Fueling Icarus

Icarus probe passing Jupiter (Michel Lamontagne)

Icarus is to be a fusion powered starship.  To keep the ship’s mass within reasonable bounds, the fusion drive will have to be very powerful, transforming about 100 grams of fuel into 100 tonnes of thrust every second.  Just how powerful is that?  Well, the designs that emerged from the recent Icarus workshops vary from 15,000 to 30,000 GigaWatts of power.  This is an improvement over the Daedalus design, which powered up to 42,000 GW, but it nevertheless rivals the average power use of the entire Earth population, which was 18,000 GW in 2010.

Skeptics might, at this point, be justified in wondering if the starship designers have collectively lost their minds — especially if we consider that the drive is supposed to operate for up to fifteen years continuously at full power output.  Using terrestrial energy costs, this would yield an energy cost, in 2014 dollars, of $8 trillion per year, or over $120 trillion for the whole mission.

There has to be a catch somewhere, right?  Or is it really expected that the cost of energy will go down something like 100,000 times, so that the average per capita cost of energy, that is about $650 per year today, will be about half a penny by the turn of the next century?  Will fusion power really be that cheap?

No. Fusion power will probably never be so cheap.  But, yes, there is a catch.  And it lies in the difference between the cost of producing energy, and the cost of using energy.

“Free” Energy

It is sometimes said that fusion holds the promise of free energy. But we already have free energy.  In a hydroelectric power plant, the energy is as free as it can be, provided by the potential energy of water lifted higher in our gravity well by the Sun; yet hydroelectric power can still be expensive.  This will be true for fusion reactors as well.  Beyond the original energy source, there is the system required to convert that energy to electricity or hydrogen gas for distribution, the cost of the distribution infrastructure, land for power lines, cooling systems, and the water rights that come with them. The fusion fuel will also have production costs, however minor.  So even if the energy is free, it will cost something to deliver it to the consumer.  In fact, energy is often free.  Creating the power and distributing the energy is what costs something.

Despite these costs, distributed energy itself is already pretty cheap today. In the North American market, for example, energy is almost too cheap to sustain itself.  The low price for energy has made the construction of nuclear reactors uneconomical, and now the low price of natural gas and of gas turbines is making coal an unattractive solution.  The brownouts in California a few years ago resulted from a market that made building new power plant too expensive, such that the power system became fragile and unable to meet new loads.  Québec, once a mecca for aluminium production due to cheap hydroelectricity,  is outclassed by Dubai with its nearly free gas. Yet what could be freer than falling water? Again, it’s the dam and the power station that can make Québec’s hydroelectric power uneconomical.   Electrical energy may be expensive in parts of Europe today, but mainly because it is used to finance the construction of very capital intensive energy production equipment, wind power and solar farms.  The real cost of energy is the cost and financing of the energy production and distribution infrastructure, of safe construction and redundant systems — not the energy itself.

That is the catch that resolves the Icarus power dilemna:  Icarus is practically pure energy production, and it produces this energy with an incredibly compact power source, with a relatively cheap fuel.  Furthermore, it requires absolutely no distribution infrastructure.

The Icarus spaceship, un-fuelled, will weigh barely more than a small frigate, or a 10 to 20 story building.  Dry mass is between 1500 and 5000 tons.  This is a fraction of the weight of even a single nuclear power plant today, or of a large wind farm.  Even if the weight is composed of exotic materials and hyper sophisticated electronics, it’s just not that much material.  In a way, Icarus is barely more than a big nuclear power core, with almost none of the shielding, cooling, turbines, concrete, wiring, land and  power sub stations, pylons or much of anything else. All the expensive stuff is left out.

So the energy that Icarus uses will be, relative to its tremendous quantity, practically free.  But it will also be completely unusable for any other purpose than the propulsion of the ship, devoid of any of the infrastructure required to turn it into a valuable product.  So it will be both free, and, in a sense, worthless as well.

This raises a new question: does it make sense for the society of 2100 to use up deuterium as a fuel for a starship, where it produces no value, rather than using it in fusion reactors on Earth, where it would produce usable energy?  Can this future society afford to ‘waste’ all that fuel?  What will be the cost for deuterium in 2100, and will there be any available for space exploration?

Energy Demand

Power distribution in India (Pakistan today)

To get at this, we first need to determine what we can expect from world energy demand in 2100.  This is a highly speculative endeavor, but one that can be done simply with a few conservative assumptions.  We start with a look at today’s numbers, to understand the basis of our projections:

Information from Wikipedia

The most important number is the first one, population.  The median value for the world population in 2100 as proposed by the United Nations is 10 billion, a nice round number (2).  This is a 30% population increase in 90 years, a fairly slow rate. If all else were to remain equal, the energy demand in 2100 might not be much higher than it was in 2010.  Of course, all else will probably not remain equal. 

On one hand, we should expect (and hope) for energy consumption per capita to go up, as a direct corollary to the increase in living standards in developing countries.  This is already the main driving force behind the energy consumption increases of the last three decades, as shown the graph below.

Source: Wikicommons

On the other hand, we should also expect (and hope) that technological innovations will tend to drive the energy consumption per capita in all countries down.  As we head slowly into a production system based on recycling rather than exploitation of new resources, energy costs for heavy industry should go down.  We have been spending hundreds of billions of dollars to remove oxygen from iron ore and aluminum bauxite, but once that is done, reuse takes a fraction of the power requirements. 

