Isegoria

There are no known commodity resources in space that could be sold profitably on Earth, Casey Handmer explains:

On Earth, bulk cargo costs are something like $0.10/kg to move raw materials or shipping containers almost anywhere with infrastructure. Launch costs are more like $2000/kg to LEO, and $10,000/kg from LEO back to Earth.

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Let’s consider a representative list of the most expensive materials in the world. In descending order, they are:

• Antimatter, currently $62.5t/g.
• Californium, $25m/g.
• Diamond, $55k/g.
• Tritium, $30k/g.
• Taaffite, $20k/g.
• Helium 3, $15k/g.
• Painite, $6k/g.
• Plutonium, $4k/g.
• LSD, $3k/g.
• Cocaine, $236/g.
• Heroin, $130/g.
• Rhino horn, $110/g.
• Crystal meth, $100/g.
• Platinum, $60/g.
• Rhodium, $58/g.
• Gold, $56/g.
• Saffron, $11/g.

The previous ballpark estimate for transport costs was $100,000/kg, or $100/g. Since I want to be inclusive, I’ll include everything down to saffron in the list above, whose cost is roughly equal to the current LEO-surface transport cost.

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None of the products represent large markets, due to their prohibitive price or relative scarcity. As a result, they are subject to substantial price elasticity depending on supply. For example, the global annual market for Helium-3 is about $10m. Double the supply, halve the price, and the net revenue is still about the same. No-one seriously thinks that Lunar mining infrastructure can be built for less than many billions of dollars, so even at a price of $100,000/kg, annual demand needs to exceed hundreds of tons to ensure adequate revenue and price stability.

Tritium, helium-3, platinum and antimatter represent speculative future markets, particularly where increased supply could help develop an industry based on, say, fusion, exotic batteries, or a bunch of gamma rays. If fusion-induced demand for helium-3 reaches a point where annual demand has climbed by three orders of magnitude, then I am willing to revisit this point. But current construction rates of cryogenically cooled bolometers are not adequate to fund Lunar mine development, and solar PV electricity production has every indication of destroying competing generation methods, including fusion.

Some relatively expensive minerals are only expensive because low levels of industrial demand have failed to develop efficient supply chains. If demand increases, new refining mechanisms are invariably developed which substantially lower the price. A salient example here is rare platinum group metals.

Space-based solar power is not a thing, Casey Handmer argues:

As Elon Musk has concisely pointed out, the fundamental problem with space-based solar power is that it’s obtaining a commodity, power, somewhere where it’s expensive and selling it somewhere where it’s cheap. This is not a good business. Indeed, it might make more sense to beam power from Earth to space stations, if they needed it.

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What are the extra costs? Broadly, they fall into the following categories: Transmission losses, thermal losses, logistics costs, and space technology penalty. Individually, any one of these issues cancels out the benefits, and combined they leave space-based solar power at least three orders of magnitude more expensive than the terrestrial equivalents.

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For a baseline comparison, consider a GW-scale power station. For terrestrial solar, this consists of standard panels on single axis mounts, covering about 10 square miles. For the space-based solar case, an identical area of land is covered instead with an antenna, a mesh of conductive wire held above the ground, to absorb the transmitted microwaves and convert them to electricity. An identical area implies similar overall energy fluxes, which is correct.

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Transmission losses: The process of converting sunlight to electricity is about 20% efficient, depending on the type of panel – and this is a loss common to both systems. In addition, the space-based system has to convert the electrical power back into EM radiation, which is converted back into power on Earth. Proponents think that it should be possible to perform each conversion with 90% efficiency, but even beam-forming that well is not possible without a much larger antenna. My personal opinion is that the end-to-end microwave link efficiency would be lucky to exceed 40% efficiency, which erodes the competitive advantage substantially.

