Sunday, August 5, 2018

Atmospheres and Terraforming


I have been meaning to write a blog about terraforming for many years, but the recent controversy (thanks Elon) about some exciting MAVEN results is the perfect opportunity.


MAVEN, or Mars Atmosphere and Volatile EvolutioN, is a satellite orbiting Mars since 2014 specifically to study its atmosphere. Previous Mars missions have studied parts of its surface, and the InSight mission due to land in late November will study, for the first time, the interior of the Red Planet.


Mars' geological history is an enduring mystery. Much of the surface is heavily cratered, like our moon, meaning that we have a pretty good record of what ancient rocks were doing, because they're still there. In contrast, Earth's surface has been worn down and subducted many times through the process of plate tectonics. Yet if we look closely, there are clear signs of flowing and standing water. This is puzzling in many ways. Where did the water come from? Where did it go? Why did it stop flowing? And, given that back when this surface formed the sun was much younger and cooler, how could Mars have been warm enough to sustain liquid water on its surface?


This image shows gullies and deltas in the south west part of Gale Crater, not far from where the Curiosity rover is currently driving.


MAVEN was designed to study the evolution of Mars' atmosphere, and a series of results have provided exciting new insights. It has long been theorized that Mars' atmosphere was gradually stripped away by the solar wind. Unlike Earth, Mars lacks a strong gravity well and a big magnetic field, which increases the rate that gases, particularly lighter gases, are stripped from the planet. This accounts for why Mars' atmosphere is today both thin and mostly of CO2. But since gases are constantly bubbling up from the interior of the planet through volcanoes, we needed to get quantitative data. MAVEN provided that data. Today, Mars loses about 100g/s, or 3000T/year, of atmosphere. This sounds like a lot, but the total mass of Earth's atmosphere, for comparison, is 5*10^15T. To put 3000T/year into perspective, a large passenger jet produces about that much CO2 in a week.


It is a popular misconception that for humans to live on Mars, Mars would need a magnetic field. There are all kinds of difficult things about living on Mars (see http://www.caseyhandmer.com/home/mars) but building a planetary scale magnetic field would be at another level entirely. Fortunately, Mars does not need humans to built it an artificial magnetic field for any reason! As we will soon see, atmospheric loss rates are vanishingly tiny over the relevant time scales of less than a billion years, and Mars' current atmosphere provides adequate, if not flawless, protection against space radiation for nearly all cases.


So what's all the fuss about?


Noted Mars human exploration advocate Robert Zubrin, together with planetary scientist Chris McKay, wrote a series of papers in the early 1990s exploring the idea of terraforming Mars (see eg. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.24.8928&rep=rep1&type=pdf). Taking Mars Viking data and using rather primitive simulations, they were able to show that, under some reasonable assumptions, there was enough CO2 frozen into the surface of Mars that only a tiny addition of heat, by humans, would be enough to tip the climate away from its current frozen state to a runaway greenhouse. As the planet warmed, it would release more gases, warming further! Eventually, this process would be slowed by the lack of remaining accessible gases. If the atmosphere became warm enough, water would melt and restart the hydrological cycle, creating a much more Earth-like environment, albeit with a poisonous atmosphere of mostly CO2. Still, having to wear an oxygen mask to breath is much less onerous than an entire space suit.

Potential problems included uncertainties about the stability of a hydrological cycle on a planet with such tall mountains, as water would snow there and accumulate in glaciers, removing liquid water from the system and reflecting more of the sun's heat into space. Additionally, the total reserves of CO2 in the polar caps and under the soil was poorly constrained.


Last week, a Nature paper (https://www.nature.com/articles/s41550-018-0529-6) was published by Jakosky and Edwards arguing that, based on data from more recent orbiters, the total near-surface reserves of CO2 are much too low to built up the atmosphere enough for terraforming. What a bummer!


I'm not sure if I find this result surprising. I would think that if Mars were, according to Zubrin and McKay, only a few degrees away from runaway warming, that a sufficiently large meteorite impact or volcanic eruption in the last few million years might have been enough to tip the scales. And perhaps, in the past, it was. There is some evidence for smaller scale water flows in the more recent past, but whatever happened and when, the planet is cold and dry now. According to the principle that our present time is not "special" in any way, that suggests that Mars reasonably robustly and quickly returns to something like its present state. How much meddling is necessary to terraform the planet is another question entirely!


Of course, the usual players got into the act on Twitter: https://twitter.com/DiscoverMag/status/1024135166007095296.

Ah Twitter, where you can watch your heroes disgrace themselves in real time!


Clearly the only way to fix this impasse is for me to write a blog no-one will read adding almost no substantive information to the deafening screams. But with math!


The Earth's atmosphere is thickest at the surface, and gets thinner as one ascends until it peters out into space. At the surface, we experience air pressure of 101.3kPa, or 1bar. I prefer bar as a unit of measure in this case!


