Next to the technical challenge, interstellar exploration projects will be amonst the largest ever undertaken and thus the question will come if it is realistic at all to get this financed. An even more interesting question is why a civilization would ever put part of its resources in such projects. In this article, we'll discuss the economics of the matter. We'll split up the problem in three parts:

  1. How much would an interstellar mission cost?
  2. Is it affordable?
  3. Who could pay for it, why and how?

The cost

We can safely assume that the first (and maybe all  - see further) interstellar missions will be done using relatively smal, unmanned, robotic probes and not by the likes of a slow version of the USS Enterprise, carrying hundreds or crew members. Not only are such probes much more affordable, it would be reckless to risk lives by sending people over without enough knowledge of the conditions they will face. Telescope observation, combined with spectrometry, will soon be able to tell if there is oxygen and water in the atmosphere of planets around neighbouring stars, but this is by far not enough information to determine if a manned mission has any hope of succes.

In the rest of the article, we will assume a rocket-type spaceship will be selected over a laser sail driven type, as the latter will require a huge in-space infrastructure which will probably not be feasible for a first mission.

The cost breaks down in several factors:

  • Research and development
  • Launch of parts from Earth into orbit and orbital assembly and/or fueling
  • Fuel cost
  • Operating costs

Some aspects of the cost are more easy to estimate than others. For example, if a first probe would be assembled in Earth orbit out of components launched from Earth, this launch cost will be proportional to the probe's mass. Luckily, thanks to commercial space launch companies this cost has dropped substantially (a SpaceX Falcon Heavy rocket would still cost about 1000 US$ per pound launched to low Earth orbit in 2014 - a reduction with almost a factor 10), and will probablly drop even further with the advent of advanced technology such as completely reusable rockets or spaceplanes such as Skylon. With these technologies, another 10-fold reduction is feasible. A large Daedalus-like probe would weigh about 54000 tons to launch to Earth orbit, which is about half the weight of a Nimitz class aircraft carrier. Thus, at current prices just launching the ship,parts including fuel into Earth orbit would could about 108 billion US$, which is about the total project cost of the international space station ISS. A launch cost of about 10 billion would be feasible with advanced launch technology. Orbital assembly is another part of the cost and is hugely dependent on the design of the ship.

Research and development costs are always very hard to estimate. The main components that require most research  are the propulsion system, a power source and a control system that lasts up to several centuries. The propulsion system is the most crucial part. However, it is not the most specific part, as many designs are based on concepts of nuclear fusion, which is also researched as Earth-based power source for electricity generation. Therefore, it is likely a lot of technology can be borrowed from existing research. For a power and control system that can operate for decades or centuries without external servicing, there is not a real precedent. The Voyager probes sent off in the 1970s come closest, and worked over 40 years relying on the sturdy electronics of the time of their construction.

Finally, as you will recall from the Rocket Equation article, a rocket needs to contain more fuel than anything else in order to be able to reach its maximum speed. Typically, 90% or more of the mass of a rocket is fuel.  You will recall from a previous article that all credible interstellar rocket concepts rely on some kind of nuclear reaction. The most affordable suitable nuclear fuel would be deuterium, which can easily be refined from sea water at a current cost of a few 1000 US$ per kg, totaling a few 10s of billions of dollars for a 50000 tonne nuclear fusion based interstellar probe. Other common fusion fuels such as lithium are similar in cost.

Highly enriched uranium or weapons grade plutonium is already a lot more expensive, at a few million US$ per kg. Production upscaling could lower the cost of this fuel, as it is produced from relatively inexpensive natural uranium  (80 US$/kg as of 2012) and is now only produces in yearly quantities of a few 100s of kilograms needed for nuclear weapons programs. Antimatter, the ultimate spacecraft fuel, is currently astronomically expensive as it is only produced atom-by-atom using particle accellarators. Generally, the all suitable nuclear fuels are currently too expensive in the required quantities except deuterium and tritium. Production upscaling, lowering cost, is possible for the other fuels but there is a problem: there will be no other driver for this then the interstellar propulsion program itself. No other use for large quantities of antimatter or highly enriched uranium exists. Therefore, the cost of the upscaling operation must be borne completely the interstellar propulsion program. In the case of antimatter manufacturing there is also a huge amount of cheap energy needed. A reasonable but still far-off source for this energy could be massive arrays of solar panels, e.g. in deserts or in space.