Thermal losses: The conversion efficiency of the high-power microwave transmitter has a nasty side-effect, namely that what isn’t transmitted is wasted as heat, and that heat has to go somewhere. If the transmitter is 80% efficient (which is being very generous), then it will have to radiate 200MW of thermal power. This is a different problem to the thermal losses in the solar panels, which are more like 4GW but spread over a huge area that is in radiative thermal equilibrium with its environment. Instead, the microwave power electronics will need a huge cooling system. If the electronics can operate at 350K, then the radiator power will be 850W/m^2, so the radiator will need a total area of 23ha, comparable to the total size of the solar array and the microwave transmission antenna. In contrast to the usual claims of perfect scaling efficiency with solar arrays in microgravity, a large space-based solar power system will also need a huge antenna and cooling system, which don’t scale quite as nicely.

Logistics costs: Consider transportation cost. Today, SpaceX has crushed the orbital transport market with a price of around $2000/kg. Compare this to the worldwide network of intermodal containers, which can transport anything in 20T units almost anywhere on Earth for about $0.05/kg. Even if all of Elon Musk’s wildest Starship dreams come true, transport costs will dominate the total capex of any space-based solar system, by many orders of magnitude. A factor of 10x improvement in resource does not make up for transport costs which are more than 10,000x higher. If logistics costs are more than 0.1% of current solar farm costs (they’re more like 20%), then increased transport costs completely negate the improved solar resource. It’s not even close.

One further aspect of logistics bears closer examination. In our baseline case, we considered an array of panels strung up on posts, compared to a mesh of wire strung up on posts. It turns out that (as of 2019) a substantial fraction of the overall cost of a solar PV station is the mounting hardware, which is also required by the microwave receiver. So if the mounting hardware costs 20% of the overall deployment cost for terrestrial solar, that places a strong upper bound on total system cost allowable for space-based. In other words, does anyone seriously believe that the microwave receiving antenna could cost 20% of the overall system capex, the other 80% to be used to launch thousands of tonnes of high performance gear into space? Put another way, the most cost-effective way to get a GW of power out of a microwave receiving antenna is obviously to tear down the wire mesh and sling up a bunch of solar panels, which can be ordered with a lead time of weeks from any of dozens of suppliers worldwide with widely available financing.

Finally, the space technology penalty. On Earth, we are living in an extremely exciting time for energy. Hundreds of major companies are competing on development cycles measuring only months to provide solar panels in an industry that’s growing at 20% a year. As a result, costs have fallen by 10% a year, and in the last few years, solar and batteries have neared, equaled, then utterly crushed all other forms of electricity generation. Initially, this process occurred on remote islands with high fuel import costs. Then the sunnier parts of the US. The rampage continues northwards at about 200 miles a year. The industry can sustain 30% deployment growth rate worldwide for another decade at least, before saturation occurs.

Today, I can pick up the phone and any of dozens of contractors in the LA market can fill hundreds of acres with panels, each built to survive 30 years under the harsh sun and sized perfectly for deployment using the latest tech, which is men in orange vests with forklifts.

In contrast, space technology has not benefited from such breakneck levels of growth, demand, and investment. Prohibitive maintenance costs demand perfect performance, and low rates of deployment ensure a slow innovation feedback loop. The result is that none of the current incredibly cheap solar panels could work in space, where thermal and vacuum, not to mention stresses of launch, would destroy their operation in days.

Instead, space operators rely on more traditional supply chains, with the result that building anything for space takes years and costs billions. Right now, a billion dollars invested will buy about 100MW of solar panels on the Earth, or 100kW of solar panels in space. This is a factor of 1000, and it also erases the advantages of more sunlight in space.

These four elements, transmission, thermal, logistics, and space technology, inflate the relative cost of space-based solar power to the point where it simply cannot compete with terrestrial solar. It’s not a matter of 5% here or there. It’s literally thousands of times more expensive. It’s not a thing.

Tunnels are a staple of both science fiction and popular journalism regarding human habitations on the Moon, Mars, or other rocky places, Casey Handmer notes:

They’re fun to write about and interesting to put on screen. I’ve lost count of the times I’ve seen beautifully illustrated Mars city maps featuring a hexagonal grid of domes connected by tunnels. On a visual level, it certainly ticks all the right boxes.

And yet, while I’ve wasted years of my life on real estate websites I’ve never seen a subterranean house on the market. They do exist, if you want a converted ICBM bunker or limestone cave, but they’re a definite rarity.

Why?

