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Costs of an Interstellar Probe

When does it make sense to build a starship? Back in the late 1960s, Freeman Dyson went to work on the question of how much an interstellar probe might cost. Extrapolating from nuclear pulse propulsion and the state of the art in spacecraft design as then understood, Dyson arrived at an estimate of $100 billion to build the craft, which translates into roughly $650 billion today. Though stark, that figure is by no means as eye-popping as one of the estimates drawn up by the original Project Daedalus team: $100 trillion in 1978 dollars.

These figures numb the senses, and you may recall the recent work by Ralph McNutt (Johns Hopkins Applied Physics Laboratory) and team, which pegged the cost of a series of human expeditions into the outer Solar System at $4 trillion. It’s helpful to remember, though, that calculating when a project becomes fiscally feasible can be a useful undertaking in itself. Richard Obousy goes to work on these matters in a recent post in the Project Icarus blog, trying to figure out how long it would take before our civilization has grown to the point that the expenses we are talking about today would become manageable.

Starships as Percentage of GDP

Obousy’s assumption is that it will become economically feasible (and just as important, politically viable) to construct an interstellar craft when the total cost represents no more than 1% of the Gross Domestic Product of the constructing nation. Now the GDP of the United States, a measure of the country’s overall economic output in a given year, is currently $14.6 trillion. The GDP of the entire planet is now $61.1 trillion, and the option of consolidating the larger amount in these calculations is obvious, so Obousy looks at his figures in terms of the US economy and contrasts those results with the global perspective.

The outcome: The US economy becomes able to support a Dyson-class starship costing $650 billion by the year 2085; i.e., in that year, such a cost represents 1% of GDP based on a 2% growth rate per year. A Daedalus-style craft becomes feasible no earlier than 2340. In global terms, the Dyson starship could be built (assuming the global cooperation we at present do not have) within the next few years, whereas the Daedalus class craft would have to wait until 2268. Note that we’re basing all this purely on percentage of GDP and an estimated cost for a craft whose core technologies have not yet been developed. In other words, we’re brainstorming.

And if we achieve a compounding global GDP of not 2% but 4%? In that case, things move more quickly, and we might aim at a stripped down Daedalus (in the $20 trillion range) sooner:

Compounding the Global GDP at 4% returns a date of 2099 for when construction of the ‘Budget Daedalus’ represents only 1% of the planet’s GDP. Thus it is, in some sense of the word, possible that our transition from the 21st century into the 22nd century will be celebrated with the construction of Earth’s first interstellar explorer. An exciting and delightful end to this century, one has to admit.

Powering Up a Lightsail

Projections for the cost of interstellar missions vary widely. Curt Mileikowsky, who at the time he delivered his talk on the subject in 1994 was serving as Sweden’s director of technology, analyzed an interstellar probe mission that would travel at one-third the speed of light and be built around a laser-powered lightsail. His figures were likewise daunting, involving the need for 65,000 billion watts of installed electric power capacity to power up the laser and deliver the needed acceleration to the craft. The cost: $130 trillion for electricity alone.

But Mileikowsky, who spoke at the “Interstellar Robotic Probes: Are We Ready?” conference in New York hosted by Ed Belbruno, noted the same point Obousy does. Economies are not static entities, and these huge figures may one day be justifiable within the context of worldwide growth. No one should be sanguine about that growth, but on time-scales of centuries it is not reasonable to rule out projects that today’s economy could hardly support.

We can hope, too, for the kind of conceptual changes that bring interstellar flight to a more manageable level. Speaking at the same conference as Mileikowsky, Dana Andrews (Andrews Space) analyzed the cost of fusion missions powered by deuterium from the outer planets, coming up with a future cost of $15 million per mission, which is the most optimistic scenario I’ve seen. Andrews runs through the analysis in “Cost Considerations for Interstellar Missions,” JBIS 49 (1996), pp. 123-28, explaining the assumptions that got him there.

Interstellar Design and Infrastructure

But back to Obousy, who in the course of discussing motivations for eventual interstellar flight — and taking the long-term perspective so favored by Centauri Dreams — places our starship building in the context of a developing infrastructure in space:

Underlying all of these assumptions is the belief that the solar system will in time, become the domain of an all encompassing, profoundly well organized commonwealth, with a vast economic and productive capability. Perhaps the enterprise of starship building, gargantuan by today’s standards, may be one of the few that is demanding enough to keep the community engaged. If history is to serve as a reliable yardstick, evidence indicates that new technological innovations tend to catalyze productivity, which is further used in the creation of armies, empires and opulent masterpieces of stone, steel and canvas. Starship construction may serve as a welcome alternative to these historic follies.

