Epistemic status: Uncertain, shooting from the hip a little with no expertise in this area and only a couple of hours research done. I might well have missed something obvious, in which case I’ll revise or even take the post down.
Money Waste is Everywhere
Here in Northern Uganda where poverty abounds, many expenditures feel wasteful. Last night I had a great time at the fanciest restaurant in town with friends but felt a pang of guilt about my $7 meal. Enough of a pang to avoid telling my wife after I came home.
A bigger scale waste in these parts is the partial closure of the main bridge across the river Nile, because the bridge has apparently degraded and become hazardous. Vehicles larger than a minivan now can’t cross, which has raised the price of public transport by 50% and trucks now have a 3 hour detour. Besides these direct costs, this closure increases the cost of fuel and commodities in Northern Uganda. By my loose, conservative BOTEC the closure costs $10,000 every day (1.2 million dollars in 4 months so far) which Ugandans now can’t spend on education and healthcare, while likely causing more crashes due to increasingly tired drivers who now use worse roads. The detour itself may have already cost more lives than would be lost if the bridge does collapse and kills a few people.[1]
But there are far bigger wastes of money on this good earth.
A Billion Dollars to bring down a space station?
Space X have secured an 843 million dollar contract[2] to build the boringly named “U.S. De-Orbit vehicle” (why not "Sky Shepherd")[3], which in 2031 will safely guide the decommissioned International Space Station (ISS) into the Pacific Ocean. This all sounded pretty cool until I thought… is this worth it?.
No human has ever been definitively killed by an object falling from space, although there have been a couple of close calls with larger asteroids injuring many while Open Asteroid Impact could be a game changer here in future. This one time though, a wee piece of space junk did hit Lottie Williams in the shoulder and she took it home as a memento. I’m jealous.
According to a great Nature article “Unnecessary risks created by uncontrolled rocket reentries”, over the last 30 years over 1,000 space bodies have fallen to earth in uncontrolled re-entries and never killed anyone. The closest call might be a Chinese rocket in 2020 which damaged a house in the Ivory Coast. The article predicts a 10% chance of a fatal space junk accident in the next 10 years – far from zero and worth considering, but unlikely to be the next EA cause area. This low risk makes sense given that only 3% of the globe are urban areas and under 1% actually contain human homes[4]– most stuff falls down where there ain’t people. Also the bulk of falling spacecraft burns up before hitting the ground.
In contrast a million people die from car crashes every year,[5] and each of us has about a 1 in 100 chance of dying that way.
Although the ISS is the biggest ever at 450 tons, we do have priors. Two 100 ton uncontrolled re-entries (Skylab and tragically the Columbia) crashed to earth without issue. So what actually is the risk if the ISS was left to crash uncontrolled? The U.S. Government requires controlled re-entry for anything that poses over a 1 in 10,000 risk to human life so this risk must be higher. NASA doesn't give us their risk estimate but only state “The ISS requires a controlled re-entry because it is very large, and uncontrolled re-entry would result in very large pieces of debris with a large debris footprint, posing a significant risk to the public worldwide” [6].
I hesitate to even guesstimate the risk to human life at the ISS falling, but I’ll throw out a number. Given we’ve had over 1,000 (albeit smaller) spacecrafts fall without a death yet, and the Nature paper estimates a 10% chance of death from the 600 spacecraft which will fall over the next 10 years, I’d be hard pressed to estimate anything higher than between a 1 in 100 and 1 in 1,000 chance of a deadly crash, although multiple casualties would be possible.
100 Billion per life saved?
That would mean that the projected cost per life saved might be over 100 billion dollars here – I’m not pitching this safety project to GiveWell. This could make the controlled descent of the ISS one of the largest, least cost-effective safety initiatives of our time.
Yes NASA has other considerations, like getting sued for breaching government safety standards, and the PR disaster as millions of us sit at home in 2031 glued to our screens, irrationally worrying more about the ISS hitting our home than we are getting in their car the next day - but these hardly seem billion dollar concerns. NASA might also be keen to maintain their good reputation as a steward and leader of space governance, as they try and keep the moral high ground while working on other important agendas like reducing space junk. (Thanks @David T)
Although stopping this government expenditure seems intractable at this point, I think its helpful to consider waste on all scales from time to time, especially when its our own tax money paying the bill.
have no expertise at all in this field so I might just be missing something obvious, so feel free to correct and fire away .