Even though gas is roughly 1000x less dense than condensed matter, it is still affected by gravity. Indeed, the reason that the air is thicker and at higher pressure down low is that all the air above it is pressing down on it. So even if we somehow liquefied all the air (by making the Earth really cold) the pressure at sea level would stay the same. In other words, a phase change doesn't change gravity! Only now the Earth would be covered not by a gaseous atmosphere, but by a thin ocean of mostly liquid nitrogen and oxygen.


I personally really like this way of thinking about global gas and liquid resources. That is, in terms of a global equivalent liquid layer of some depth.


Let's start with our home planet, Earth. We're going to ignore sources of volatile molecules beneath the crust, though there's a huge amount there too, and focus on surface resources. Earth's global equivalent depth of water is 2.6km. The next most abundant molecule is nitrogen, with a global equivalent layer depth of 8m. Then oxygen, with 2m. 10cm argon, 4cm water, 4mm carbon dioxide (up from 2.5mm 5000 years ago), 0.2mm neon, and a hair of helium, methane, krypton, and hydrogen. This is a total depth of 10m, which will be familiar to SCUBA divers computing pressure at depth.


By comparison, Venus has an atmosphere that, if liquefied, would be more than 600m deep.


For humans to breathe, they need an atmosphere with oxygen, some buffer gases, and not too much of poisonous gases, such as CO2 and CO, among many many others. But how much oxygen do humans need? The partial pressure of oxygen in haemoglobin, the blood's oxygen carrying molecule, is 130mbar. This means that at a partial pressure of oxygen below this, the blood is not saturated with oxygen, and less physical activity is possible. For healthy, adapted, young people it's possible to walk around and live at 5500m of altitude (ppO2 = 100mbar), but it's pretty hard to reproduce over 4000m (ppO2 = 128mbar).


There are various tricks people use to exist higher up, such as breathing pure oxygen with positive pressure, but the same general rules apply. Lots of mountain climbers with great gear die all the time. Ideally, an atmosphere with 0.2bar is enough to allow physically active humans to breathe from an unsealed oxygen mask, but without a pressure suit. At the absolute lower limit, the Armstrong Limit of 68mbar is the vapor pressure of water at human body temperature (https://en.wikipedia.org/wiki/Armstrong_limit). Below this, the body's surface fluids boil and adequate oxygen cannot be delivered by any means without a pressurized garment.


On Earth, 0.2 bar is achieved with a depth of 2m of liquid water or liquids of similar density. On Mars, the gravity is 37% as strong, so a 2.7x greater depth of liquified gas is required. Condensed CO2 is about 1.5x as dense as liquid water, so taking these numbers into account, a layer of dry ice 3-4m thick on Mars is adequate to produce an atmosphere with oxygen mask enabling pressure. Is there 4m of CO2 mixed into Mars dirt within 200m of the surface?


The next step is to examine the known resources on Mars. Mars' atmosphere is so thin it's about 1/100th as thick as Earth's. That is, if it were condensed, it would be about 10cm thick on the surface. In terms of its composition, that tiny crust is 9.6cm CO2 (+- 2cm seasonally, as some freezes out in winter), 2mm argon, 2mm nitrogen, 0.15mm oxygen, and less than a hair of carbon monoxide.


Despite the fact that Mars' atmosphere is almost totally CO2, it is thought that Mars' volcanic processes have produced significantly less CO2 over geological history than Earth, because Mars' small size and resulting reduced pressure in the mantle is unable to produce much CO2 from various metamorphic transitions at depth.


So ideally a runaway greenhouse terraforming first effort on Mars would increase the volatilized supply of CO2 from its current level of about 10cm global equivalent depth to 4m, an increase factor of 40.


At this point I would like to point out why it is that losses due to solar wind don't matter. If 4m of CO2 is produced in, say, 100 years, then that's a rate of 4cm/year. Even if global losses increased from 3000T to 300,000T/year due to an increase in cross section, the annual loss rate is an equivalent depth of 2nm. It's in the noise.


Zubrin and McKay (1993) attempted to estimate reserves of CO2 available. The two main sources they considered were the south polar cap and frozen into the regolith, with 100mbar and 400mbar of CO2 respectively. This is equivalent to 1.8m and 7.2m global equivalent depth respectively, or easily enough to get to a warm, wet, oxygen-mask requiring atmosphere, even if only half the CO2 was readily accessible.


25 years later, we know a lot more about Mars, so let's check how Jakosky and Edwards have refined these early estimates. They estimate a total resource of 10cm of CO2 at the south pole (which turned out to be mainly water ice), and 1.8m absorbed on minerals in the regolith. They also provide an upper limit on total CO2 in clathrates (150mbar, 2.7m) and near-surface carbonate rocks (150mbar, 2.7m), despite admitting that there is little evidence for either, especially anywhere near that much of them! In total, there doesn't seem to be enough CO2 remaining on Mars to warm the atmosphere.