Or perhaps not so much an alternative as yet another option our species can use to continue the investigations that scientific curiosity and the human imagination have fueled. We are at the point in starship design where early 19th Century engineers were in imagining craft that flew in the air. Surely if birds flew by flapping their wings, so should an artificial aeroplane, and as for power, we have the admittedly heavy steam engine… Project Icarus is important because it seeks to push current technologies ill adapted for interstellar work to the next level, just as later 19th Century designers would re-think powerplants, camber and ailerons.

Cost, then, is just one of the interstellar imponderables. From our current vantage, we can get just a glimpse of the magnitude of the task, but must continue seeking ideas that will reduce not only the expense but the time of the journey. No one said building starships would be easy.

The Dyson paper is “Interstellar Transport,” Physics Today 21 (1968), pp. 41–45. And you can find Curt Mileikowsky’s work in “How and When Could We Be Ready to Send a 1,000 Kg Research Probe with a Coasting Speed of 0.3c to a Star?” JBIS 49 (1996), pp. 335-344.


Comments on this entry are closed.

  • kzb July 1, 2010, 12:57

    Frankly I think this kind of analysis simply shows up the shortcomings of economic performance indicators and their relationship to the real world.
    Much of the “growth” is illusionary. In the US and UK, it has come from an unsustainable credit bubble. If you remortgage, because your property has magically increased in value, and buy an imported car, the economy (GDP) is judged to have grown as a result. It’s a nonsense.
    If we extrapolate even further into the future, our descendants will be able to buy an interstellar trip out of the loose change in their pockets.

  • Ron S July 1, 2010, 13:05

    Focusing on cost, either as an absolute or as a % of economic capacity, is a bit misleading. If the population is motivated by some purpose, the 1% figure is no barrier. Consider the military and health care, which the people of many countries happily support at a far higher GDP %.

    There are then two options to fund an interstellar probe:
    1) Bring a large part of the populations of the most-developed countries on side. This will not be easy, and perhaps next to impossible. You and I may be willing, but the reasons that motivate those of us who are already inclined in that direction are not those that would motivate a majority of the population.
    2) Keep investing in basic R&D until such time that the cost is lowered to well under 1%, to a sufficiently low level that voters see the expense as merely an annoyance and not a mis-allocation of funds from other, preferred programs. Forecasting this is only possible if one has an almost religious belief in technology trend lines and the willingness of our descendants, perhaps several generations removed, to take the plunge.

  • JohnHunt July 1, 2010, 14:22

    What would be the cost of launching the smallest possible interstellar probe? I doubt that any of the cost estimates mentioned above take into account what the budgetary impact would be once nanotechnology is significantly developed. But certainly it will…and probably before the end of this century.

    I think that it is wasteful and even counterproductive to discuss and plan for massive interstellar ships while fairly neglecting alternative schemes which would logically cost less and therefore likely be developed first.

  • NS July 1, 2010, 15:03

    Dunno. In the 1500’s you could send 5 ships to the Far East for a load of spices, and even if only one of them got back you still made a profit. There might be similar resource potential elsewhere in the solar system, but it’s hard to see how interstellar trips would yield anything close to that. Unless things change drastically I suspect investment in interstellar travel will be at the same levels they currently are for deep space exploration (low).

  • Spaceman Beren July 1, 2010, 17:12

    If we had the capability to harness solar space energy using materials that were not deep in our gravity well, then there is a superabundance of power available ( not to mention the lower costs for materials provided by access to such space based resources). The cost in materials and energy could be conceivably 1/1000th what they are now if construction was at the peak of availability. This only leaves the expertise and human resources as major cost drivers. If we provided longer, inexpensive, and more accessible education we could lower those costs as well..

    I’m not quite sure why this hasn’t been touted as a goal for NASA already. Robotic resource extraction, space based factories and more science would allow us to break the tether of our cradle quite quickly.

  • Zen Blade July 1, 2010, 17:23


    The important thing to remember is that the far east had goods that the west did not possess. So, we would need to find something cool out there that we can’t get on Earth… at least for now.

  • Bounty July 1, 2010, 18:59

    Why make the figure baseed on 1 year of GDP? It would take several years to implement. Figure the F-35 Lightning II program is a “300 billion” dollar program and it’s getting funded right now. Any funding needs to be thought of in multiple years. Also in multiple stages. Things like fuel may not be strictly for this probe, it might be shared by other interests. Hopefully the fuel infrastructure would be built up years ahead for domestic projects and funded by them etc.