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Karuma Bridge is only 70 meters long with only 1 - 3 vehicles crossing at any one time.
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https://www.nasa.gov/news-release/nasa-selects-international-space-station-us-deorbit-vehicle/
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Even ChatGPT did better with “Sky Shepherd”, “Descender X” and “Stellar Dropper"
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https://www.researchgate.net/publication/261718817_How_much_of_the_world's_land_has_been_urbanized_really_A_hierarchical_framework_for_avoiding_confusion
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https://www.who.int/news-room/fact-sheets/detail/road-traffic-injuries#:~:text=Approximately%201.19%20million%20people%20die,adults%20aged%205%E2%80%9329%20years.
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https://www.nasa.gov/news-release/nasa-selects-international-space-station-us-deorbit-vehicle/
Needless to say, NASA does not use EA math in its budgeting ;-)
The world's major space agencies abandoning the biggest thing we ever put into space in an uncontrolled deorbit is a politically untenable option (and the project represnts only around a third of the estimated $3bn annual budget to keep the ISS operational, although there's an argument this spend has more ROI...). That's even more the case against a backdrop of increasing calls for more regulation around everyone else's launches and orbits and deorbits to prevent collisions in space[1]
The potential risk to human life of uncontrolled ISS reentry therefore isn't the only factor in the decision and probably not even the main one, though I don't think the deorbiting of generally orders of magnitude smaller stuff gives much of a guide to the magnitude of that risk.[2] (There are of course also other arguments against spending money on this project, such as the desirability of maintaining the ISS, the possibility of raising it to a graveyard orbit for future reuse/recycling instead of destroying it; and other arguments in favour such as the likelihood at least some of SpaceX's R&D can be deployed to more productive projects in future). Space agencies usually aren't especially rigorous in analysing cost effectiveness anyway, but cost-per-life saved is a pretty minor factor in why such contracts are awarded. Space funding is industrial policy targeting notionally large medium term returns from technology, not evidence-based philanthropy trying to find the most cost effective way to remedy problems.
this potentially compounds, with each debris impact creating more orbital debris, with the theoretical possibility of rendering some orbits unusable in future. Avoiding this scenario might still seem wasteful from the point of view of a Ugandan farmer whose neighbourhood could be fed for years on the research budgets being devoted to maintaining congestion-free orbits, but rather a lot of the developed world depends on access to satellite technology and I suspect even some NGOs in Uganda make some use of GPS and satcomms.
but that risk is probably still low, assuming even with it rentering via gradual orbital decay, operators would still have sufficient ability to control reentry using onboard thrusters to direct it to scatter it's debris over thousands of kms that's mostly ocean or sparsely populated, as with Skylab...
Thanks so much David nice one!
I love your comment about it being "politically " untenable you might be right on the money there - even though of course there's nothing about that in NASA discourse
The reason I wrote this post was because at least in the public facing materials I read, public human safety on earth was NASA's only reason for doing a controlled vs random re-entry. Of course you could well be right that other considerations are more important than public safety that they're not talking about but that's all they list on their site - the full blurb is here below. They don't mention the possibility of uncontrolled re-entry causing debris, nor the possibility of a collision on the way down. I assumed (like you said) this was because they would still have relative control of the re-entry using the boosters on the station.
"The U.S. Government specifies that re-entering spacecraft must meet or exceed a 1-in-10,000 likelihood of public risk due to debris. An inability to meet this specification requires the spacecraft to conduct a controlled deorbit, which is a standard industry practice for spacecraft that exceed the U.S. Government’s safe re-entry requirements unless the spacecraft operates near a disposal orbit, such as a geosynchronous orbit. An uncontrolled deorbit occurs when a spacecraft enters the atmosphere without navigational or propulsive control and is only acceptable when the debris impact risk to the public is small (i.e., a small spacecraft or the structure breaks into small pieces and has a small debris footprint). The International Space Station requires a controlled re-entry because it is very large, and uncontrolled re-entry would result in very large pieces of debris with a large debris footprint, posing a significant risk to the public worldwide. Ensuring the space station is well maintained continues to be the safest operational approach while also planning for deorbit at the space station’s end of life.
