Is the ISS the most expensive single human artifact ever, after adjusting for inflation? Well, to start with, it's a whole lot more expensive than a medieval cathedral anyway. First we need an estimate of the cost of the ISS, and this article in the Space Review estimates the total cost up to 2015 as $150 billion (in 2010 dollars). That's the total cost including all the international partners. So, how much did it cost to build a medieval cathedral?

There's an estimate here that the cost of rebuilding Chatres between 1194 and 1223 after much of it was destroyed in a fire amounted to around fifty million 1972 US dollars adjusted for inflation. Or around $260 million in 2010 US dollars. That's a conservative estimate though, and for a rebuild, not a build from scratch.

There's another estimate here, based on detailed accounts of the years worked by labourers. Santiago cathedral used a workforce of 50 skilled labourers from 1075 to 1211. So, that's around 6850 labourer years. The average US wage for a stone mason is around 40,000 dollars, so that works out to around 274 million dollars. Converting back to 2010 dollars, that's around 250 million dollars. That's just the labour, you also have to pay for materials. They estimated an equal cost for the materials. So that's around a half a billion dollars.

So, if that's a good rough estimate, you could build three hundred medieval cathedrals for the cost of the ISS. Even if that estimate was an order of magnitude out, it's clear that the ISS is way more expensive than a medieval cathedral.

Please don't take this article too seriously. I know you can't really expect to come up with an accurate direct comparison of the cost of a medieval cathedral with the ISS. It is just a rough first attempt at answering an almost unanswerable question.

Here, we have over two orders of magnitude difference, so as a rough ballpark, it would seem likely that the ISS costs a fair bit more.

Another possible criticism - the space review estimate includes on going costs up to 2015, so not just the cost of construction, but also maintenance and cost of living in it, doing scientific experiments etc. If you remove the shuttle flights, it's a little under $100 billion, but some of those flights were also used to carry modules up to LEO and the astronauts were needed to build the ISS, so some of the space shuttle flights have to be included. And some of the international contribution doubtless could be removed.

Taking account of that, the actual cost of building it, perhaps more like $100 billion. So I'll use that instead for the rest of these examples. So that is two hundred medieval cathedrals, approximately.

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LET'S TRY SOME OTHER EXAMPLES

There's an estimate here for the Great Pyramid, that it would cost 878 million dollars in today's money - that's building it today with the current cost of the limestone and the labour.

What it would cost to build the world's most famous landmarks today

Kheops-Pyramid Great pyramid of Giza, 878 million dollars if built with today's materials and modern labour, build 114 of those.

That's the best I can find there. We could rebuild 114 great pyramids for the cost of the ISS. But most of the cost there is for the limestone, using modern prices for limestone.

Of all the examples I found, this is perhaps the closest in actual cost to the ISS. It would be interesting if anyone has tried to figure out what it would cost the ancient Egyptians, for instance as worker years, including the time taken to quarry the limestone using their own technology.

For some more examples the Vraat Ramayan Mandir, a Hindu temple, will cost 500 Core, or around 76 million dollars to build, and will be the largest religious monument in the world. It's also roughly modeled after Angkor Wat, an ancient Buddhist temple in Cambodia, and double its height. So that gives a rough ballpark figure for that also.



However, adjusting for the purchasing power parity, that one dollar in India will buy goods equivalent to 0.3 dollars in the US, then perhaps to compare with the ISS, it's more like 253 million dollars. That's using modern technology of course. So the ISS is, very roughly, 400 times the cost of this temple.



The ruins of the ancient Buddhist temple of Angkor Watt (originally Hindu) in Cambodia, photo by Bjørn Christian Tørrissen - similar in size but of course was built with the technology of twelfth century Cambodia.

MEGA PROJECTS - LHC, IRRIGATION PROJECTS, GREAT WALL OF CHINA, ARTIFICIAL ISLANDS, HIGHWAY PROJECTS

Another modern example is the Large Hadron Collider. This cost around nine billion dollars. So you could build more than eleven of these for the cost of the ISS.