    The sad truth is NASA’s budget is closing in on 19 billion a year. As a % of GDP I believe it’s the lowest it’s ever been and going down. Sheeple would rather live another few years dragging out their existance than live an interesting life.

    Maybe we need to think of the problem of cost longer term. Either some kind of (awsome!) account that gets 50 mil added every month for the next 100 years or 500 million a month worth of NASA budge, and we start building things for the next 100 years.

    Hmmm add a few miles worth of sail material every year for the next 50 years, then do 10 years worth of science package (lens/antenna first, chip/software last), launch it, then add laser power / focusing (from earth) over the last 40 years… plus another 100 years for data return.

  • Matt Robare July 1, 2010, 19:56

    Zen Blade,

    Not necesarrily something we can’t get on Earth, just something which either in abundance or ease of access is better than here.

    I think there are going to be two major stages of commercial exploration: firstly, there will be an orbital stage which sees the building of an infrastructure: solar power satellites, construction facilities and even robotic manufacturing plants. Space based solar power alone would result in another industrial revolution as most things could switch over from fossil fuels to pure electricity. The second stage would feature the exploration and exploitation of Near-Earth Objects, which has hardly begun. As we reach each NEO we’ll take what we need from it and leave behind essentially a space station, a stepping stone to the next NEO.

  • Adam July 1, 2010, 20:02

    Much of the cost comes from the freight charges to space! At $10,000/kg to LEO that’s a major expense up front. Launching 54,000 tons of “Daedalus” would thus cost ~$540 billion from that alone. Multiply several times for all the other costs and the trillions mark is crossed very quickly.

    A 2003 study by Dana Andrews for an interstellar probe using Jordin Kare’s Sail-Beam to get to 0.1c had a peak power of 30 GW of laser. Assuming very efficient lasers (30%) means at least 100 GW of space power is needed, which from solar power satellites massing ~5,000 tons/ GW means at least 500,000 tons of power satellite… Which illustrates the difficulty again. Everyone talks about mining the Moon etc. But how many hundreds of thousands of tons of power-sat factory will be needed on the Moon to produce 100 GW of power satellites? No one seems to be able to produce realistic numbers to back up the supposed ease of getting resources from the Moon.

  • Zen Blade July 1, 2010, 21:16


    The ease of access (currently) is non-existent. Unfortunately, I am not optimistic that things will get easier in the near/foreseeable future. After all, the US will now be reliant on Russia sending our men and women into space.

    This development may just be the next logical step in space exploration evolution, BUT it could also be a regression because of the prohibitive costs and realities of space exploration.
    We may no longer the largest tent-pole…

  • Mark Meier July 2, 2010, 6:33

    Some of the commentary here has been critical of the numbers presented in the article. Hey, lighten up! These are pretty numbers — put them out there and admire them for what they are. Nobody has said these numbers are carved in stone, but are merely the best guess we can put forth at this time based on what we know now. Sure, there is a LOT of guess work, but every big idea starts with guessing. Zero in on the specifics at this point and we don’t even have pretty numbers.

    As I mentioned before, lighten up — enjoy the process.

  • Tobias Holbrook July 2, 2010, 8:29

    “Much of the cost comes from the freight charges to space! At $10,000/kg to LEO that’s a major expense up front. Launching 54,000 tons of “Daedalus” would thus cost ~$540 billion from that alone. Multiply several times for all the other costs and the trillions mark is crossed very quickly. ”
    Really? I’ve always thought of starship construction as being something that takes place in a fully developed solar system, and a natural evolution of transportation – chemical to nuclear to lightsails to fusion. In which case we’d be looking at a lot more than 1% being plunged into it…. how much of the Terran GDP is invested in developing transport?

  • Scott G July 2, 2010, 9:00

    The comment about NASA’s budget by reader Bounty is worth elaborating on… It turns out “NASA Budget” has its own Wikipedia page – which holds a record of the agency’s budget for every year starting in 1958. As a percentage of the overall US Federal Budget, NASA’s portion IS almost the lowest it’s ever been (currently at 0.52%) since about 1960. It appears that NASA’s budget topped-out at 5.5% in 1966 (during the main thrust of the Apollo Program).

    So, as far as achieving a national-will for funding an interstellar probe, I think it does very much depend on whether or not the spaceflight community can do a good job at motivating the general public to support such a mission.