In response, Robert Zubrin tweeted:

Both Zubrin and Jakosky estimate 1% soil mass fraction of absorbed CO2 by weight, though Zubrin goes down to 200m instead of 100m. Reducing his estimate to 100m, 150mbar of atmosphere is still a lot more than Jakosky's estimate of 40mbar. What's going on here?


I don't know for sure how they did their math, but it seems that Jakosky has assumed a regolith density equivalent to water, whereas rock is typically 3x as dense as water. Zubrin's estimate would call for a global equivalent layer of 4m of CO2 in 200m of regolith, since condensed CO2 is about 2x less dense than rock. 4m of CO2 under Mars' gravity produces a pressure of 220mbar, which while 25% less than Zubrin's estimate, would be adequate to walk around in.


That said, 1% w/w is as much of a guess as 200m effective absorption depth. Even on Earth we don't have a good understanding of the water fraction of permafrost, or its thermal conductivity, or extent, and permafrost is a reasonably good analog for Mars perma-CO2-frost.


As far as I can tell, there just might be enough CO2 on Mars to begin a greenhouse warming effect, but even in Zubrin and McKay, they recognize that uncertainties in regolith affinity for desorbed CO2 could shift their equilibrium a lot. In other words, it really doesn't hurt to tip the scales solidly in the desired direction. We know this is possible, since with a 1mm addition of CO2 to Earth's atmosphere we've warmed the planet considerably!


A wide variety of terraforming methods have been proposed over the years, some less practical than others. The overarching goal is to increase the total amount of heat energy on the planet. The baseline heat source is the sun, which delivers about 10^16W (10 petawatts!) to the surface of Mars.


In order from least sensible to most sensible:


Nuking the poles. The Earth has about 15,000 warheads with a total yield of 6500MT of TNT, which is 2.7x10^19J. This sounds like a lot, but is equivalent to only 45 minutes of sunlight. Even if the bombs were carefully landed and detonated under the ice caps, instead of exploded while flying by, the net contribution to the heat budget is negligible. Even if all the uranium in the crust of Earth AND Mars were enriched and allowed to produce heat in reactors, it wouldn't be enough to make a difference. The sun is THAT powerful, which is why solar energy is so exciting.


Crashing comets. Mars is pretty dry, though the exact quantities of water left frozen under the surface is not very well constrained. It could be between 20cm and 200m global equivalent layer. Even if it turns out there's no water or gas left, the thinking goes, comets or small moons could be brought in from the outer solar system and crashed into the planet to thicken the atmosphere and warm things up a bit. Unfortunately, the sheer quantity required to do this exceeds known reserves of comets! Not to mention the fact that landing enough of them to make a difference would completely resurface the entire planet and kick up enough dust to ruin things for centuries. Finally, the energy and time required to move icy bodies from the outer solar system inward is quite prohibitive, compared to the requirements of other methods listed below.


Giant mirrors. The fundamental advantage of mirrors is that they can be made extremely thin, and thus with relatively small quantities of material. Additionally, a mirror can be made in a curve to concentrate sunlight on a particular area, which is necessary to either melt down to subsurface resources or vaporize carbonate rocks. A series of mirrors 100km on a side could be made with as little as 40T of material, so in principle launchable on a Falcon Heavy then flown using solar wind pressure to Mars, before finding a stable equilibrium between Mars gravity and solar pressure, from where to gently barbecue the planet.


The last two options are concerned less with adding more heat to mars, but preventing heat from escaping once it arrives. They require interventions on the surface.


Black dirt or lichen. The amount of light reflected by an object in space is the albedo, and varies between 0 (perfectly black) and 1 (perfectly reflective). Mars' albedo is 0.15, meaning that 85% of the sun's visible light that falls on it is absorbed. If we could decrease the albedo a bit more, the planet will absorb more heat energy from the sun, and warm up. Mars' albedo increases during the southern winter, as a thin layer of CO2 freezes out of the atmosphere, covering large areas with reflective white snow. The best way to reduce this effect is to blacken the snow, such as occurs in the ski fields of Europe after an Icelandic eruption. Mars is already quite dusty, but the distribution of black dust over the surface would increase the absorption of solar energy. Even better, dark colored lichen, genetically engineered to survive on the harsh surface, would propagate itself over the planet "for free", without humans having to go out and paint 145 million square km of landscape.


Greenhouse gases. As far as CO2 goes, it's a pretty good greenhouse gas, blocking emitted thermal radiation across a wide range of wavelengths. It does, however, have some holes where it is transparent and allows heat to escape through the atmosphere and back into space. This blog (https://wattsupwiththat.com/2011/03/10/visualizing-the-greenhouse-effect-emission-spectra/) has a great explainer on the matter, while (Wordsworth et al. 2017 https://arxiv.org/pdf/1610.09697.pdf) discusses the implications for the early Mars climate.