Some mega projects have cost even more, for instance long distance canals and irrigation projects, or some of the modern hydroelectric dams. As an example, the Three Gorges Dam in China cost around 28 billion dollars, so you could complete around three and a half large hydroelectric mega projects for the price of the ISS.

The Khazar Islands project is expected to cost $100 billion, so the same as the ISS. The US Interstate Highway System cost an estimated $425 billion (in 2006 dollars).

The Great Wall of China may well have cost more than the ISS. It employed probably over a million people at times, and took centuries to build which would seem likely to raise its total cost to hundreds of billions (a million people for three years would be equivalent to around a hundred billion dollars cost).

However, perhaps that is rather stretching the idea of a "single item "

STONEHENGE

There's an estimate here of the total hours for building Stonehenge - about 675,000 hours. THE COST OF BUILDING THE STONEHENGE COMPLEX

So - taking 34,000 as average annual salary for a labourer in the US, and 2,080 hours a year, that's 34,000*675,000/2080 or about eleven million dollars.

That's the equivalent of 325 people working full time for a year. You might be a little surprised that so few people could build Stonehenge - but they had sleds and other quite sophisticated equipment. In practice this work was spread over many generations of course.



Stonehenge (credit Diego Delsa) - eleven million dollars worth of labour, could build 9,000 using neolithic methods

So we could build 9,000 Stonehenge monuments, using neolithic methods, for the cost of the ISS.

THE CLAIM SEEMS REASONABLE

So, the claim seems reasonable to me, as best we can guess. It's amazing how much a few hundred people, working for a year, can accomplish, so probably many of the other ancient monuments would come in at similar costs to Stonehenge, medieval cathedrals, or the pyramids.

And - with the difference that the ISS has a short lifetime. There won't be any future tourists visiting the ISS a thousand years from now, because it will be de-orbited and the whole thing burn up in the upper atmosphere some time in the next couple of decades. Same for all our space stations. Space is a harsh environment and after a few decades, the modules are no longer worth maintaining any more, at least with present day construction methods.





The ISS is one of the brightest objects in the sky, brighter than Venus.



It is also possibly the most expensive single artifact ever built by humans. And it's got a short lifetime, and is nearing the end of its lifetime.



Within one or two decades, most of its modules will be past their useful design lifetime and (after removing anything that is still useful in space), it will need to be de-orbited and most will burn up in the atmosphere. What is left will target a remote place in an ocean, such as the Pacific, graveyard of many spacecraft.





Spacecraft cemetery in the south Pacific - final resting place for fragments of 161 sunken spaceships including MIR



It could be boosted to a higher orbit instead, to a parking orbit as a "museum piece" but this would be a major expense, for something that seems likely to have no further practical use. And we haven't yet reach the level of technology needed to use materials in our spacecraft in space for other purposes.

However there is another way of looking at it.

ANOTHER WAY OF LOOKING AT IT - COMPARISON WITH TOTAL ECONOMY OF THE SOCIETY

If instead we compare these prices with the total economy and the number of humans now on the Earth, the ISS is not such a huge cost.

Back when they built Stonehenge for instance, this may have taken much of the effort of an entire community for generations. So - as a percentage of their economy, it might well have been higher, even if adjusted to US dollars, e.g. counting the cost of the number of workman hours they put in, it might not cost that much.

I think would be hard for anyone to answer that, it would involve estimating their total economy - and what size of a region of England was involved in building Stonehenge. We can do the calculation for the ISS anyway, at least in a rough way.

COMPARISON WITH GROSS WORLD PRODUCT

The Gross world product is US $87.25 trillion in purchasing power parity.

Compared with that, the ISS cost is 0.17% of the yearly gross world product - but spread out over many years.

Equivalent of one person out of every ten thousand throughout the world working on it for the last seventeen years, if I've got this right. It is a pretty major project for the world to undertake, seen that way. But probably not such a major effort as Stonehenge was for its community.