The simplest explanation is that digging holes, particularly really deep ones, is very energetically intensive and expensive. The cost of building a road tunnel works out to be about $100,000 per meter, or equivalent to a stack of Hamiltons of the same length! For comparison, $100,000 will buy materials and labor on a respectable manufactured home, or substantial renovations.

Indeed, on Earth, underground construction is basically unknown except for nuclear bunkers. These have two powerful reasons to accept the cost and inconvenience: unlimited sweet DoD money, and surviving really big explosions.

Why build underground in space? The usual explanation is to provide shielding against galactic cosmic rays, or micrometeorites.

It is true that tunnels deep underground are relatively safe from both, and also well thermally insulated. But as I discussed in the blog on space radiation, relatively little shielding is necessary even in areas that people spend a lot of time, such as sleeping areas. And even if that works out to be a meter or two of rock, it’s orders of magnitude less effort to drop sandbags on the roof of some structure constructed on the surface, than to dig a hole of the necessary size deep underground.

Micrometeorites are not a concern on Mars, which has a thin atmosphere, and can be well shielded on the Moon with a thin blanket of loose rubble.

If there’s a central point to my blogs on space architecture, it’s that our cities and houses on Mars will look and feel a lot more like regular houses on Earth, and for the same reasons. It may not be very exciting, but the most important consideration for design and construction, on Earth or in space, is expedience. Given the relative scarcity of human labor in space cities, structures will have to maximize usable area and minimize effort even more than on Earth. Instead of tunnels, think warehouses and aircraft hangars! At least they can have natural light.

Casey Handmer trusts that the Zeppelin engineers knew what they were doing:

But they were built of primitive 2000 series aluminium alloys, doped canvas, and cow gut. I think we can improve on the materials. In particular, carbon fiber pultrusions are about six times as strong and far simpler to assemble than the typical recursive riveted Zeppelin truss.

These beams could be integrated with injection molded nodes and tensioned with Kevlar cables. Gas bags would be aluminized mylar (space blanket) while the outer cover could be ripstop Nylon. (It is hard to overstate just how much better Nylon is than what came before. Try skydiving with a hemp parachute!)

Alternatively, one could optimize for cost instead of performance and cobble together a functional structure from foam core fiberglass produced onsite with simple tooling and assembled like LEGO by hand in the open air.

Alternatively, use a welded aluminium truss segment like the ones used for events. There are about half a dozen manufacturers just in Los Angeles, and while some tooling changes would be needed to support a thinner tube wall, the Hindenburg needs about 20 km of truss.

The exciting thing about the low cost approach is that it closely mirrors the approach of the original Zeppelin designers, who were severely resource constrained. Indeed, with modern materials I think it could be possible to home-build a Zeppelin at a similar scale to the Bodensee for less than $100k and with less than ten person-years of labor. This brings it into the realm of home built yachts and kit aircraft.

Such a home built would have to use innovative manufacturing to be assembled outside a large hangar, perhaps by extruding it tail first from the ground. It may also exploit a more conventional power system with salvaged automotive engines turning propellers in pods. The lifting gas of choice would be hydrogen, in order to keep operating costs low. Provided the space between gas bags and cover is sufficiently well ventilated that hydrogen can never build up at a concentration between 4% and 75%, ignition and/or deflagration is unlikely without a major structural failure or gas bag tear.

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The structure, at 118 T, is just over half the total lift of 216 T. Doubling structural margins with composites could still reduce overall structural mass by a factor of 3, to 39 T, while also greatly simplifying assembly. That’s less than the weight of a railway carriage! All else being equal, the payload increases from 9.5 T to 88 T, almost a 10x improvement. Payload fraction increases from 4.4% to 40%.

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The Hindenburg had 59 T of fuel and 4 T of oil. Operating with relatively primitive and heavy diesel engines, it could cruise at about 80 mph, crossing the Atlantic in 2.5 days. As it burned fuel it either had to vent hydrogen or capture rain to offset the reduced mass. The earlier Graf Zeppelin used neutrally buoyant blaugas, enabling longer flights over the equator to Brazil since burning didn’t change the weight of the airship.

