Free balloons, strings attached

In this issue

Is this the bubble-pop we should really be worried about?

🎈  The pitch: A two-person South Dakota startup patented a reusable balloon that carries sulfur dioxide into the stratosphere, where it forms a haze that reflects sunlight and cools the planet.

⚠️  What's new? The day after the patent was granted, Make Sunsets gave it away free to anyone releasing under a ton a year. Bigger users get a cheap licence, paid for in reporting data.

💰  Follow the money: Ten months on, no named licensee has appeared and monthly revenue has slipped. Stardust, the rival patenting its own particles, has raised US$75 million.

📄  The paperwork: US 12,486,031 B2 was granted on 2 December 2025. Florida has since made launching one a felony, and 37 states and Congress have seen ban proposals.

A planet-saving patent, then a giveaway

On 2 December 2025, a two-person South Dakota startup was granted a patent on a way to cool the planet. The next day, the company announced that almost anyone could just use it for free.

Since 2022, the company 'Make Sunsets' has launched more than 200 weather balloons carrying sulfur dioxide into the upper atmosphere, where the gas forms a haze that reflects a little sunlight back to space. It pays for the launches by selling "cooling credits" online.

Companies usually patent things to keep competitors out. Make Sunsets says it patented this one to keep the method open, and to stop a far better funded rival from locking it up.

That makes this issue a little different from our usual. The useful lesson is the strategy around it. Why would a company pay for a patent and then adopt this strategy? And has the move worked ten months on?

We will also explore how the technology has serious critics. Scientists, several governments and three US states want it restricted or banned, and the people living under those balloons don't seem to have much of a say.

Make Sunsets, a startup registered in Box Elder, South Dakota, has a recently published patent for a balloon system that carries liquid sulfur dioxide into the stratosphere, releases it as gas, and comes home for a refill.

The inventor is the founder, Luke Iseman. He got the idea from a science fiction novel while semi-retired in Mexico, spearfishing 20 to 30 hours a week, as he told NPR.

The science he is borrowing is old. When Mount Pinatubo erupted in 1991, its sulfur spread through the upper atmosphere and cooled the planet for a while. Doing that on purpose is called stratospheric aerosol injection.

First, at a ground station (the patent drawings use boats), a small insulated tank is filled with pressurised liquid sulfur dioxide. The patent suggests a tank of about two to four cubic feet.

Next, a balloon is filled with lift gas through its own tether, which doubles as a hose. Up it goes, with small thrusters or a steerable parachute nudging it sideways so the wind is not fully in charge.

At altitude, the liquid passes through a valve into a heated chamber and turns to gas. A second valve meters that gas out through a heated nozzle. The patent also describes a sensor and a tiny wiper blade to keep the nozzle clean.

The gas then reacts with the air and forms fine sulfate particles, which is the reflective haze the whole exercise is for.

The balloon vents some lift gas, sinks, and its base floats on the water until a boat collects it, refills it and sends it back up.

A round trip is what would let launches run on a schedule. The patent describes fleets of these units moving between many stations, each one reporting its location and supplies.

This is a patent-specific description of a system, aka, it is covering the machine the company would like to have. What Make Sunsets flies today is far simpler, being a latex balloon holding about 1.7 kg of gas that bursts at altitude, according to Geoengineering Monitor.

The day after the patent was granted, Iseman posted an announcement on the Make Sunsets blog with three moves in it.

Move one, the giveaway. Anyone releasing less than one ton a year into the stratosphere gets an irrevocable right to use the patented technology, free.

Move two, the toll booth. Anyone above one ton gets a cheap licence, and the company says it might even pay them to deploy. The price is rigorous reporting, sent to Make Sunsets.

Move three, the ambition. The stated plan is to become the world's record-keeper for who is putting what into the stratosphere.

The post also names the motive. Holding the patent stops anyone else from monopolising the method, a pointed reference to the one other company in the field.

This is a known play called a patent pledge. The famous one came in 2014 from Tesla, which promised not to sue good-faith users of its electric car patents. The logic is that a small market grows faster when the entry fee is zero.

If you only want to stop rivals patenting your idea, you can publish it. Published ideas cannot be patented by someone else. Paying for a patent buys something extra, which is the right to attach conditions. Make Sunsets is using that right to demand data.

Inside Climate News counted 147 launches by April 2025, with the biggest balloons holding under 2 kg. The pledge itself is one paragraph on a blog. In Iseman's words, "we are not going to spend money lawyering this up." So the strategy gives away a machine nobody flies, below a volume nobody reaches, in exchange for a seat at a table that does not exist yet.

