Global warming can now be reversed
by shade from moon dust placed in space
By David Chaum
Recently-demonstrated technologies, when combined in the novel way detailed here, can allow us to reset global temperatures to pre-industrial levels in a few years. And this can be done without harmful effects on the environment—since the technologies operate literally nearly a million miles from Earth. Because the solution can be applied differently per season and region, all regions of the planet should be asked for approval in advance. A global referendum, using proven remote-voting technology, can demonstrate majority popular support across regions. This referendum can also call on governments to commit to fund it, at least once a global contest proposed here tests all the details in space and a second referendum gives the final approval.
Within the last year, aerospace has proven out the main technologies needed for AstroCool, as part of a push to realize a materials and energy economy in near-Earth space. But already fifty years ago, moon dust was brought back by Apollos 11, 12, and 17, establishing it as a plentiful and excellent light blocker.1 Placing enough of this dust near the gravitational balance point between Earth and sun, called “L1,”2 can cool the Earth by blocking 2% of sunlight.3 In 2022, SpinLaunch’s NASA mission reached a milestone on the path to lunar escape velocity.4 So sending moon dust to L1 is within reach, especially since it is so much easier to launch from the moon: the moon’s lack of an atmosphere obviates the need for the costly vacuum chamber, and its one-sixth Earth gravity substantially reduces the exit velocity needed. Also in 2022, NASA’s DART mission demonstrated a remote-controlled spacecraft rendezvousing with and moving an asteroid, thereby establishing the feasibility of intercepting packaged dust sent from the moon and then positioning the dust at L1.5
The global referendum can be performed using technology that has already been tested. It is called “sample voting” since it uses a survey-sized sample of the population. If there is ample margin, it irrefutably proves majority support.6 Voters are selected at random and their votes tallied, using cryptographic techniques whose integrity can be proven mathematically. Also important is that the votes are secret—nobody can see how an individual voted, not even if that voter wants to show them, such as in vote selling. Because all the data is published online, voters can readily verify their own contributions and the whole process can be verified by open-source software.
The other key ingredient needed, besides technology and commitment, is a structure that incentivizes and coordinates the most capable groups to help meet this grand challenge. Proposed here is a competition structure that leverages the strength of the worldwide aerospace industry to prove out the most viable route to getting the job done. The competition structure, detailed in Appendix I, provides state-of-the-art fairness and openness, while deploying proven aerospace management techniques. It also provides for pooling of software and patents and supports participation by small innovators and the interested public.
Beyond civilization-saving cooling, AstroCool may well end up forming the cornerstone of the widely envisioned initial space-based economy, termed Cislunar.39 This provides huge further incentives for participants in the competition. It also makes AstroCool not only what we can and must do, but attractive as an investment because of its tremendous upside.
The infrastructure needed for AstroCool is enough to dramatically reduce the fundamental costs of transport, lunar operations, and near-earth space operations.40 The same spin launchers and launch velocity can also send payloads back to Earth. And the market for space-based tasks once the spacecraft are free of earth’s gravity, such as shepherding bags of dust, can help cover the relatively higher launch costs. Moon-based operations can not only employ dust as construction material, but prospect for and extract valuable metals and minerals. Also, the hundreds of billions of gallons of surface water frozen at lunar poles can be converted to fuel.
The scale of AstroCool is comparable to other technical activities today. Its setup can be expected to be less than the rapidly-growing current rate of a thousand launches per year. The area that needs to be covered by dust is roughly that of Brazil,22 but because it is spread so thin, the amount of dust is similar to the amount of concrete used for the Three Gorges Dam, or the rate of a few typical fire hoses. Compare this to fossil-fuel extraction today: fifty thousand new oil wells drilled per year, trillions of pounds of tar sands extracted each year, plus coal mining continuing to approach ten trillion pounds annually. It’s hard to nail down the exact parameters of AstroCool at this stage, but its scale can best be understood as an economy-enabling feature rather than as a serious obstacle.
The proposal here for reversing global warming is game-changing. It reduces the average global temperature directly, and there are only two known ways to accomplish such direct cooling. One is by introducing particulates into the atmosphere or on the Earth’s surface, which is generally very poorly regarded, not least because of potential damage to the environment. The other approach is space-based shading like that described here. Previous proposals for space-based shading were, even when not aimed at only a partial solution, arguably science-fiction-like and barely affordable. Asteroid dust at L1 was proposed a decade ago by one group of authors;7 however, they suggested no practical way to obtain it.
