this achievement is remarkable in that the nanocar is not moved by being passively dragged across the surface by the STM tip, but rather the STM tip delivers charge to four functional units, inducing in each a conformation change that causes the movement. The motion they observed—six nanometers after ten steps—is almost exactly what they had predicted from theoretical considerations.

Dear Nanodot,

Zyvex Technologies announced that its 54-foot‚ boat named Piranha completed sea trials near Puget Sound in the Pacific Ocean and demonstrated record fuel efficiency. After six months of extensive testing, the Piranha this morning completed its final sea trial; a 600-nautical mile, rough-weather test in the Pacific Ocean in Washington and Oregon.

Piranha finished the tests in time to travel to its debut at the Sea Air Space show in Washington, DC, on April 11th. There, defense contractors are evaluating the Piranha for use as an unmanned platform with a variety of mission applications, including anti-piracy, harbor patrol, and oceanographic surveying

A conventional aluminum or fiberglass boat would have consumed 50 gallons or more per hour, while test results prove that Piranha consumed only 12 gallons of fuel per hour while cruising at 25 knots. The Piranha demonstrates Zyvex Technologies‚ ability to produce products with nano-enhanced materials that are 40% stronger than metals, such as aluminum, and 75% lighter, resulting in increased fuel efficiency.

Zyvex produced Piranha in just 90 days. The makers believe it can help coastal city leaders in ports like Seattle, San Diego, Miami, Norfolk, and New York better protect their harbors. In 2009, the New York City Police Commissioner testified before Congress that even with the Coast Guard’s assistance, the department could not fully protect the harbor, especially considering the vast amounts of uninspected cargo that enters the Ports of New York and New Jersey, pointing out that Mumbai was just another reminder. Two years later, there is still an urgent need for better port and maritime security.

The recent Oman piracy tragedy for four Americans from Seattle underscores the need for additional civilian and commercial security. In addition to the U.S. Navy, unmanned surface vessels such as Piranha can be deployed by Customs and Border Patrol, Port authorities and harbor police in high risk areas. Pirates can be tracked over long ranges with a clear picture of location so commercial vessels can avoid them. Piranha is an alternative to costly aircraft carriers. With its range and endurance, military personnel could remain on station for weeks and still protect designated areas. Piranha can be leased as an escort for commercial or private sailors through dangerous areas.

Jackie
For Zyvex Technologies

For more, Piranha completes rough weather sea trials. See also PRWeb and at Zyvex Technologies.

To participate or listen-in remotely:

Kindly send an email to me at j.winter@eurospaceward.org if you would like to participate or listen-in remotely to our conference this weekend.
Kind regards,
John Winter

Hot air ballooning is quite popular today; people think of balloons as being quaint and pretty and natural, or at least more natural than airplanes.

Actually, a modern hot-air balloon uses more fuel than an airplane does to fly the same payload for the same time. The reason, of course, is that hot air needs to be hot, but the balloon needs to be light, so that the material needs to be thin, which means in practice that heat is lost through the balloon, and needs to be regenerated by burning fuel.

With nanotech we could make a fabric of diamond sheets for strength, with vacuum for insulation, and thin metallic films (or graphene sheets) to reflect thermal radiation. That means that we could have a balloon that was much lighter than woven nylon, and yet enormously better insulated.

The air in a balloon may be typically heated to around 100C, making it 0.93 kg/m^3 (compared with 1.2 at 20C). Call it roughly 0.25 kg/m^3 lifting capacity.

But if we can insulate it, we could fill it with steam instead (at the same temperature). (Steam would condense on the walls of an uninsulated bag.) Steam at 100C has a density of 0.59, call it 0.6 kg lifting capacity. Since we aren’t losing heat (much), we could superheat it and get some extra lift, say a few 0.1kg/m^3, but there would likely be a tradeoff with insulation weight, energy rates to cover leakage, etc. Even without it, the balloon lifts its own weight, including the water in the steam (and probably 100 times that of just the balloon).

(Postscript: It’s occasionally assumed that diamond is strong enough to make air-buoyant vacuum-filled balloons. This doesn’t actually work. Hydrogen remains the champ, with a density of 0.09 kg/m^3, which is essentially negligible. But even so, a steam balloon would only have to have twice the volume of a hydrogen balloon with the same lift, as compared to 5 times for hot air.)