Also given that it was built by the richest nations, with higher salaries than most of the world population - the ESA estimated that the lifetime cost of its contribution to the ISS was about one Euro per person, or the price of one cup of coffee in a coffee shop, by each person living in the EU. That is a single cup of coffee to pay for the entire cost of the ESA contribution to the ISS throughout its lifetime, not one coffee per year.



The ESA estimates that the cost of its contribution to the ISS is equivalent to the price of one cup of coffee in a coffee shop per person - that is a single cup to cover the entire lifetime cost of the ESA contribution to the ISS

So from that point of view it doesn't seem like such a major cost.

The USA made a far larger per capita contribution. With a population of 318.9 million, it spent the equivalent of $72.4 billion in 2010 dollars, so that's $227 per person spent on the ISS. Still that may not seem a huge contribution for a nation that is especially keen on humans in space, for a 30 year project, so a little under $8 per person per year.

I am in two minds about the ISS myself. Depends on whether I wear a "science hat" or a "political hat" :).

SCIENCE VALUE OF THE ISS

I don't think those costs can be justified by the research alone, because we could have built it as a telerobotic facility operated from the ground, and done nearly all the same research for far less cost except the research into human effects of weightlessness. I don't know of any comparison study, but without the need to send humans there every few months, wouldn't be surprised if that would have cost an order of magnitude less.

WOULD BUILD IT DIFFERENTLY WITH DIFFERENT PRIORITIES FOR HUMAN FACTORS RESEARCH

Yes, it gives us experience in humans living in space, but it's not a research priority to find out how best to sustain humans in closed systems for long duration spaceflights either. It would be built differently if its primary purpose was to prepare for interplanetary flights or a return to the Moon.

So it seems a bit of one thing and a bit of another- mainly a zero gravity lab, but operated by humans with some human factors research, but not prioritized for that either.

If it was prioritized for human factors research there would be far more focus on such things as developing closed systems, growing food in space, generating oxygen from algae, and artificial gravity research.

AND SURELY ASTRONAUTS ARE NOT THE MOST COST EFFECTIVE WAY TO DO THE ZERO GRAVITY RESEARCH

And then, using humans for the other zero gravity research is surely not the most cost efficient way of doing that research.

If your main aim was to build a zero gravity laboratory in space, and if you didn't have the (very natural) political requirement that you have to have astronauts on board 24/7 and give countries involved as many as possible opportunities to send astronauts there - without that requirement - I don't think you would build the ISS.

I think that - probably - you'd build a lab that can be operated from the ground, with humans visiting it from time to time for maintenance and to set up experiments etc.

At any rate, you'd have seriously explored that possibility at least and done careful cost comparisons to see whether and for how long you needed humans in space to keep it all running, and made it so you can run it from the ground as much as possible, because, obviously, man hours in space are expensive.

It costs the equivalent of an astronaut's weight in gold to send them to space for one week, at least going by the amount the Russians charge tourists on the ISS. How much does it cost to ferry an astronaut to the International Space Station? Or if you work the other way from the estimated total cost of the ISS, then it's about $7.5 million a day per astronaut - more or less the same ballpark (a little less).



Native gold nugget from Venezuela, photo by Rob Lavinsky

It costs, very roughly, the value of an astronaut's weight in gold to keep an astronaut on the ISS for one week. If your main aim was to run a zero gravity lab in space, you'd find a way to make sure the astronauts travel to the ISS only occasionally, and operate the experiments from the ground as far as possible.

If you had to justify the ISS as a science project, competing for research grants with other big budget science projects - I think you'd have a lot of explaining to do, to show why you want to run it this way, rather than telerobotically.

HUMAN VALUE WITH SCIENCE AS EXCELLENT "ADD ON"

But on the other hand it is hard to assess how much value it has had in terms of international co-operation, and the astronauts view on the Earth from space, and other intangible effects. And that wasn't their mandate, to build either a human factors research station, or the least cost way to make a zero gravity lab.