Human-produced greenhouse gases can be selected to block the gaps in the CO2 absorption spectrum. The best gases for this purpose are perfluorocarbons, or PFCs. On Earth they're generally used in relatively small quantities in chip manufacture, medicine, and the production of Teflon. But on Mars, provided adequate supplies of fluorite mineral from which to derive fluorine were located, rock-eating PFC factories would dump gases like CF4, C2F6, and C3F8 into the atmosphere as fast as they could be built.


(Marinova et al. 2005 https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2004JE002306) estimates that the addition of 0.2Pa of the best gas mixture is adequate to trigger runaway warming. 0.2Pa is a global equivalent layer of 6.6 microns, but since they'd have to be produced at discrete locations, a consideration of the total mass required is in order. 0.2Pa is equivalent to a total production of 7.8x10^9kg, or 0.958km^3 (in the condensed state), of which about 80% would be extracted from fluorite, and 20% from CO2 in the air. This sounds like a lot, but in 2017 we managed to extract 5.4km^3 of oil from the Earth. If fluorite were discovered in dry lake beds at 10% ore concentration, then an area only 10km x 10km x 100m would need to be excavated, comparable to the largest open cut mines in the world today. Of course, this process would occur not at one huge hole but numerous sites selected for natural resource abundance, and over many decades.


Production would, of course, require massive automated digging machines powered by nuclear power plants, but the net heat retention for the planet per joule of uranium used would be millions of times greater than detonating it in an atomic bomb. Once PFC levels were high enough, runaway warming using frozen CO2 would be triggered, eventually resulting in a warm, wet, though poisonous atmosphere.


Finally, let's examine long term prospects for Mars. Using variants of the above processes, Mars could likely be given a warm, wet atmosphere in a small number of centuries. But even if humans can walk around outside wearing only an oxygen mask, it's not quite terraforming if plants and animals can't easily exist. To do this, a large fraction of the CO2 atmosphere will need to be converted to oxygen. For humans, a global equivalent layer of about 3m of oxygen is needed. This is more oxygen, on a per area basis, than Earth's atmosphere, because of Mars' lower gravity. If Mars' atmosphere has stabilized with, say, only 6m equivalent depth of CO2, converting half of this to oxygen will severely damage the planet's greenhouse. More worrying, most plants and animals cannot tolerate high levels of CO2, no matter how much oxygen is available.


In the Mars Trilogy, author Kim Stanley Robinson elides this difficulty by proposing that organisms on Mars wear a CO2 filter mask, or get a genetic modification to increase their CO2 tolerance, as some diving animals like crocodiles can on Earth. Such a future is so far away at this point that I can offer little better than science fiction myself! Perhaps ongoing production of PFCs, plus orbital mirror blasting of carbonate and nitrate rocks will produce enough atmosphere that an Earthlike existence will be possible. In any case, careful ongoing and energy intensive management will be necessary to restabilize the climate at any desired level.


I feel like it's time to wrap up. I think it's very exciting that our ongoing robotic missions to Mars have enabled such an interesting conversation, and that powerful dreams for the future continue to inspire hope in new generations. Sending humans to Mars is within our technological capabilities. Sustaining them on the surface indefinitely is possible. And, eventually, making Mars more like Earth is a worthy challenge.



Saturday, July 21, 2018

The High Frontier: A Technical Critique

The High Frontier: A Technical Critique
Casey Handmer

"The High Frontier," published in 1976 by physicist Gerard O'Neill, remains the text on space industrialization. The culmination of a series of studies through the early 1970s, it presents a compelling vision for life for millions of people beyond the Earth. Today, in 2018, its themes continue to resonate. As several space companies position themselves to launch humans into space on a permanent, sustainable basis, I decided to write a technical critique of "The High Frontier." What works, what doesn't, and how will companies using it as a blueprint, including Blue Origin, have to adapt its ideas after 42 years of intervening discovery?

In this critique, I will:
  • Begin by restating O'Neill's arguments in the strongest possible light.
  • Examine the assumptions that underlie his quantitative estimates.
  • Identify any misperceptions in need of correction.
  • Establish feasibility bounds and figures of merit, in comparison to the original assumptions.
  • Explore ways in which the vision could be extended with a more modern perspective.

What is the High Frontier?
O'Neill paints a compelling image of gigantic cities in space. Consisting of large pressure vessels capable of housing thousands to millions of people, they would rotate to provide artificial gravity. Separate sections would be used for industry or high intensity agriculture with 24 hour sunlight, enriched CO2, and precision hydroponics. The living sections could be landscaped in any desired style - O'Neill is a particular fan of Tuscan architecture. Thus protected from the vacuum of space, people could conduct routine commerce and industry of practically any sort, freed from the constraints of Earth's gravity, limited resources and available space.


In 1976, Earth's resources seemed more pressed than ever. With population growth since 1945 averaging 2% per year, and energy consumption 7% per year, it seemed quite likely that by the early 2000s, Earth would be consumed by the throes of a Malthusian catastrophe. Expansion of industry to space, with its substantial resources, was a relatively cheap alternative. Not long after the book was published, growth stabilized at a more sustainable pace, and in the last few years energy and economic growth seems to have begun to decouple from hydrocarbon extraction, potentially freeing humanity of a major energy constraint.