The use of existing space station propulsion systems, such as the Roscosmos Progress vehicles, would provide an alternative to an uncontrolled re-entry prior to the arrival of the U.S. Deorbit Vehicle (USDV). However, these systems do not provide sufficient margin to lower the public risk to an acceptable level. The USDV will provide this margin to lower the public risk to U.S. Government standards. "
Read more on the agency’s International Space Station Deorbit Analysis Summary white paper. "
I completely agree that keeping low orbit clear of debris is critcally important and probably worth far more than a few billion dollars, but they only discussed that being an issue if either the ISS was destroyed at its current orbit, and as also being a big risk also if they tried to elevate it to a higher orbit.
Just to clarify on the orbital debris problem: it's not just the risk of the ISS specifically hitting things on the way down (which is non-zero but at the same time not that likely: the ISS is too big to overlook and will move in a reasonably predictable manner so things will generally adjust their orbits in advance to move out the way, and most of them have higher orbits anyway). It's also that when operators of thousands of other satellites[1]- from Starlink to university cubesats - are being advised/required to have specific end-of-life deorbiting strategies to avoid creating more orbital debris, all of which cost them money in terms of additional man hours and launch mass, and lots of research dollars are being spent on addressing the problem of orbital debris, the world's major space agencies can hardly state their end of life strategy for the ISS is as long as everyone else gets out the way and then when it breaks apart in the upper atmosphere the pieces land somewhere like Australia or the sea it probably won't do any real harm. It's really bad politics to demand everyone else is a responsible citizen whilst shrugging your shoulders about the fate of your flagship. And nearly all the alternatives - especially those discussed in the white paper - would cost more.
And yes, in the scope of the operations of the ISS $843m isn't even that big a number, which I realise may seem obscene in a country where that sum of money would buy the entire population a couple of malaria nets
(FWIW I still think you can [i] make a good case that the project is premature, the wrong approach or poor value for money and [ii] make a good case that SpaceX has done unusually well in turning pork-barrel projects into useful, value-for-money services and may do so again despite the project being premature, the wrong approach and/or poor value for money)
most of which were launched in the past few years, which is why history isn't a reliable guide...
I don't think bringing the ISS down in a controlled way is because of the risk that it might hit someone on earth, or because of "the PR disaster" of us "irrationally worrying more about the ISS hitting our home than we are getting in their car the next day".
Space debris is a potentially material issue.
The geopolitics of space debris gets complicated.
I haven't done a cost-effectiveness analysis to justify whether $1bn is a good use of that money, but I think it's more valuable than this article seems to suggest.
I'm deeply concerned about space debris, but I don't think it alone could justify this project. A 'controlled' descent sounds like it's about targeting a specific landing spot - an 'uncontrolled' descent could still lower the ISS sufficiently fast as to minimise its chance of hitting orbiting debris (it probably lowers it faster!).
Also the ISS is also already well within Earth's atmosphere, and the lower it gets, the shorter the life of debris hitting it would be due to atmospheric resistance, and it would presumably be relatively easy to control it from hitting anything near the start of its descent, when you can choose when to start the process and only run serious risk as it started to lose control 0 in the lower, thicker atmosphere.
The ISS itself isn't particularly likely to create space debris (its orbit is already lower than major constellations and anything with thrusters is going to move out the way, and if it breaks up as it hits the upper atmosphere the pieces will rain over earth rather than remain in orbit). But tens of thousands of other satellites being launched this decade have plenty of potential to create space debris, space is a commons and space law is by international treaty with lots of blank spaces (unlike, for example, the heavily-regulated airspace).