I think it is fair to say it is more like Apollo, politics led, with objective to have a permanent human presence in space and involve astronauts from all the participating parties - then adding as much good science to it as one can.

And given what it is - it does do a lot of excellent scientific research.



If it has as much as saved us from a single war also, even a minor war, through co-operation in space, then it is well worth it.

COMPARISONS WITH OTHER WAYS OF USING THE MONEY

And the countries involved spend far far more on their military programs than they do on the ISS. In 2015, the US alone will spend around 600 billion on defence, four times as much as the whole world has spent on the ISS over its entire lifetime. So if you think of it as funding that might otherwise have gone on defence, it's not a huge sum.

If you think of it as money that could have been used for planetary exploration, it's enough for an extra flagship class $5 billion extra mission every year for 30 years (normally NASA only do one of those every decade). We could have highly capable robotic spacecraft around every planet in the solar system and on the Moon and many rovers on planetary surfaces if we'd spent this money on robotic exploration. And it is enough to do a hundred and fifty $1 billion surveys of all the world's oceans.

Then if you think of it as used for alleviating poverty, providing clean water for the world, etc, well it is a big sum. It is enough to fund three years of the five year project to bring clean water and sanitation to all.

WHY NOT BOTH?

However it's not either / or anyway. There is no reason at all why we can't have both an international space station if we so wish, and planetary exploration, and do a complete survey of all the Earth's oceans, and clean water for all as well, and achieve many other things. (Suppose that the US and Europe clubbed together, that's a billion people so they can achieve a $1 billion dollar project such as surveying all the world's oceans with $1 each, or a $250 billion dollar project to bring clean water to all over five years, with $50 spend per capita per year).

So, I don't think myself that the best way to achieve humanitarian goals is to cut back on other things that people also find inspiring. They are like the "soft targets" because people talk about them and they are very obvious targets precisely because they are inspiring.

As a planet we are actually quite wealthy and can afford to do such things. Our future I hope will be a world where every child has the same expectation of a life without poverty, a healthy life and a decent education. It is something that we have almost within reach, and no real reason why we can't get there. The UN continues to set targets of humanitarian goals, one decade after another (here are some of its goals for 2030), and - not often publicized so much, but these goals are actually being met, also (some of its recently achieved goals from previous targets).

But hopefully this will also be a future where we will continue to do things that we find inspiring on many levels, whatever those happen to be. Whether they are cathedrals, or temples, or pyramids, or megaliths, or space stations, or whatever it is that inspires us and carries our aspirations forward in the future.

FUTURE OF SPACE STATIONS - DO THEY ALL HAVE TO BE THESE 150 BILLION DOLLAR PROJECTS?

First, launch costs are going down. With SLS when it is ready, if that works out, we could launch the total mass of the ISS with just four launches (up to 130 ton payload, ISS mass about 420 tons).

Inflatable habitats such as the Bigelow habitats also have potential to reduce costs enormously. The BA 330 will have 330 cubic meters of internal volume, for only 1 ton of extra mass, 20 tons instead of the 19 for Tranquility which has a pressurized volume of 70 cubic meters. So nearly five times as much volume for almost the same mass.



Bigelow BA330 inflatable habitat - will be 330 cubic meters, nearly five times the pressurized volume of Tranquility for almost identical total mass, 20 tons instead of 19

Then, all our space stations to date - I think that ISS, MIR, Skylab etc - are manly focused on zero gravity research.

Important though this zero gravity research undoubtedly is, still, it remains a fact that in all this time we haven't had any experiments in generating artificial gravity in space and its effect on humans. Just to get the first ever data points from space could be well worth doing to prove - or disprove, or shed new light on the various attempts at predicting the effect of artificial gravity on humans from ground based experiments.

Indeed we have done hardly any research at all in low gravity either. Could you grow plants in a greenhouse on the Moon, and how would they do?