A gigantic rotating space city would weigh millions of tonnes and could not possibly be launched in one piece, or even in sections from Earth. Once in space, it would continue to require a variety of raw materials to make up for gradual entropic losses, and a versatile, vibrant industry to process raw materials into any of the thousands of products needed to keep this island in the sky functioning.

While launching supplies from the Earth is possible, there are other sources of bulk raw materials in space with much less gravitational binding energy, including the Moon and asteroids. O'Neill envisioned an electromagnetic mass driver system that could launch small slugs of partially processed moon rock from a series of mines on the Moon, to the city somewhere nearby. He and his students even built a series of mass drivers to demonstrate the technology, which is today considered reasonably mature. Extremely high accelerations over short distances reduce the amount of infrastructure needed, while a stream of 1kg packets fired every second or so is adequate to provide a city with enough raw materials to make up for loss and use. Today, we know of numerous low energy transfer orbits which could convey material from the moon to almost anywhere in cis-Lunar space.

With industrial self-sufficiency sketched out, O'Neill turns to the question of economic self-sufficiency. Building and operating a space city would be enormously expensive, and would continue to require shipments of specialty components, such as computers, from Earth, essentially forever. What, then, could the space city offer Earth in order to complete the trade? While the city has a supply of moon rocks, O'Neill recognized that there wasn't concentrations of sufficiently valuable minerals on the Moon to make it worthwhile for selling in an Earth-based market. The city in space had become a solution looking for a problem.

O'Neill settled upon space solar power as the source of space-derived value necessary to balance the trade. Space solar power has certain advantages: The product could be beamed to Earth without having to go through the trouble of re-entry. The product was available essentially 24 hours a day, while on Earth the sun sets at night. Recall that in 1976, energy storage technologies such as batteries were barely on the horizon.

In addition, with 7% per year growth in energy demand, the US and every other country was looking at major infrastructure investments to meet demand for the foreseeable future. The entire grid would have had to have been overhauled every few years, at significant expense.

The final part of the problem that O'Neill examined was bootstrapping. What was the minimum viable space city that would have to be launched from Earth, could support enough people to build most of its structure from Lunar material in space, and then grow from there? Over a series of studies, O'Neill and his team were able to reduce the size of the minimal investment to only 250 shuttle launches, or 6500 tonnes. In 1976, the shuttle had not yet flown and 250 launches was thought to be about five years worth of flights, which seemed quite reasonable even without expected follow-on improvements in launch technology.

Quantification of assumptions
Thus far, O'Neill has sketched a compelling vision, a future for humans in space, unfettered by the limitations of Earth. At no point does settling the High Frontier require any miracles of technology, warp drive, or an investment equivalent to the entire GDP of the Earth for 100 years.

That said, there are still a number of assumptions, all of which need to be true, for O'Neill's vision to be viable. The most crucial of these center around the economic question.
  • Space power needs to be lucrative.
  • Space launch needs to be cheap.
  • Space industry needs to be compact.
  • Overall, the space cost multiplier needs to be low.

I will begin with the space cost multiplier question, since it's the highest level estimate possible in this case. In 2018, the per-person-day-in-space cost of the space program is about $4m. The per-person-day-on-earth cost for people of equivalent qualifications is about $400, so the human space operations cost factor is about 10,000. It is not necessary, or particularly useful, to be more precise than this. On the other hand, the value of the solar resource in space is about 3x higher than on Earth, since about ⅔ of the sun's light is blocked by the Earth during the night, or by terrain, clouds, or atmosphere. For places close to the poles, this number can increase by perhaps a factor of 10.

So even if it were possible to build gigantic solar arrays in orbit, and to capture and transmit the power to where it was needed on Earth with zero losses, the operating costs in space could be no higher than 3x that on Earth, in order to remain competitive. This is the major problem with space-based solar power. Fundamentally, the sun's light is not scarce enough on Earth, nor valuable enough on a per-m^2 basis, to make it worthwhile.

While beyond the scope of this essay, I will point out that there is no practical constraint on available area for solar panels on Earth. Solar will always use a small fraction of the area devoted to agriculture, because eating plants is about 10,000x less efficient than solar for producing mechanical work.

In fact, if we examine current and near-future commercial uses of space, the vast bulk of the industry is supported not by high power transmission of raw microwaves containing electricity, but by low power transmission of structured microwaves, containing information. The per watt value of microwaves is the fundamental question, and beaming TV, GPS signals, phone calls, and internet, is a much more sustainable business model than beaming raw power which is freely falling down anyway!

The problem with space-based communications as a a business model for space cities is that satellites are much cheaper to build and launch from Earth than to build them in space, since they are of quite small size and involve advanced, complex manufacturing.