It would be extremely expensive—in human life, in resources that could otherwise benefit humanity, and in difficult-to-reverse accumulating damage—to delay addressing this global grand challenge while debating even the most legitimate of concerns. As argued below, the only rational thing to do is start a no-cost-to-governments and risk-free competition in parallel with discussion of concerns. Addressing accumulated carbon in the atmosphere is planned as a final phase of AstroCool, once a solution to the immediate danger is launched.
The first section below covers technological feasibility; the next section attempts to address the full range of other potential concerns; and a final section tackles the issue of timing.
TECHNOLOGICAL FEASIBILITY
Compared to accomplished space missions, such as manned moon visits or space stations, AstroCool has significant advantages in terms of technological feasibility. For one thing, it can be unmanned, yet is not too far to be remotely controlled from Earth. For another, the level of overall technology has advanced considerably since these earlier missions. Moreover, the competition structure is unprecedentedly open and flexible. Not only does it allow pooling of technology but it lets contributors focus on particular parts of the system initially, then later partner in stages to provide a complete deployment. And the competition excludes no approach to getting dust to where needed at L1.
The transport technologies critical for the proposal—launch from the moon and positioning at L1— essentially have succeeded in NASA missions, as already mentioned above. However, there are differences in the environment of deployment and in the details of use that ultimately require careful consideration.
In the 2022 SpinLaunch mission for NASA, a 30-meter diameter vertical centrifuge in a vacuum chamber, launched 450 pounds into a sub-orbital trajectory. According to the company, the next target is a 90-meter centrifuge thirty degrees from the horizontal that would launch 10 metric tons at 5,000 miles per hour.8 This is just a few percent less than the speed needed to launch from the moon to L1 (from earth it would be five times greater). The centrifuge bearing, like that of a CD or record player platter, is only attached on one side, so on the moon it can simply be anchored, such as to a boulder or outcropping, without requiring any additional support structure to be transported from Earth. A shorter arm could probably be used to launch dust, as that mainly increases the g-forces on the payload; but dust can endure much higher forces than the type of payloads the company is targeting. A 40-meter arm divided into two sections could fit as the payload of launch vehicles, such as the SpaceX Starship.9 Superconducting tapes, now used commercially for magnetics,10 allow motors one third the size with almost no heat loss, making spin-down generation also efficient.*
* A launch device modeled after the continuous operation of so-called “centrifugal machine guns” could replace many single-load launchers.
The other major infrastructure of AstroCool is the fleet of spacecraft at L1. The size of the fleet needed depends on the tradeoff to be made between dust package size and frequency of delivery as well as on accuracy of launch.† Since the interceptor spacecraft would most likely be powered by solar or nuclear, as would the launch centrifuge motors, the main consumable needed on the moon is bags for dust. Supply launches for additional bags, along with equipment maintenance, are anticipated to be the most significant operational costs.
† If dust or dust packets could be dispursed by in-built explosives or by the dissolution of dust adhesion additives, the number and/or size of spacecraft needed could be greatly reduced.
Dust is at the heart of AstroCool’s two main supporting technologies—filtering dust and situating de-agglomerated dust in space. The former has been the subject of NASA-backed tests; the latter still requires extrapolation from Earth-based industrial practice. Because the competition structure allows in effect separate initial competitions between multiple approaches for each of these two supporting technologies, and each has many solution approaches, it’s likely that there will ultimately be good options to select between.
The moon is almost entirely coated with a layer of dust-containing regolith that is estimated to be from five to ten meters thick.11 Collecting, filtering, and packaging dust would be done by machines remote-controlled from Earth. So gathering, filtering, and packaging dust is relatively straightforward.12 The NASA “In-Situ Resource Utilization” project13 supported research on how best to separate moon dust by particle size, partly aimed at mining valuable minerals and as a construction material for moon bases. One solution demonstrated in vacuum was a solid-state electrostatic regolith dust sorter.14 Bags widely used for about a ton of sand or other dry flowable products are called “flexible intermediate bulk containers” and are usually made from woven polypropylene.15 Interestingly, this material, if used, could in principle be converted to rocket fuel, or to power dust distribution, just by addition of oxygen.16
Apollo 17 astronauts saw dust clouds levitate from the lunar surface. The cause has been confirmed by NASA scientists as the repelling of positive charge each grain receives from the sun’s UV and X-ray radiation.17 If dust grains become stuck together after the high g-force of spin launch, they will need to be separated, or de-agglomerated, for efficient light blocking. An example option for dust de-agglomeration and distribution will be sketched next. Without modeling and space-based testing, however, this technology option has the least direct evidence for its viability and is presented here only to suggest the plausibility of a solution.