If the deorbiting strategy for the ISS is "we decided that to save a third of the annual budget we usually put in, we'd do a reentry with limited control from its onboard thrusters because only a few islands might get hit, and in fact even though we missed the target we didn't hurt anything except an abandoned chicken shed", or "we left it to Roscosmos to figure out"[1] nobody is going to listen to NASA's guidelines for a safer space (not even Congress). Especially since all the precautions everyone else might need to take will cost them significant money.
there are other political considerations to leaving it to Roscosmos to figure out of course, even though they're hardly likely to target California with it, and tech developed to deorbit the ISS isn't going to be more useful as an antisatellite weapon than dozens of existing civil projects to create tugs for deorbiting and servicing defunct smaller satellites)
I agree with all this. I was just commenting on the issue of debris specifically.
Thanks David yes I think I understand this now!
I understand why the international community doesn't see it this way because they meld the two together, but I would distinguish between safe space, and safe people on earth. Space governance vs. earth governance
You've said that space is a commons, and space law is international treaty - what does a re-entry have to do with this that doesn't affect space? From my perspective safety of people on earth has nothing much to do with the governance and safety of space, so shouldn't necessarily be part of the political discussion about responsible space debris.
But 100% I can see how those 2 things get connected politically, like "if you are willing to be loose with your huge space station, why should we pay more to stop our satellites becoming space debris?" Even though one of those things is about Earth governance and the other space.
Ultimately the safety of the space domain and safety on earth from space debris are linked by both overlapping technologies for monitoring and mitigation and the overlapping principle that entities ought to take responsibility for what they put into space. And from that perspective it would be pretty hard to lecture foreign universities on why they should spend a few grand on safely deorbiting their Cubesat to mitigate a very small risk of hitting other satellites whilst being the entity that decided to abdicate responsibility for safely deorbiting the ISS to mitigate a very small risk of hitting a densely populated urban area - to save a lot more money but still only about 4 months of ISS budget.
Ultimately they're optimising for technological potential rather than saving lives, and the budget for this is far more closely linked to debates like "but we can't trust the Russians to manage the deorbiting process, can we", "does it have commercialization potential" and "could it be turned into an ASAT weapon" than "would it save more lives than the debris could possibly threaten if we bought $843m worth of medicine instead?"
Thanks David this is excellent. Have added a sentence (crediting you) in the main body which hopefully reflects your point here.
Is interesting that many people are taking about space debris when NASA don't mention that as a consideration in the mode of coming down. Do you have a link which states that add an issue?
Sanjay's link about Kessler Syndrome above describes the problem. If you mean about the ISS specifically, I think it's just an instance of the general concern.
I get that it's a big problem in general, but NASA haven't discussed it as a Factor in controlled vs. uncontrolled reentry.
It seems like it might not be, for the reasons I suggested or others?
Oh I think I get it now, I was confused by "don't think it alone could justify this project" because from what I can see it isn't a consideration at all
Right, sorry. Yeah, I have no view on whether it's a consideration at all, just that it seems unlikely to be a primary one from my rudimentary understanding of the issue.
Thanks Sanjay - I'm going off NASA's public facing materials, where they don't mention space debris as a potential consideration in controlled vs. Uncontrolled descent. They mention that as a reason why they don't destroy it in situ or try and take the ISS to higher orbit.
I completely agree, if space debris was a serious consideration then it would be a while different equation.
Good analysis, thanks for writing this up! It does seem that in general our political/regulatory system has little to no sensitivity to the dollar cost of fulfilling requirements and avoiding identifiable but small harms.
I like this discussion a lot thank you.
Is it about safety? I imagine it's important to future generations as a significant artefact of history. A thousand years from now if we figure out how to make it there, probably people will treat the ISS as a kind of gateway / shrine / pilgrimage if they're hella nerdy and feel like getting off planet matters. Totally making this up.
I do feel like politics and PR have played a big part in the space race since the start, nature of the beast.
Possibly it's important for another longterm reason. If SpaceX is going to play the role of ferryman to future space exploring civilizations like it claims to want to do, they are essentially setting the standard.
Other private space companies are all watching, even ones that don't exist yet (will look back through history). The choices that get made aren't just important here for their real and current impact, but potentially also for setting the precident for future decision makers. If we act with (at least visible) integrity in these choices then what impact might that have on the court of public opinion for how we expect companies to operate?
quick note: Open Asteroid Impact, or OpenAI, is a joke about Open Artificial Intelligence, and is not a real company.