Considering such arguments, the few scientific studies that have appeared on this topic estimate the cost of a near-future feasible interstellar probe roughly at about 1000 billion (one trillion) US$, equal to the cost of a few medium-scale wars as fought by the United States, such as the invasions of Iraq. This was based on then-current launch technology. If launch costs to Earth orbit would drop further, and if a lot of progress would be made in nuclear fusion research for electricity production, a lower total cost could be obtainable. Also, not that this estimate is for a relatively large probe, e.g. for the Daedalus study a ship ship weighing 54000 ton, including 50000 ton of fuel and 450 ton of useful cargo, able to reach about 12%c.

Another favourable trend is miniaturization: proponents of this trend envision swarms of miniature probes taking off instead of the few skyscraper-sized ships envisioned in the more classic approach. Total launch, fuel and construction costs typically are for a large part proportional to the weight of the probe, which would make the miniature probe approach attractive. However, there are some issues with this approach too: for example, communication across interstellar distances will require quite some energy (100s of kW if not megawatts) which a miniature probe will not be able to provide. Also, equipment such as telescopes, planetary landers etc. is not easily downscalable. Therefore, our estimate is still that a first-generation interstellar probe would carry a few hundreds of tons of useful cargo and thus, by the rocket equation, would weigh at least 10000 tons.

Once launched, the operating costs of the missions would be relatively small and comparable to that of other deep space missions. The main cost would be the upkeep of a communication link. For the Voyager program, this comes down to about 15 million USD per year.

Is this affordable?

We can now compare the estimated cost of an interstellar exploration project with what the current economy produces to see if it is anywhere near realistic. The gross national product of the world, that is the total value of all goods and services produced, was 72 trillion US$ in 2012. Of course, a significant part of those goods were essentials such as clothing or food. Nevertheless, as the average economic growth is still about 3% per year, which is much larger than the population growth, the amount of discretionary spending is increasing. An example of discretionary spending that could be turned towards the projects is military spending. For example, the Iraq war (2003-2011) cost the United States about 1.7 trillion US$. A definite plus to tap the military expenditure for space projects is the fact that the military aerospace industry would be easily converted. Other examples of nonessential luxuries our current economic system produces: the world pet food market goes at 60 billion US$ per year (Max can eat Europe, over 200 kg food per person per year is wasted anyway), soccer bets (tens of billions of US$ per year) luxury cars (BMW alone has a yearly revenue of about 80 billion €) and so on. This is not to say we believe no one should enjoy any luxuries, but to indicate that right now humanity can very well afford to spend a few tens of billions per year on an interstellar project if this is deemed necessary.

In the Daedalus study of the 1970s, it was assumed that humanity would not launch an interstellar probe until a solar-system wide economy had been set up. In such a scenario, humans would spread around to live on Mars, the Asteroids and in space stations and would use the resources of those locations. The resulting economic output of the solar system would be so huge, it could easily afford the construction of a trillion dollar interstellar probe. The necessary space infrastructure would be there already anyway. However, these scenarios failed to come true.

Similar scenarios were drawn up envisaging human colonies underseas, and those did not come true either. It seems the scenarists of the time were  underestimating the dependence a human economy has on a suitable ecosystem, the difficulty of a relatively small group of people to thrive with limited and expensive supply lines to the rest of civilization, and the possibilities of remote control and automation. Nevertheless, significant resources such as oil and gas are now being harvested from deep waters, and the first projects for asteroid mining are being considered. There is little talk left about almost endless exponential growth of the economy. To be complete, there is still talk about such a thing amongst believers in the Singularity, a point in time in which artificial intelligence and/or robots would take over the reign of humans as dominant species on the planet. We will assume this will not happen, or not be allowed to happen.