Since many industrial processes require dust grains to be separated, more than a half-dozen basic device concepts for de-agglomeration of particles are in production use; however, the most effective underlying mechanism is apparently causing dust to impact a solid surface.18 The “Malvern G3,” for instance, de-agglomerates by a puff of pressurized air that forces the dust first against a surface and then into a chamber.19 The result is a column of dust in gas, like those seen heading straight up in some volcanic blasts and in nuclear tests.20
The thirteenth-century Chinese “fire lance” was simply a tube loaded with particles expelled by an explosive shock wave. Special effects in movies use a similar mortar. This concept could be adapted to first send the dust against a surface aboard the spacecraft and then out into a distribution chamber. As dust is propelled from the chamber in a gas stream, the spacecraft would be traveling at equal speed in the opposite direction—like laying a bead of paste on a fixed toothbrush by moving the tube in the direction opposite the exit of the paste. In this way the dust should remain stationary relative to L1. However, L1 is not stable as a balancing point, and so the dust would drift to the sun after a few months.20 Dust would be replenished in an ongoing series of deliveries, possibly targeted to different locations around L1 to change the shading by season.
Because of the dark gray color of moon dust, which reflects little light, it fortuitously has low sensitivity to radiation pressure from the sun. This lets it be positioned slightly sun-side of L1.21 Since the earth-moon system’s center of gravity orbits the sun, Earth has a monthly wobble relative to L1.23
Assessments of technological readiness are not new to NASA or other similar agencies; they have nearly five decades of experience with a methodology for making such assessments.‡ An initial assessment is typically followed by a process of competing proposals for feasibility studies, such as, in the US, the so-called SBIR (Small Business Innovation Research) Phase 1. The readiness levels for the major system components of the present proposal are high, especially compared to previous grand challenges. The possible exception is dust dispersal, which is a perfect candidate for the full process. (The SBIR grant process has already been successfully applied to dust collection and filtering on the moon.27) The larger-scale challenge, that of coordinating the development of the major subsystems so that they integrate into a functioning system, is addressed by the competition structure, which aims to encourage early work on integration wherever possible.
‡ NASA created the “Technological Readiness Level” or TRL, widely used in assessing mission readiness of technologies.24 The major critical subsystems of AstroCool have “TRL levels 6-7 System Development”: SpinLaunch arguably earned “TRL 6 Demonstrated in a relevant environment” for one subsystem (package launching to L1); whereas DART earned “TRL 7 demonstration in a space environment” for the other subsystem (interception and transport spacecraft). The two supporting but still critical subsystems have many possible engineering solutions; however, two demonstrations have earned “TRL 2-4 Research/Development”: “TRL 4-5 Validation in laboratory/relevant environment” for one subsystem (dust filtering)25 and “TRL 2-3 concept or analytical and experimental critical function” for the other subsystem (dust dispersal).26
The approach appears far more feasible than earlier space grand challenges, not least because it is unmanned and its major subsystems have already been put to use. Hopefully, then, it will not require too much time between competition start and reduction of global heating. Its scale, however, goes far beyond previous individual space missions, and may be similar to the annual total of communication satellite missions; but it is dwarfed, as noted earlier, by worldwide fossil fuel extraction. Even without considering spin-offs, cost reductions, and future opportunities it may facilitate, simply as a matter of life or death for society, it seems a small price to pay.
CONCERNS
There are several potential concerns. Most have already been raised with respect to other specific proposals or aimed generally at whole classes of related solutions.28 What follows is a brief but hopefully comprehensive summary of the primary concerns. However, it is worth restating that—in view of the extraordinary cost of any lost time—exploring and debating these concerns can and should be done in parallel with phase one.