There is an additional source of risk for long-term space infrastructure project financing, which is that not only is solar power very cheap on Earth, with a record low wholesale price of $0.023/kWh in 2018, it is getting cheaper by leaps and bounds every year. Even if a space solar power concept was valuable on paper in 2018, there is every chance that continued investment and development on Earth will lower the price so much that, like gas-powered peaker plants, a space solar power station will become a stranded asset and major loss.

Let's examine the other assumptions in turn, while bearing in mind that the total cost increase for space based power can be no higher than 3x that on Earth, corresponding to the relative value of the solar resource under the generous assumption of zero losses in transmission.

The cost of space launch must be cheap!
In 2018, the cheapest space launch was by SpaceX, at about $2000/kg to LEO. For much of the previous 3 decades, 10x this was commonplace. Yet, in "The High Frontier", O'Neill speculates that regular flights by the shuttle will reduce launch costs to the order of $100/kg. The math on reusability is much the same today, but despite recent advances in this area, improvement by another order of magnitude remains in the realm of speculation. By comparison, the cost of shipping bulk products or materials around the world on ships and trains and trucks is about $0.05/kg. At that price, an Earth-based solar panel can be shipped through every country on Earth during its production process and still have negligible increase in marginal cost compared to launching it to space.

Space-based industry must be compact!
O'Neill doesn't write from experience with industrial processes either in the 1970s or today. However, our modern economy splits machine and human labor about 1000:1 in energy terms, and as a result, any further developments for space applications will require even more automation/mechanization than is used today. There just aren't that many factories that make complicated things that aren't so big one needs a bicycle to get around. I've written at some length (https://docs.google.com/document/d/1pJzvdbtHaej9SKmNoggIrqVx-GgJO2VmpN2z2cxejPA/edit) about the difficulties of space-based industrialization, and it's not clear to me that any metal-processing nearly self-sufficient city can get by with fewer than, say, 10,000 people. The practical upshot is that throughout the bootstrapping process, the space city will remain dependent on bulk shipments of supplies from the Earth, unless and until a compact primary and secondary manufacturing paradigm can be demonstrated. It is worth stating that such an industrial system would be extremely valuable for nearly any country or city on Earth, and that despite dozens of attempts, no geopolitically isolated country has achieved it.

Resynthesis
At this point, the view is rather bleak. It turns out that O'Neill's space solar power gold mine is not viable. Does that mean the dream of millions of humans living and working in space is dead? Not quite. In this section, I explain how future technology development can help bring this vision about, through:
  • Money consumption assumption relaxation
  • Value-added manufacturing
  • Cheap launch
  • Compact industrialization

First, there is an implicit assumption that replicating the entire industrial stack in a pitiless vacuum has to make money, and on the same sorts of time scales as other large projects. Yet there is an obvious difference in scale between, say, a large bridge or chemical plant, and building an industry larger than all but a few nations on Earth. Moreover, large scale infrastructure investments are routinely made by nations with no prospect of any sort of short term return. Expenditure on health, education, defense, and other big ticket items is maintained for a variety of other reasons. Indeed, the largest expenditures by governments promote the general welfare of the nation and wider economic benefits.

I personally think there is no way to mine the moon, asteroids, or build cities on Mars and make money while doing it. I think it's worthwhile to find ways to maximize the results of a given expenditure, but fundamentally any large scale movement of humans into space will be a net consumer of wealth, to the tune of many billions per year, for decades. This expense, which is quite affordable at the national level, will employ and develop many industries on Earth, and will likely involve many of the same contractors and people as the current big ticket defense contracts do! In other words, it will not necessarily involve any new expenditures, just a slight change of course from weapons systems toward space factories.

This is not to suggest that it is pointless for cities in space to sell things in Earth-based markets, even if selling at a loss. The problem is to identify things that are worthwhile enough to bother. This is a tough problem, since nearly everything that humans needs on Earth can be found on Earth and at competitive, commodity prices. Humans in space will need to extract resources, grow food, and maintain their machines with asteroid- or moon-derived raw materials. But while such primary manufacturing is necessary to build a city in space, it's unlikely to be competitive on Earth, which has its own supply chains and breathable air.

What, then, does a good product for production in space and sale on Earth look like? It must be
  • Not readily and cheaply available on Earth. So, not a bulk commodity, like water, dirt, salt, electricity, humans, good TV, or anything in the McMaster-Carr catalog.
  • Not incredibly difficult to make, or requiring lots of human labor. Advanced composite aircraft, cars, aged care, childhood education, cutting edge silicon, medical imagers.
  • High value-added manufacturing. That is, something where the sticker price is much, much higher than the cost of the constituent components or raw materials. The German economy is built around this sort of manufacturing, and it is a comfortable middle ground between bulk commodities, on which there is no margin, and manufacturing nightmares, which require huge scale.
  • Transportable to Earth, if a physical product. So not hugely susceptible to the shocks and forces of reentry. Also, quite small in size, and with a very high value per mass. It is possible to estimate how valuable per kg something would have to be on the Moon to make it worthwhile to transport to Earth, and it's on the order of $10m/kg. This is comparable to enriched plutonium or tritium, and those markets are very elastic. That is, their value is linked to rarity. Also, the Moon doesn't have any bulk deposits of enriched plutonium lying around. With mass drivers and space cities, this cost premium would come down, but not by much. As a rule of thumb, it must be at least as valuable, in bulk, as any vanishingly scarce commodity on Earth. Perhaps the elixir of eternal life?
  • Relatively easier to make in space than on Earth. Perhaps some weird zero G crystals? Optical fibers? Unique tourist experiences?