    In short, if we find a compelling-enough reason to go to another star (such as finding unambiguous bio-signatures on a nearby planet), then I think the US, or another of the world’s space agencies will be able to make the case that we should fund a mission to go there. Without a compelling reason, we’ll never muster the political will to do so — even if the cost is less than 1% of the federal budget — as is currently happening with the cancellation of the Space Shuttle Program and it’s successor!

  • T_U_T July 2, 2010, 16:42

    I think that such estimates are all orders of magnitude over the mark because they ignore the economies of scale that would kick into action if someone actually started such gigantic project. For example if you aimed at the ‘super orion’, you would NOT build 1e6 ton of steel on the market, you would build a few huge automated steel mills around an iron ore deposit, and extract it at virtually zero cost. You would not buy electricity, you would build your own dedicated nuclear power plant powered by the same uranium you are going to use in the ship drive. The uranium would be extracted from seawater by an automated plant that, once started, is self-supporting and can go on forever at only maintenance cost. And so on. This way, you would have the ‘super orion’ at the cost of one ocean liner, two nuclear reactors and a few steel mills. Which is virtually nil compared to the overbloated estimates in the article. Oh, also, you would build it in africa, where people work almost for peanuts, bringing employment, peace, and net positive economic growth, paying at least part of the cost, driving the price down even further.
    All the technologies needed for a super orion ship are already developed and mature, there is no need to wait till we are ready.
    On the contrary. Waiting till ‘our technology is advanced enough’
    is like if someone declared ‘I won’t start with weight training until I get strong enough to lift the biggest weights without too much effort’. Of course you never will actually.

  • T_U_T July 2, 2010, 16:44

    …NOT buy 1e6 ton of steel

  • Adam July 3, 2010, 2:57

    Hi Tobias H.

    If you look at what I said as a “reductio ad absurdum” argument against the idea of starprobes being developed (and costed) in a vacuum, metaphorically speaking, then you’ll see we’re saying basically the same thing. Star-probes only really become viable in a developed solar economy when they’re on the scales being discussed in the literature. Even the 10 ton Sail-Beam probe needs ~megatons of infrastructure/raw-materials manipulation to develop the required power systems for propelling it to the stars… assuming mere extrapolations of current technology.

    However consider the “Daedalus” 1st Stage main engine. It masses ~300 tons (ignoring the fuel handling etc.) and produces some 40 TW of jet-power. An induction coil system tapped that jet-power for 675 GW of power to energise the ignition system. To produce the same amount of power (40 TW or even 675 GW) for a laser-sail probe would need immense solar-arrays or very big convential fission reactors, adapted for space. Starship engines potentially point the way to the transformation of human activities in space, but their development won’t be easy.

  • david lewis July 3, 2010, 8:06

    When calculating such costs one should also remember that that money is not being just cast away into space. It would go into paying workers who would then be taxed. Those workers would then with the money left after taxes buy goods. The providers of those goods would then be taxed. Those providers would then have to pay their workers, who would be taxed…..

    The money spent to try and revive the economy could have been spent this way. Rather than large payments to banks and major corporations it could have been spent in hiring and paying thousands of workers for such a project. As people bought goods and paid their mortgages the money would still have ended up in either the hands of government again through taxes or in the hands of the banks and major corporations. Stimulating the economy in such a way might have ended with such a project having a net cost of zero or better.

  • higgy July 5, 2010, 9:25

    Nice article.
    But babysteps are needed. We need to start developing LEO operations and Lunar operations. Instead of harvesting resources from Earth, we can collect those resources from Lunar sources or from asteroids. Costs will be reduced with the developement of orbital or Lunar factories.
    We should worry more about gaining control of our local system before we attempt to send a probe to another star system.

  • JohnHunt July 6, 2010, 11:45

    > No one seems to be able to produce realistic numbers to back up the supposed ease of getting resources from the Moon.

    Adam, I don’t have hard numbers but here is a pathway to get there which would be more economically viable than just jumping directly to launching power stations in support of an interstellar mission.

    First, don’t start by trying to produce Power sat factories. Go for the low-hanging fruit first. Believe it or not, lunar rock collectibles might be the first market and could profitably earn something like $6 billion before market saturation. But next would be harvesting lunar water ice and transporting it to LEO via reusable “water trucks” (with aerocapture). NASA would probably be the main purchaser but GEO telecom companies would too. Next would be extraction of metals from regolith and transport to LEO or GEO after turning them into trusses. As I understand, much of the power to heat ice or regolith would come from parabolic (trough) mirrors. At this point, we are within reach of producing the heavy parts of solar power sats which allows us start carving out a portion of the multi-billion dollar energy market. Along the way we start benefiting by economies of scale where development costs are spread out.