First of all, there is a potential concern that AstroCool could reduce the urgency of the change to a more sustainable global system. However, the concern itself reveals a counter-scenario: that absent AstroCool, the imminent total-crisis mode might easily distract attention from a medium-term solution like AstroCool, which could have obviated the crisis in the first place. Simply put, Astrocool, by temporarily reversing atmospheric heating, gains humanity time to transition away from fossil fuel use and from other activities that cause deforestation, desertification, habitat destruction, and biodiversity loss. The transition will require a concerted planetwide political, social, and technological effort unprecedented in history. But it can be encouraged by the success of a referendum-based climate initiative like AstroCool. Furthermore, as detailed later here, AstroCool phase four will apply its open-competition structure to exploring new approaches to removing existing carbon dioxide.
A well-founded concern is that AstroCool only solves part of the problems caused by carbon pollution. Most prominently, it does not address ocean acidification, which together with warming is severely damaging marine life, from coral reefs to phytoplankton. Measures specifically aimed at acidification have been shortlisted by the National Academy of Sciences, including some already being tested in the field.29 Stimulating the development of ocean decarbonization methods will be part of AstroCool phase four.
The United Nations conventions on environmental modification technology30 raise the potential concern of legal obstacles. These conventions are aimed at proposed solutions to the global heating problem that involve disseminating substances or devices on the ground, in the oceans, in the atmosphere, or in near-earth orbit. As the solution here involves activity only on the moon and then about a million miles from Earth, the kinds of risks the conventions are intended to address arguably would not apply. In any case, diffusion of sunlight, even by the small percent proposed here, has been found to have a positive effect on the environment by stimulating photosynthesis.31
A potential concern for some scientific research efforts is that the dust field might disrupt instruments near sun-earth L1. Currently a solar observatory is located near L132; however, it will run out of fuel before 2024; also, it is in a “Halo” orbit about L133 and might therefore avoid the disseminated dust. The proposed asteroid observatory at that location34 could use a suitable such orbit.
Another concern from a technical perspective is that there is always risk. No amount of ground-based studies and space-based testing can completely ensure a successful mission. There are not only known unknowns but potentially also unknown unknowns. One good thing about AstroCool is that it is more robust than an “all or nothing” kind of mission. If some parts fail, there should be ample opportunity to change them and keep on deploying. Also, the project is separable into parallel efforts, both with respect to technology alternatives and to actual deployment by multiple competing teams.
Two apparently contradictory concerns have previously been raised. One, aimed at various shading technologies, is that if they were to suddenly cease functioning, there might be rapid warming that would make adaptation or mitigation difficult or impossible. The other is that if something put in place proved detrimental, we might not have the ability to remove it. Dust near L1 can be placed in orbits35 that would remain stable for many years; however, it can also be placed so as to drift off toward the sun within a few months.36 Thus, the technology exists to address either concern; but no technology can perfectly address both simultaneously. Because of the low operational cost once the infrastructure described is in place, the novel approach suggested here is that dust simply be allowed to drift off and be replaced periodically.
The cooling effect from the solution presented here thus need not be provided uniformly, neither over time nor across the globe.37 The technology allows, depending on the engineering solution, ways for those controlling the system’s operation to influence the distribution of effects, both geographically and by regional season. This might be a huge advantage in achieving an environmentally and politically optimal solution. It could also be considered potential leverage that one or more nations or regions might unfairly apply to the detriment of others. Avoiding all such geopolitical trouble and employing the possibilities to achieve equity in the solution is the aim of the proposed global referenda.
MOVING FORWARD WITHOUT DELAY
The very recent major technological achievements mentioned earlier—spin-launching objects into space and using spacecraft to intercept spaceborne objects—present us now with a new, hopefully just-in-time, opportunity to avoid an environmental apocalypse. Hence the question before us at this auspicious moment, is: Will we tolerate this new opportunity being delayed, such as by slow-walking it to serve the short-term interests of a few, as has occurred historically? Or will the majority interest prevail, thereby also doing right by the dreams of our ancestors and future generations?