It is hard to say in advance what advanced manufacturing might be possible and valuable in space. This is another reason to build a city in space with a primary mission of self-sufficiency, and a secondary mission of trying to be useful.

Finally, cheap launch and compact industrialization. These relate to the two main factors for the cost of building a city in space. How much stuff is needed, and how much does it cost to launch?

In my book on Mars industrialization (linked above), I estimated that a million people and a million tonnes of cargo would be needed, over several decades, to achieve full self-sufficiency. For a space city near the Earth, full self-sufficiency is not required, but overall mass requirements are higher as there is no readily available raw material. A million tonnes sounds like a lot but that's only three fully loaded container ships of the largest size. Additionally, it accounts for high technology equipment, and is separate from whatever cargo is launched from mass drivers on the Moon.

A million people and a million tonnes is actually a substantial reduction over the current state of the art, representing a further advance in mechanization of labor equivalent to the total advances to date since the industrial revolution. This industrial compactification is necessary to achieve (near) self-sufficiency in an adversarial environment, in just the same way that nuclear submarines weren't possible before steel was invented.

At current launch costs and technology, a million tonnes to LEO would require on the order of 100,000 launches at a total cost of $5 trillion dollars. If launch is to be, say, 10% of the overall program cost, and the program is budgeted at $10b/year for 50 years, then the total launch budget is $50b. This requires a reduction in launch costs of a factor of 100. To put that in perspective, that's close to the long-term goals of the SpaceX BFR or the Blue Origin New Armstrong, and could only be achieved through complete and rapid reusability of the launcher. This is not forbidden by the laws of physics, but it is a big ask.

Giant cities in space are possible, but require ongoing nation-state level funding, continued aggressive technology development in both launch and industry, and a willingness to think well outside the box when it comes to monetization.

Thursday, May 3, 2018

A new car and various lucky breaks

As I approach my first gigasecond, I've recently enjoyed noting a number of traditional "life milestones" occurring, vaguely on schedule. But just how "on schedule" should these milestones be? Given that there's only a dozen or so in a lifetime, it is reasonable to assume that there might be, among a population, some shot noise. Shot noise is where random jitter leads to apparent clustering.

So I'm excited to share that in the last six months the following good things have happened:
- C and I are expecting a sprog in August.
- C started a new job at JPL doing cybersecurity for Europa Clipper.
- We moved house to a lovely new place with awesome neighbours and lots of plants, and crucially more space.
- I started a new job at JPL developing a next generation GPS receiver for all kinds of cool science.
- We bought our first car together. It was C's first new car and my first car, and it's an electric car - the Tesla Model 3. 

It's really pretty. We accidentally drove it to the top of a nearby mountain.


It's also awesome to drive. Normally driving in LA induces tears of frustration interspersed with moments of round-eyed terror, but in the Tesla I find myself actually *looking forward* to driving. Obviously it's fast, comfortable, and has an app with which I can remotely set the interior temperature. But somehow it's more than that. 

Our previous car, a hand-me-down Infiniti G35 2005 sport sedan ("space car") fulfilled roughly the same segment 13 years ago - a fast 5 seat medium sized car with heated seats. I was just getting the hang of stick shift! Like all cars, its various features found an equilibrium that was heavy and sometimes challenging to drive, particularly in heavy traffic.

The Tesla is based on an entirely different architecture, and so its inevitable engineering consequences result in a much more driveable car. And not just because two taps on the drive stalk engages autopilot!

Of my peers I am by far the greatest laggard when it comes to buying a car, particularly in LA, where car ownership is nearly universal. For many years I was fortunate to live and work within walking or biking distance, and more recently I've occasionally used Lyft or Zipcar to go on longer trips. As someone who worked in the transportation space at Hyperloop for two and a half years, I'm keenly aware of the terrible toll that cars take on our lives and our cities. 

Cars exist as entities that are fundamentally incompatible with human bodies. They are much heavier, much faster, and much larger. The practical consequence is that designing a city that functions effectively with universal car usage and is also walkable is impossible. Even a city of any size that is car only is impossible. Like satellite internet, there is an optimal population density of about 100/sqkm (sparse suburb to semi-rural), beyond which either congestion or infrastructure costs become serious problems. Even a city like Houston, where about 70% of the land area (many billions in real estate terms) are devoted to roads, highways, driveways, and parking lots, suffers from crippling congestion. Cars can eat the whole city and still be hungry for more. 