If the tower you build is shorter, you’d fall, since (a) you aren’t going quite as fast, and (b) orbital speed is faster as you get lower. However, you’ll be in some orbit. There should be some height, short of GEO, where the ellipse you follow doesn’t quite hit the earth. We can use the Vis viva equation and some algebra to see what that height is:

Vertical scale is kilometers per second, horizontal is kilometers height above the earth’s surface.  The green line is for a circular orbit, blue for an ellipse that just misses the surface. The red line is the speed of the top of a tower of that height (at the equator).

For the blue line, elliptical orbit, you’ve saved a lot of tower height but it’s still pretty darned tall.

Suppose, though, you use a tower to launch rockets from.  It’s well understood that you save a lot by not having to punch through the atmosphere, but you can also save a lot from the height and speed of a tower of intermediate height.  The real savings shows up because of the exponential nature of the rocket equation, as we can see from the chart of the mass ratio needed in a rocket from the tower-tops:

(For a typical chemical fuel) The red line represents the part of the rocket that is the payload, and the other lines tell you how many times payload mass is the total vehicle mass.  The difference is fuel you need.  They cross, of course, at the same heights as stepping off works and no fuel is necessary.  The knee of the curve (blue is still elliptical) is only about one earth radius (~6400km) high, a tower we could actually build with nanotech materials, where you only need about 3 payload masses of fuel to get to orbit instead of nearly 20.

Flying cars – or personal aircraft anyway – have moved a step nearer, as ongoing trials using robot aeroplanes and next-gen air traffic equipment in America are said to offer the option of “reduced crews” on commercial cargo flights.
US aerospace firm GE Aviation has been participating in joint trials with the Federal Aviation Administration (FAA) aimed at letting unmanned aircraft fly safely in civil controlled airspace, Flight International reports. An early option offered by the technology is the prospect of reduction from two pilots to one on commercial cargo flights.

The tests involved passing of traffic-control instructions to a Shadow roboplane, a type normally used by the US Army in warzones where civil rules and traffic aren’t an issue. Generally, air-traffic controllers give instructions to pilots by voice: nowadays, rather than translating these instructions into action via joysticks, throttles etc the pilot will simply key commands into an automated flight management system (FMS).
The next logical step is to remove the needless waste of bandwidth inherent in voice comms and the error potential and delay that comes with an on-board human pilot and his fingers. Orders can be passed directly to the FMS – in this case, part of the Shadow’s ground control station rather than on board, but with the same effect on the craft’s manoeuvring.

So, how close are we to flying cars? For specificity, let’s pick a technological bar to hurdle that answers most of the objections to the concept we’ve seen as comments on the previous posts:

• It should be relatively high-powered compared to current light craft.
• It should be STOVL for safety and convenience.
• It should be quiet enough to operate in residential neighborhoods.
• It should fly itself, without piloting from the passengers.
• It should be self-maintaining.
• It should be inexpensive enough for widespread ownership.

Now I claim that current technology is, more or less, up to the first 4 of these. But the corner of the technological envelope that we are pushed into in order to satisfy them makes the last 2 that much harder.

Flying cars are a really good example of the sort of Jetson’s futuristic world that nanotech and AI together could enable, but would be essentially impossible without both. They are something that’s right on the edge of what’s possible with current technology, but current technology falls short in three crucial areas:

Power

Although Maxim arguably built a steam-powered flying machine in the 1890′s, practical powered flight had to wait for the gasoline internal-combustion engine. By WWII, piston engines had been pushed to the limit, and the second half of the 20th century saw serious flight powered by gas turbines. In optimal regimes (e.g. at high altitudes where the air is really cold) and at high compression ratios, the Brayton cycle can get up to 50% thermodynamic efficiency. This is quite good for a heat engine on Earth but with a eutactic molecular mill that didn’t thermalize the potential energy we could get close to 100%. (Fuel cells fall somewhere in between.)

I won’t speculate on specifics, but there are enough alternatives being explored that it seems likely that we may be able to replace not only heat engines but chemical fuels sometime in the coming century. (OK, I’ll mention a couple: stimulated alpha emission from long-lived radioisotopes, or proton-boron to triple-alpha fusion/fission. These produce energetic charged particles which convert directly to electricity without needing a heat engine.) Advances like this could be of as much benefit in the twenty-first century as the IC engine was in the twentieth.

Intelligence

Most of the actual advances of AI you hear about these days is about laboriously constructed programs that get better and better at various tasks, slowly approaching human performance (e.g. at driving cars). Most of the futurist hype you hear is about superintelligence erupting and taking over the world. As you can readily imagine, the reality of future AI will be somewhere in between.