We don’t yet know just exactly how feasible, quick to implement, or expensive Astrocool will be. But the only way to establish these parameters is in fact to conduct phase one—ground-based proof of concept—which presents absolutely no risk and where costs are born by contestants and the private sector. In parallel with (not before!) phase one, we can establish whether the concept has worldwide support by carrying out the first global referendum using sample voting. Only once the winning teams have demonstrated feasibility, via first ground-based and then space-based testing, will at least a second referendum, which includes the cost and timing parameters, ask for global approval to start operations in phase three.
Lowering regional and global atmospheric temperatures back to what they were two centuries ago will reduce the frequency and severity of droughts, storms, floods, and fires. It should also: halt and possibly start to reverse the melting of Arctic and Antarctic ice; slow ecosystem destruction and extinctions caused by rising temperatures and droughts; aid in large-scale reforestation and “re-wilding” of land to trap carbon and salvage local and regional ecosystems; give countless heat-threatened plant and animal species a chance to recover; and permit all sorts of mitigation and repair to be carried out.
Meanwhile, the trillions of tons of carbon, mostly in the form of CO2, that have been added to the atmosphere over the last decades, will continue to trap the sun’s heat, even if we were to stop adding carbon tomorrow. No remotely feasible way to rapidly reduce that volume is yet known. The ecosystem damage—weather disasters, sea-level rise, deforestation, mass extinctions, climate-forced human migration—will not stop because we stop adding more carbon to the world’s air and water. We would have merely stopped making it worse. A longer-term solution, for which AstroCool can buy time, is clearly needed.
A global competition for design and implementation of large-scale carbon extraction is well timed as a follow-on to, and leveraging lessons learned from, AstroCool’s first competitions. This is planned as AstroCool phase four.
CONCLUSION
As discussed, there is no good reason to delay starting AstroCool phase one: checking, by teams of experts performing critical design reviews as is done in aerospace, of written proposals. If there are sound, detailed proposals, teams ready to deliver earth-based proofs of concept, and solid public support, then we will be ready to move expeditiously towards space-based testing in phase two and ultimately to igniting the phase-three operational rocket engines. What we cannot afford is delay of the opportunity for teams to prove that they can, at least on paper as a first step, get the job done. Cooling sooner would be of immense value, and delaying cooling of inestimable cost. More subtle and perhaps equally profound benefits to what is proposed here, however, include bringing the planet together around solving global warming and thereby pioneering a way to address other global problems including existing carbon. AstroCool can win us time to enter a truly new era—with humanity pulling together to protect humanity.
Appendix I
PROJECT PLAN AND COMPETITION RULES
The AstroCool project is in four overall phases: ground-based proof of concept, space-based proof of concept, operational deployment, and carbon-capture investigation. The effort in each of these phases is divided into three full-time parallel streams, as detailed below: (A) overall infrastructure and public information; (B) interceptor and dust dispersal drones; and (C) moon dust packaging and launch. Phase four only involves stream (A). Streams (B) and (C) will be able to enter phase two separately as soon as each stream is ready, but phase three entry requires all three streams.
The AstroCool Public Benefit Corporation will conduct part (A) of the project and aims additionally to financially back and potentially incubate non-self-funded entrants for (B) or (C) and share in their rewards.
(A) Overall Implementation and Public Information
AstroCool Public Benefit Corporation’s stream will lead an effort to: (i) conduct a global referendum in phase one to gain commitment from governments for phases two and three, contingent on the technical evaluations continuing to establish safety and feasibility in phases one and two; (ii) provide secure remote voting and discussion forum infrastructure for technical evaluations and project governance; (iii) provide completely transparent forum infrastructure for discussion and evaluation of general concerns during the entire project lifecycle; (iv) provide private negotiation infrastructure for team formation and transparent management of competitions between teams for (B) and (C) below; and (v) promote public participation in the referendum and project generally, including by events, media, grants, and prizes.
Additionally, a patent and software pool will be administered by this stream to incentivize contributions, including from those not competing in a team, and ensure that all teams can use the technology contributed by or available to other teams (like the semiconductor patent pools that have allowed Moore’s law).
Proposals and performance in streams (B) and (C) are reviewed by so-called “Critical Design Reviews” (CDRs)—formal reviews conducted live by subject-matter experts according to accepted engineering and aerospace practice. As provided in (ii) above, reviewer questions and comments in these reviews can be submitted anonymously; similarly, voting will be anonymous to reduce inhibition and measures taken to reduce improper influence of reviewers. The reviews and reviewer selection process will be transparent and ideally allow public input.