Moreover, it's fairly clear that widespread autonomy will only make highway congestion worse, as the marginal cost of being stuck drops, encouraging yet more road usage.

But there's only so much that a lonely crusade can achieve. With our family growing and our work place being surrounded for many miles only by houses that cost many millions of dollars, some degree of driving will be inevitable. So - a car.

Why a Tesla? It's really expensive, even including the TSLA stock I bought back when it was trading at about $30/share. The trade in offered us $500 for our old car, which has a few scrapes. We could get a car worth 10x as much, such as a 2015 Prius and still be WAAAY ahead on cost. There are a couple of reasons.

First, let's consider what Tesla is trying to do, and what industry more broadly should be trying to do. Gasoline (petrol) costs, on an energy basis, about 100x less than food. This is why it's possible to run something as big and heavy as a car on a modest wage. But gasoline is expensive in other ways. Money is, in some sense, only the first moment of value. By historical accident, gaseous waste products can be dumped for free, in a way that solid and liquid wastes simply cannot anymore. 

Look ahead 100 years, or 1000 years. The world, if a sensible technological civilization still exists, will have transitioned to renewable energy. Today, newer, less harmful technology is expensive, because the customer (me) has to internalize some costs that competitive legacy products externalize. Do I mind paying a bit extra? No, not really. If people like me are prepared to open their wallets for a better future, then we have a hope. In other words, what is good for my personal enjoyment is also good for building a market demand for less environmentally destructive industry. I don't think this is a new concept, but it is a concept that needs continuously shifting targets to be meaningful.

Second, it's just so damn cool. The future is electric. Ever since I saw my first Model S prototype way back in 2011ish I've been hooked. This isn't even my first blog about Tesla. I even use battery powered power tools because I'm fascinated by wireless stuff and being able to work even where the cables don't reach. The ultimate expression of this idea is battery powered flight. Just this week, European aeroplane manufacturer Pipistrel obtained regulatory approval to sell their electric plane in the US - the first mass produced electric plane in the US. The Pipistrel has a lot of oomph, but again, think ahead. 

When I was a child, electric RC cars were a lot of fun. My brother and I salvaged a few and had many fun hours zooming them around the place. Battery powered cordless drills were also entering the market. And today we have a mass market human-sized electric car that crushes the competition. According to Tesla's earnings call today, the Model 3 is poised to become the highest selling premium sedan, and might even eventually eclipse the rest of the sector *combined*.

About 10 years the Syma 107G toy electric helicopter entered the market, and today almost anyone can save and buy a professional quality drone quadcopter. Their capabilities are already pure scifi - the Skydio can autonomously track a moving human while flying through trees and branches. Some models are designed for long flights of more than an hour, while others are designed to fly quickly through obstacle courses piloted by humans using remote radio-transmitted video. 

A few years ago I got my pilot's license flying antique Cessna 152s. The Cessna is, mechanically and electrically, stuck in the mid 1950s. The general aviation market is tough for innovators in all kinds of ways, but pushing that bucket of bolts through the sky while flying a $50 drone around my house made something click. What electric power has done for cars it can do for aircraft too. Today, of course, electric aircraft can't fly very far, but batteries are improving and there is more to flying than crossing oceans. I look forward to affordable, ecologically sound supersonic flight using electric power. 

Back to the car, for whose name I am thinking "skylab". I've been thinking a lot about manufacturing and industrialization recently. It turns out that car manufacturing is, in many ways, a gold standard of a mature industrial economy. Making cars is really, really difficult. Making them well is even harder. The Tesla Model 3 is a miracle of manufacturing. No, it's not *flawless*. There are quirks of design that are well documented, and ours has slightly bulgy headlights. It is, afterall, one of the first ever built, since I queued up on day one more than two years ago. 

Persian rugs traditionally are hand made with a small imperfection so that the artisan can avoid the envy of the gods or hubris. In some ways, minor imperfections serve as a reminder that the car did not simply spring into existence, fully formed. It was made of obstinately uncooperative atoms forged in a supernova, mixed by geological processes, mined in nearly every country on Earth, and formed together into a single shiny, fast package only by the ingenuity and effort of humans. 

When Elon Musk announced the Model 3 two years ago, mass production was to ramp up in 2020. In response to more than 400,000 reservations within 24 hours, somehow they brought that timeline in two years. There is, of course, no shortage of skepticism in the press, but let's not forget that there are very few people who could speculate authoritatively about this car even six months ago, and even fewer who would. Yet dozens of self-appointed experts have rained a constant stream of pessimism since the earliest days of Tesla, 15 years ago. "Electrical cars are impossible." "American manufacturing is dead." "Tesla will fail before 1/2/5000 units of the S/X/3 are produced." "Tesla will run out of cash." "Consumers will never spend the money." What utter rot!

The car exists. I encourage you to take a ride as soon as possible!