In this light it is more likely that humanity will launch its first starship while a vast majority of humans is still living on the Earth. Thus, an important factor is the amount of resources humanity can produce on Earth. Seen the timescales of interstellar projects, only relatively sustainable economic production should be considered. We estimate this will not be more than about times the current global GDP, based on the relatively slow growth in developed industrial countries, the population growth stagnation as predicted by the UN and the population of the developing countries.

As argued above, even with the current global GDP it could be possible to harness tens and (if a truly global cooperation can be achieved) even a few hundreds of billions of dollars for a cause that is seen as important. Which brings us to the most important question: how to convince enough people that this is important? Why would anybody prefer to spend resources on this instead of on a more pressing need? How, in the prespective of the interstellar exploration advocate, to gather the resources for this cause?


Who would would pay for this and why?

In society, a lot of things are done for financial profit. Some regions even have been colonized for profit generation, for example for establishing large plantations. Would this be a model that can finance interstellar expeditions? The short answer: no. The many hundreds of years to get there and back again withold any investor from pursuing the already risky and extremely expensive enterprise.

However, there are lots of things that do not generate direct financial profit and that are done anyway, because people, organizations or countries find them important. For example, the Large Hadron Collider at CERN cost billions of Euros and was constructed mainly for the purpose of finding the Higgs particle. The scientists that organized the enterprise were able to convince their governments to sponsor this experiment because of the fundamental value it represented: a better understanding of the universe.

So, rest assured it is possible to find sponsors, governmental or private, if there is a good reason to do so. What reasons?

  • Finding and studying life elsewhere in the universe.
  • 'Seeding' life from Earth on suitable planets where there is none, safeguarding us against extinction events that can happen at any time (meteor crashes, nuclear wars, ...)

For achieving this, there is no alternative then to travel to other stars. This gives interstellar travel a unique selling proposition. Then, there are other not-so-unique reasons such as prestige, promoting science, education, potential spinoff technologies and fighting stagnation and complacency: much more than any other grand project interstellar expeditions would inspire billions of people. 

There are also a few unique difficulties with interstellar expeditions:

  • The huge cost of starship construction, followed by a period of many decades during which the ship is underway and not much expense is needed
  • The very long timescales - someone sponsoring or working on the project in the early phase is likely not to see the end of it.
  • The fact that there is pressing need, as those distant planets will be there in a 1000 years just as well.

In a campaign to promote the idea of traveling to the stars, these points must be addressed. The last two issues are a matter of the right framing: if people get convinced that we should build starships, they will also be motivated to want to contribute to the cause in their lifetime. Similar to the work of craftsmen that built the great cathedrals in Europe over the course of many generations, this work will far outlive any contrubuter and give extended meaning to their existence. The huge timescales are not per se only a disadvantage, but also will tie generations together.

The final point is how to finance the huge construction cost and organize the project. For this aspect, the long time the voyage will take is actually an advantage as well. The necessary research and construction of the ship can be spread out over several decades without prolonging the centuries-long project much. The capital needed for constructing the starship can be built up over several decades as well, in parallel with the research phase. For example, if all major space agencies (NASA,ESA,...) could be convinced to invest 10% of their budget in the fund (e.g. in return for a controlling stake in the organization), about 3 billion dollars would be fed into the fund yearly. Assuming a yearly return of 1.7% above inflation, the same average as the Nobel Foundation achieved over the past 110 years, it would take 110 years to reach a target capital of 1000 billion.

Again, the main necessity for humanity to travel to the stars is to set up a right frame of mind, valuing long-term thinking.