(B) Moon Dust Packaging and Launch
An open competition to design and build robotic devices to collect and filter lunar dust into suitable packaging and to launch the dust packages into a suitable orbit to reach L1. Its judging criterion is: “Likelihood of capability to deliver adequate quantities of suitable dust to L1.”
Teams declare initially whether they are addressing either half or all of stream (B). One half, B1, is dust filtering and packaging; the other half, B2, is package launching to L1. B1 and B2 teams can partner to complete the entire stream (B) at any point but must do so before entering (III) below.
This stream comprises three CDR review points:
(I) Entry into phase one—Initial proposals are evaluated by CDR and those judged most promising are recognized as candidates and are eligible to receive grants or investment. Teams must declare their scope as either B1, B2, or B.
(II) Completion of phase one and admittance into phase two—Candidate teams work toward readiness for launch, completing their portion of the first phase of the overall project, by achieving analytical, simulation, and experimental milestones and potentially receiving corresponding grants or investments, as determined by CDRs. Included here are optional B1-C2 and B2-C1 pre-integration CDRs.
(III) Winner of phase two—The first team judged by a CDR as ready to deliver and then assemble filtering, packaging, and launching on the lunar surface is declared the provisional part B winner. However, if the first team’s mission fails in the actual lunar-surface test of phase two, the second team can be deployed, and so on as needed. The first team to pass safety and B-C compatibility CDRs and succeed in delivering packaged dust to L1, independent of whether that team participated in phase one, is the winner of the project’s third-phase part B operational commission.
(C) Interceptor and Dust Dispersal Drones
An open competition stream to build and deliver drone craft to space that can distribute dust in the target area. Judging criteria are: “Likelihood of capability to intercept packaged dust and suitably disperse it in designated locations near L1.”
As with (B), teams declare initially whether they are addressing either half or or all of stream (C). C1 is interception and transport drones; C2 is dust dispersal. C1 and C2 teams can partner to complete the entire stream (C) at any point but must do so before entering stage (III) below.
Also as in stream (B), this stream comprises three CDR review points:
(I) Entry into phase one—Initial proposals are evaluated by CDR and those judged most promising are recognized as candidates and are eligible to receive grants or investment.
(II) Completion of phase one and admittance into phase two—Candidate teams work toward readiness for launch, completing their portion of phase one of the overall project, by achieving analytical, simulation, or experimental milestones and potentially receiving additional corresponding grants or investments, as determined by CDRs. Included here are optional B1-C2 and B2-C1 pre-integration CDRs.
(III) Winner of phase two—The first team judged by a CDR as ready to launch and meeting the criteria is declared the provisional part C winner. However, if the first team’s mission fails in phase two, the second team can be deployed, and so on as needed. The first team that passes safety and B-C compatibility CDRs and succeeds in meeting the criteria by intercepting dust packages and distributing suitably at L1, independent of whether that team participated in phase one, wins the project’s operational third-phase part C operational commission.
An overriding principle of the entire phase three competition is that if any team demonstrates that it can get sufficient light-blocking means to L1 on an ongoing basis, no matter how they accomplish it and independent of any participation in any other aspect of the competition process, that team can win the overall operational commission. A final overriding principle is that if more than one team is poised to win the operational commission of B and/or C, a special CDR will be held to select a dynamic allocation plan for teams to share phase-three operations.
(D) Carbon Capture Investigation
Cooling the atmosphere addresses the primary symptom. But addressing the cause means not only winding down and essentially halting new carbon emissions but extracting billions of tonnes of already released carbon compounds from the air and the oceans. The contest infrastructure created for AstroCool, with appropriate modifications and new sources of expertise for CDRs, will already be in place, as will the system for global sample-voting referenda. That said, the contest will be significantly different as a process because it is completely open-ended.
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[37] MacMartin, D. G., Keith, D. W., Kravitz, B., & Caldeira, K. (2013). Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing. Nature Climate Change, 3(4), 365-368.
[39] https://medium.com/life-on-the-other-planets-whats-new/creating-a-viable-cislunar-economyeb37482f88fc
[40] https://www.nasa.gov/directorates/spacetech/centennial_challenges/nasa-announces-newestwinners-in-break-the-ice-lunar-challenge.html
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