But there’s no rule saying we have to afford the Zeppelin designers the benefit of copying their propulsion system. Like materials, we can assume that if they had something better, they would have used it.

My suggestion is to affix a steerable electric fan to each structural node. These ~1700 small motors would be able to completely control the boundary layer flow over the airship, stabilizing it in gusty wind and enabling fine-grained control while maneuvering. No need for a big, heavy and structurally vulnerable tail. Many airships were damaged or lost due to gusts while attempting to dock or enter a hangar. No more!

Each motor would be powered during the day by thin film solar panels built into the airship’s skin. This should be able to drive it along at about 50 mph. This number is quite robust to scaling as both drag and power increase as linear dimension squared, while elongating the airship to reduce frontal area both increases structural difficulty and doesn’t actually improve drag.

For additional power or during the night, a neutrally buoyant mix of propane and ethane can be burned in a compact turbine generator. In such a case, range is limited only by what fraction of the envelope is devoted to fuel as opposed to lifting gas. Powering cruise at 50 mph for 7 days would require 33 T of gas, which would consume about 15% of the displacement volume. This increases as the cube of speed.

The original Zeppelins never made money, he notes, and modern airships probably wouldn’t, either:

Despite hopes, they are not particularly useful for hauling cargo to remote areas. Airships depend on finessed trim and buoyancy — so dropping or picking up a huge cargo load somewhere is a big ask. They’re also not much use near the ground in wind, and no better than alternative logistics methods for delivering containers anywhere.

The team at Terraform Industries is now 11 people, Casey Handmer says, working towards a near-term future where atmospheric CO2 becomes the preferred default source of industrial carbon:

Our process works by using solar power to split water into hydrogen and oxygen, concentrating CO2 from the atmosphere, then combining CO2 and hydrogen to form natural gas. Very similar processes can produce other hydrocarbon fractions, including liquid fuels. Synthetic hydrocarbons are drop in replacements for existing oil and gas wells and are distributed through existing pipeline infrastructure. As far as any of the market participants are concerned, fuel synthesis plants are less polluting, cheaper gas wells that convert capital investment into steady flows of fuel in a boringly predictable way.

Most recently, Terraform Industries succeeded in producing methane from hydrogen and CO2.

There is nothing particularly special about the technological approach we’re taking. Each of the various parts is built on at least 100 years of industrial development, but up until this point no-one has considered scaling these up as a fundamental source of hydrocarbons, because doing so would be cost prohibitive. Why? The machinery is not particularly complex, but the energy demands are astronomical.

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The solar panel industry has been growing by about 25-35% per year for the last decade, making steady progress on cost and becoming a mainstream energy source to the point where its continued displacement of other grid power sources is partly limited only by the battery manufacturing ramp rate, itself redlining at about 250%/year!

Wright’s Law describes the tendency of some products to get cheaper with a growing manufacturing rate. It is not guaranteed by the laws of physics, but rather describes the outcome of a positive feedback loop, where a lower cost increases demand, increases revenue, increases investment, increases cognitive effort, and further lowers cost. For solar technology, the same effect is known as Swanson’s Law, and works out at 20% cost reduction per doubling of cumulative installations since 1976.

This is not the full story, though. Solar has only been cost competitive with other forms of grid electricity generation since about 2011, at which point investment and engineering effort greatly increased. Since 2011 there has been an acceleration of production growth rate and an increase in the learning rate, such that the cost decline is now 30-40% per doubling. For more details, check out Ramez Naam’s excellent blog on the topic.

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In particular, the US consumes about 37 Quads of energy for electricity generation, of which about a third goes into wires and the rest is lost in thermodynamic heat loss in generating stations and transmission. Ceteris paribus while solar PV and batteries are much less inefficient, PV capacity factors are limited by daytime sunlight, seasonal daylight variations, poor weather, and mismatches between times of peak generation and consumption. The end state of the solar electricity build out will likely see 3-6x overbuild in nameplate capacity, and large variations in electricity price by time of year, day, and location. These price differences, incidentally, already drive the engine of arbitrage which has turbocharged the battery industry.