The major difference between AIs today and those of ten years from now will be that the future ones will be able to learn skills on their own that must be added now by extensive, and expensive, programming. That means that the ability to fly a car — and to maintain one — will be learned as a human would, so it’s robust in the face of unexpected situations. Flying-car AIs, like all AIs, will exchange experiences and techniques. Each one will be as expert as any one. In the medium term, this will be the major impact of AI: that expertise equivalent to the world’s best will be available cheaply to all practitioners.

Manufacturing

Futurists such as H. G. Wells managed to forsee everything about the automobile except the single, but crucial, fact that everybody would be able to have one. But that is the fact that made all the difference. In the twentieth century it was Henry Ford and mass production that was the enabler; in the twenty-first it will probably be nanotech and autogenous manufacturing. This is easiest to understand in economic terms: the price of things depends on productivity, which in turn depends on capital replication rates. That doesn’t necessarily mean the time it takes a factory to make another physical factory, so much as for a factory to make stuff worth what it cost to build the factory.

This is why nanotech scaling laws are so important. Operation frequencies scale with the inverse of size, so bacteria reproduce in hours while humans take decades. Harnessing this productivity accelerator into the industrial loop means that costs of physical goods — particularly high-complexity high-tech goods — can begin to fall along the Moore’s Law curve we already see for electronics.

Bottom line: A flying car with the flight envelope I talk about could be built today but it’d cost a million bucks. One with all the capabilities you’d want will be available in 10 years, but you’ll still have to be rich to get one. Flying cars for the masses will be technically and economically possible in 20 years, if the political will is there to let it happen.

How close to a true VTOL does a flying car have to be to retain the advantages we would like?  If you have to keep it at an airport, you have to drive there and back in a separate vehicle, obviating many of the advantages.  If it can fold up its wings and drive around town, like the Terrafugia, it gets most of them back. (The alternative is the modular convert-a-plane, where you leave the wings at the airport.)

Yet there remain a number of reasons why you might want to be able to takeoff and land anywhere. The landing part is obvious: safety. If the vehicle can come in for a soft landing more-or-less straight down, it doesn’t need to get close to things like houses and people while moving at highway speeds. Luckily, an apparatus which can do that quietly and efficiently was invented back in the Renaissance by Leonardo da Vinci: the parachute. Some small aircraft actually have whole-vehicle emergency shutes today; it seems reasonable that various combinations of chutes, wings, and high-lift devices (flaps, etc) could be invented that would be deployed for takeoff and landing and folded for high-speed flight. A STOVL car might, for example, be able to takeoff from a straight stretch of road, or from your driveway if it were long enough (mine is), and land anywhere, which would make it enormously more convenient than having to operate out of an airport.

Convenience aside, there is another reason to want a VTOL vehicle. The more power you have in a plane, the safer. Storms, wind shear, clear air turbulence, even airliner wakes can toss small craft about and crash them.  Power is safety — and of course power is speed, as well.  So in the long run, you would expect flying cars to tend toward VTOL.

And it doesn’t have to happen all at once.  If you have a thrust equal half your weight, for example, you can get to 40 mph in a 100-foot takeoff roll, and then have plenty of oomph to shove low-stall-speed high-lift devices through the air, and still climb at about a 30-degree angle.  There would be room for lots of takeoff runways in the average suburb, any mall parking lot, and so forth.

There is, of course, a catch. In modern technology, VTOL means noisy.  Helicopters are considered annoying 20 decibels quieter than street noise, because of the whup-whup nature of their characteristic sound. Small plane props are quite loud as currently used, and if you put enough of them, and enough power into them, to take off vertically, they’d be hellacious. Ducted jets like the Harrier, and rockets, are earsplitting.

On the other hand, the actual wind noise (as opposed to the rotor noise) produced by a helicopter taking off is a not particularly noisome whoosh. So it is physically possible to throw down a column of air that will lift a car-sized vehicle in a non-objectionable way, if you can find some way to generate the column quietly.

One possible answer is to use lots of small thrusters instead of a few large ones. Lots of small motors also have a reliability advantage in that they only lose a small fraction of their total power when one fails. In current technology, this isn’t seen because many small motors are much more expensive (to make and maintain) and not as efficient as one big one.  However, if we imagine some steps along the Feynman Path so that we have a high-precision microtechnology, we might be able to get into the increasing power-to-weight regime of electrostatic motors to decreasing scale. Then all we need is good fuel cells.