Cutting emissions works slowly. The carbon already in the air keeps warming the planet for decades, whatever happens to next year's emissions.

Reflecting a sliver of sunlight is the one idea that could, on paper, lower temperatures within a few years. It is also an idea that isn't really permitted to test properly outdoors.

Harvard's planned stratospheric experiment was abandoned in 2024 before a single field test, as Freethink recounts. Make Sunsets exists because its founders decided to skip the permission step.

The cost of skipping it is scale. A balloon carries a little over a kilogram. Hitting a meaningful cooling target that way would take around a billion launches a year, by the arithmetic CBC ran with geoengineering researcher David Keith.

The field of companies trying to sell sunlight reflection is tiny. There are two, and they made opposite bets on intellectual property.

Stardust Solutions is the closest rival and the mirror image. The Israeli-US startup is developing its own silica-based particles to spray from high-flying aircraft, and it is seeking patents on those particles as a core part of the business, according to E&E News. It says it will deploy only if governments hire it and rules exist. Lowercarbon Capital is among its backers.

Where Make Sunsets patented the vehicle and opened it, Stardust is patenting the cargo and keeping it. Critics are not charmed by that either. Shuchi Talati of the Alliance for Just Deliberation on Solar Geoengineering told E&E the company "cannot create their own principles and then applaud themselves for following them."

Voltitude, a UK firm, is the adjacent name to watch. It has UK government funding to build solar-powered micro-balloons that monitor the stratosphere, per Geoengineering Monitor. That is the record-keeper role Make Sunsets wants, pursued with public money and without releasing anything.

Reflective, a philanthropy-funded research group in California, funds modelling and has built a public simulator. Cambridge University is testing alternative particles on balloon and aircraft flights that release nothing.

Then there are the scars. Harvard's SCoPEx experiment folded under protest. A UK group reportedly flew its own sulfur balloon in 2022, MIT Technology Review found, which shows how little a would-be copycat needs Make Sunsets' paperwork.

Serious researchers are funded to avoid releasing sulfur, the serious rival uses planes and its own particles, and hobbyists can pop a balloon unassisted. Who, exactly, is the customer for a free licence to a reusable sulfur balloon?

Make Sunsets essentially sells a cooling credit, as a promise that one gram of sulfur dioxide, released high up, offsets the warming of one ton of carbon dioxide for a year. Geoengineering Monitor, a watchdog that opposes the technology, notes the company offers no scientific evidence for that ratio.

The buyer base is thin. By late 2025 the company reported around 1,000 customers, and more than 70% of all credits had gone to two undisclosed clients. So the retail market is roughly a thousand people and two whales.

Money is arriving in the broader market, though not for credits. Total funding for sunlight reflection research almost tripled in 2025. The UK's research agency ARIA committed £57 million. The Simons Foundation launched a US$50 million fund.

Nearly all of that pays for modelling, monitoring and lab work. Rather, the estimates for what a deployment would cost show how unsettled this category is. Make Sunsets says about US$30 million would offset a year's new warming. Stardust puts a full-scale programme at roughly US$20 billion a year, per Dealroom.

Those two numbers differ by a factor of more than 600. Both companies do agree on the eventual customer, which is a government. Stardust has said so openly. Make Sunsets' licence terms only bite above one ton a year, a volume that implies a state or a very committed billionaire.

That leaves the voluntary market in an odd spot. Advisors to the European Commission have already recommended that cooling credits be barred from counting toward climate obligations, Climate Home News reported.

If regulators will not recognise the credit and governments are the only buyer at scale, what is the viability of a startup like Make Sunsets?

The core harm is simple. One party changes the sky and everyone underneath lives with the result.

Scientists who study the method list damage to the ozone layer, shifted rainfall, lower crop yields and health effects among the possible consequences, as summarised by Geoengineering Monitor. Climate models cannot yet say where those effects would land.

Picture a farmer in Pakistan whose monsoon arrives late. He did not buy a credit and hasn't heard of this scrappy startup. A climate policy expert in Islamabad put that concern to NPR directly, saying the company needs to think harder about people in places like his.

The deeper risk lies in the importance of the patent's refill loop. The particles fall out, so the cooling lasts only while the flights continue. Stop suddenly and the masked warming returns fast, an effect researchers call termination shock.

Now add the IP strategy. A free licence spreads the activity across many small operators, each under the one-ton line without reporting requirements. The only party that would hold the records is a startup with about 14 months of cash, by the latest monthly update from Make Sunsets.