More efficient energy production will also reduce the rate of energy consumption. For example, producing petroleum from the Alberta tar sands in Canada requires up to a third of the energy that the oil alone will provide. Huge volumes of natural gas are burned to supply steam for injection underground, to liquefy the oil. This rather absurd method of production is only practical because natural gas in very, very cheap and abundant, and petroleum is presently the most practical energy source for cars and trucks.  But electrification of transportation could cancel most of the demand for petroleum, likely making tar sand oil production itself un-economical. The aforementioned natural gas would be more efficiently used to produce electricity directly, reducing the net power requirements of light cars and trucks by as much as 75%.

Another possibility for energy use reduction is heat pumps.  In many climates, heat pumps can reduce the energy use for heating by 60% and more. Equipment costs have thus far retarded the proliferation of heat pump technology, but if energy costs were to rise, investments in energy reduction would become more interesting, encouraging investment in more productive installations, rather than cheaper ones. 

So it is possible that, despite large improvements in quality of life and increases in energy use in most countries, average energy consumption per capita might not rise too terribly much by 2100. Here are the results of this conservative/optimistic scenario:

Although the population has risen by 30%, the energy demand has more than doubled.  Energy demand certainly rises, and producing all that energy will require new infrastructures, but the demand is still in the same order of magnitude as today’s requirements.

Energy Sources

Most of today’s energy comes from oil, coal and gas combustion.  It seems unrealistic and possibly catastrophic from the environmental point of view, to expect to meet the rising global energy demand using primarily fossil fuels. It seems likely that natural gas will remain a practical energy source up to and perhaps beyond the end of the century; however, it would be good, and probably unavoidable, to phase out coal and oil.

Does this leave an opening for fusion? Is fusion an automatic winner in the competition between new energy sources?  The answer to these questions will come from the costs of fusion power plants, which are still very much unknown.  However, after 40 years of very slow progress, it seems likely that fusion power plants will be large, heavy, expensive, and complex. Terrestrial fusion power is unlikely to come online for several more decades.  If ever.

Cheap solar power and good batteries, when they eventually come along, might effectively kill fusion forever as far as consumers are concerned. The development of really cheap solar — of the “paint it on the wall” type — seems just as likely, or perhaps even a little more likely, than large fusion power plants.  The quantity of available solar energy on Earth is staggering: over 2000 times the energy requirements projected in the table above for 2100.  The quantities available in space are millions of times larger.

Thorium nuclear reactors are also an alternative to fossil fuel and fusion.  Potentially less expensive, safer, and easier to build than classical nuclear reactors, they are basically waiting for an increase in the cost of energy to become viable.  These may offer a perfect complement to distributed solar power, offering safe base load power for the power grid and industry.

Mr Fusion, from Back to the future II

Small and cheap distributed fusion might change the equation, turning power production from a utility to a consumer product. But none of the attempts in that direction have produced any results.  By all rational projections,  the path to fusion seems to require large and expensive infrastructures. No Mr. Fusion in our future, unfortunately.

Therefore, it is quite possible, perhaps even likely, that the demand for deuterium for power generation on Earth in 2100 will be nil.  And so the only cost for deuterium may be its production cost.  It will have no other value — at least on Earth.

Deuterium Production

Girlder Sulfide process heavy water extraction towers (Candu)

What is the cost of the fuel for Icarus?  A quick Internet shopping hunt will lead us to laboratory supply companies selling compressed gas deuterium at about $75 per kilogram (3). So the 70,000 tons of deuterium for Icarus would cost about $5 billion if bought from one of these lab supply stores.  We should expect large scale production to bring these costs down, but perhaps not by much if the infrastructure can’t be used for much more than fuel production for spaceships, and energy is already a large fraction of the cost of production (4).

The concentration of deuterium in the sea is 1 atom of deuterium for every 6400 atoms of hydrogen.  Most of it is in the form of semi-heavy water, or one deuterium (atomic mass 2), one oxygen (atomic mass 16) and one hydrogen (atomic mass 1).  So the molecular weight of semi heavy water is 19, and 70,000 tons of deuterium will require 1,300,000 tons of semi-heavy water, extracted from 8 billion tons of water. If we spread this over a period of 10 years, then our deuterium production facility will need to process about 23 m³ of water per second, or 420,000 gallons per minute.  To compare, this is about the flow of water used for cooling a single mid-sized power plant, be it coal or nuclear.

So the entire production of the deuterium supply for the Icarus might be the 10-year work of a single installation, about the size of a modern power plant, located somewhere along the seashore.  It would make sense to locate the plant close to the spaceport used to deliver the fuel up to space.  This power plant would be one of the 25,000 plants, or part of 100 million or more small power systems, supplying electricity, and perhaps hydrogen, to a world population of 10 billion people, sometime around the year 2100. From that perspective, the fuel costs seem rather insignificant.

(1)http://en.wikipedia.org/wiki/World_energy_consumption

(2)http://en.wikipedia.org/wiki/World_population

(3)http://www.sigmaaldrich.com/catalog/product/aldrich/368407?lang=en&region=CA

(4)http://www.media.cns-snc.ca/Bulletin/A_Miller_Heavy_Water.pdf