Analysts recognize that coal and natural gas used for electricity production will eventually be displaced by renewable generation. Just as converting chemical energy in the form of fuel into electricity endures 45-75% thermodynamic losses, converting electricity back into chemical fuels loses 60-70% of the energy in the process. Converting solar power into natural gas only to burn it in a gas turbine power plant could help with long term seasonal energy storage but is so much less cost competitive than other ways to stabilize electricity supply that we should expect this usage modality in, at most, niche cases.

But what of other uses of carbon-based fuels? In the US, roughly twice as much energy is consumed by transportation, industry, and other uses, as in direct electrical generation. Electrification of cars and trucks proceeds apace but other, more fuel hungry forms of transport including aviation are harder to convert. Fuel uses for high temperature industry will continue to demand non-electrical processes. In particular, it’s easy for industry to transition to purely electrical energy if it’s cheaper for them to use it, but not if it’s not.

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13 Quads of electrical consumption in the US will require perhaps 50 Quads of solar generation, profitable deployment of batteries, and no further miracles as displacement occurs organically over the next 10-20 years. 70 Quads of fossil fuel consumption will be displaced by about 240 Quads of solar generation, and there will be a steep price incentive to enable this displacement.

In the US, we are anticipating a 6-10x demand increase once solar costs cross the critical threshold.

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What is the solar cost threshold of interest? One barrel of oil contains about 1.7 MWh of chemical energy. Synthesizing a barrel of oil requires about 5.7 MWh of electricity at 30% conversion efficiency. Crude oil prices are between $60 and $100/barrel, indicating cost parity at between $10 and $17/MWh. There are already solar farms installed in some places that sell power at these prices, and between now and 2030 solar costs should come down at least another 60%

Electric aircraft have certain advantages and disadvantages, Casey Handmer notes:

Advantages include mechanical simplicity and reliability, reduced noise, reduced cost, increased efficiency, and reduced engine weight. The major disadvantage is that battery energy density is still, at best, about 50 times less than gasoline. Even factoring in other efficiency gains, electric aircraft have greatly reduced flying time and range.

The underlying reason that I believe electric aircraft can break the sound barrier is that electric motors can deliver far higher power-to-weight ratios than piston engines, jets, or turbines. The F-4 Phantom is a textbook example of high thrust, being able to (just) achieve a vertical climb. In contrast, for $100 I can buy a racing drone that can accelerate vertically at 10 gs. There are other factors at play but a power-to-weight ratio of 10 screams possibility.

In terms of fundamental physical limits, let’s consider the Concorde. While most fighter jets can fly supersonic for at most a few minutes, the Concorde couldn’t do in-flight refueling and had to cross the Atlantic in a single hop. It could cruise at Mach 2 for 201 minutes! Let’s say that when battery energy density and electric motor efficiency are factored in, electric systems with present technology would have 10x less range. Still, an electric Concorde could fly for 20 minutes, covering almost 450 miles. That’s more range than a Tesla!

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Of course it should be possible to develop a better configuration than a Concorde clone, but it’s an interesting starting point. In particular, many supersonic aircraft use delta wings because of relatively consistent lift characteristics over a range of speeds. It’s not that Concorde needs that enormous wing to fly at Mach 2 at 60,000 feet. Concorde needs the huge, draggy wing to fly slowly enough to land on a runway. But electric aircraft can deliver the necessary power and control to take off and land vertically (VTOL) like a helicopter, obviating the need for much wing at all.

Before diving into the specifics of different subsystems, I will motivate an example point design by appealing to the obvious. A supersonic electric aircraft must have a lot of thrust and minimal drag. When we think about what it might look like, the F-104 Starfighter comes to mind. Long, pointy, and with the barest minimum of a wing.

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Ordinarily, fast planes use jet engines for propulsion. Their compressor stages operate at subsonic speed so all supersonic jets have complex intake systems designed to decelerate inrushing air with a series of shocks prior to impacting the turbine. Building a turbine to ingest a supersonic stream ordinarily seems like a recipe for disaster. Jets need subsonic flow because combustion typically occurs subsonically. Electric propellers have no such constraint, and nor do they care that 80% of the atmosphere isn’t oxygen.