Opposition comes from every direction, for different reasons.

•  More than 500 academics have signed a call for a non-use agreement, and African environment ministers have twice backed one.

•  Researchers who favour studying the idea object to selling it. Keith told CBC the cooling maths is too rough to build a business on.

•  The US EPA under Lee Zeldin sent the company a formal demand for information in April 2025, calling the venture climate extremism. One legal expert told SRM360 the Clean Air Act does not squarely apply.

Mexico said it would ban experiments in 2023. Tennessee banned the practice in 2024. Florida followed in 2025 with a felony carrying up to five years, and Louisiana passed its own ban.

By July 2026, 37 states and Congress had seen ban proposals, according to SRM360, which also notes most have stalled. In Europe, foreign ministers called for a moratorium on deployment in April 2026, Climate Home News reported.

So a Florida hobbyist who accepts the free licence gains the right to build the balloon and a possible prison term for launching it.

Ten months of evidence say the open strategy has not paid, and the closed one has raised about sixty times more money.

What the giveaway produced

We could not find a single named licensee, partner or adopter of the patent since the pledge. If one exists, it has not been announced.

Make Sunsets publishes its finances every month, which makes the scorecard unusually easy to read. In November 2025, the month before the pledge, it reported revenue of US$14,538 and cash of US$802,933.

Customers did grow, from 1,027 to 1,323. That is about 30 new buyers a month.

Iseman wrote in his new year update that the company needed new ideas because it was not growing. The response has been a sideways step. Make Sunsets is now building a low-cost climate sensor to sell and has applied for at least three grants.

Its total venture funding stood at more than US$1.2 million as of 2024, NPR reported.

What the proprietary rival raised

Stardust closed a US$60 million round in October 2025, the largest ever for a company in this field, and has raised US$75 million in total, according to E&E News and Dealroom. Patents on its particles are central to the pitch.

That money has bought lab work and six studies the company says it is submitting for peer review. Stardust has no revenue and no deployment, and its investors are betting on a government contract that no government has offered.

Where the rest of the money goes

The larger cheques avoid companies altogether. ARIA's £57 million programme, the Simons Foundation's US$50 million fund and the Quadrature Climate Foundation's €37 million all back university and nonprofit research.

What's the pattern?

A patent pledge works when other people want to build your thing. Tesla's logic was that a bigger electric car market would help Tesla. Comparatively, a reusable sulfur balloon doesn't really need to be compatible with anything.

There are multiple factors here, from the pledge, to hostile laws and a federal inquiry in the same period. What the numbers do show is that giving the patent away did not offset the difficulties they have faced.

Capital in this field is paying for exclusivity and a government-buyer thesis. Openness has earned Make Sunsets attention, which it already had.

For the person who bought a cooling credit, little changes. The balloons still burst.

The patent's more plausible future is as a bargaining chip. If a government ever commissions balloon-based deployment, Make Sunsets holds a claim on one way of doing it and a licence that demands reporting. That could point to a role as a monitor, which fits the sensor product now in fabrication.

It could also end up as an asset on a sale sheet. A company with 14 months of cash and one granted patent has a short list of things to sell.

We're watching three things:

•  Evidence of whether anyone signs the licence,

•  whether the EPA inquiry resolves, and

•  whether Stardust's particle patents are granted.

This week's patent is US 12,486,031 B2, titled 'Atmospheric Delivery of Particulate Matter', published by Make Sunsets Incorporated.

Read the filing if you like valve diagrams, hit reply and tell us whether the giveaway is smart or empty, and come argue with us on Instagram and LinkedIn.

•  The full patent, claims and all with USPTO: Read claim 1 end to end and count how many separate components a copycat would need to include before infringing.

•  Every US geoengineering ban bill, mapped with SRM360: Explore the state-by-state tracker to see where launching a licensed balloon would be legal, pending or a crime.

•  Why state lawmakers turned on a technology nobody is using with Legal Planet: See a UCLA law scholar trace the unusual political coalition behind the bans.

•  Inside the proprietary rival with MIT Technology Review: Discover how Stardust plans to earn government contracts and why researchers object to its for-profit model.

•  The EPA's letter to Make Sunsets with US EPA: Read the original Clean Air Act demand and judge how well a pollution statute fits a weather balloon.

•  A model for regulating instead of banning with SRM360: Zoom out to a 2026 proposal for state rules that would govern atmospheric interventions without outlawing research.