Also, could a space station in future try to generate some of their oxygen from green algae, to test to see if this is possible in space conditions? Or try growing plants in space in a big way, not just a few lettuces? In ground experiments, crew were able to generate all their oxygen and most of their food from three modules each of 79 cubic meters.

Will we get to test this in space any time soon?

I think that in the future we may see more research of this nature.

If we ever send humans back to the Moon or to interplanetary space for years on end rather than the few days of the Apollo missions we need answers to these questions. And if you can generate all the oxygen inside a spacestation, and scrub the CO2 using plants, and keep humans healthy using artificial gravity- this also has potential to reduce the number of supply missions to a space station.

Maybe for our next space station we can reduce the cost further if we make some of the food and all the oxygen in orbit? And maybe if we have astronauts under artificial gravity, they won't need to spend two hours each day of their precious time in space exercising, just to keep at the same health levels as a bed bound patient on the Earth (and possibly not even that).

I've done many posts about artificial gravity here. But not yet done all that much on growing plants in space. So, I'm going to do another post about that, soon, on "Why doesn't the ISS generate all its oxygen from plants and use them to scrub its CO2".

(Much of this originates in my answer to a question on Quora: is the ISS the most expensive single human artifact ever, after adjusting for inflation?)

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COULD WE SAVE THE ISS?

I'm sure they'd like to. The problem is - how do you justify the cost?

The planned de-orbit would involve two progress vehicles attached to the ISS to de-orbit it. The progress vehicles would just be used to control where it lands. The actual de-orbiting happens through atmospheric drag.

To boost it to a higher orbit would need a lot more than two progress vehicles. They can only manage a relatively feeble a few meters per second adjustment in the trajectory of the entire 419 tons of the ISS. Typically it boosts its orbit by a couple of meters per second per month.

I once had a go at trying to figure out how many Progress vehicles you'd need to boost the ISS to a lunar orbit, or say to Lunar L1, it came out at 143 progress launches, loaded with fuel to capacity, including fuel as cargo also. That was a very rough calculation, but it gives an idea. Also the Soyuz has a limit, so you'd need a relay of one Soyuz fueling another to get fuel supplied to a high enough point to continue boosting it.

So, it seems likely to be a multi-billion dollar project or more, to boost it to a higher orbit to save it.

It would be different if you had some future practical use for it. If so would be some requirement that doesn't have people on board 24/7 since in higher orbits it would be exposed to much higher radiation levels, as well as being hard for humans to get to with current technology.

There is this 2010 idea, to detach one of the newest nodes of the ISS and send that on a deep space mission as a spaceship after refurbishment

You could also just boost it to the highest orbit you can get it to with a couple of Progress launches - and commit yourself to sending a couple of Progress up to the ISS every few years, just to keep boosting it to keep it in a higher orbit, if you were willing to take on a recurring expense like that to maintain it as a "museum".

The Russians have plans to re-use some of the modules for their future OSPEK space station.

SPOT THE ISS FOR YOURSELF

You can see the current position of the ISS on a map here: Current position of the ISS. Or on a global map here: ISS tracker

You can sign up at the NASA website to get email alerts whenever it is visible from your location.

You can also download apps for iOS or Android that alert you if it is visible.

And, you can also use the Heavens Above website which tracks the ISS and many other satellites. Enter your location, and then you can look for future (or past) predictions for the ISS for any date you like, with full details including the direction, altitude, exact time, even a sky chart that shows you the exact track across the sky as seen from your location.

If you've ever seen a satellite - well it is like that but much much brighter. It looks as bright as a plane flying over - but pure white, no coloured lights and of course, no sound. Moves smoothly and steadily, quite fast. And you may spot it "blink out" as it passes into the Earth's shadow - because then it is no longer illuminated by the sun.

COMMENTS SECTION BELOW

Do you have any other favourite examples to compare costs with the ISS? Do say in the comments, or share any other ideas or thoughts on this. Also please don't hesitate to say in the comments if you spot any typos, errors or confusions in this article. Thanks!

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