Light pollution is increasing over much of the world. It is a trend that goes back decades and shows no sign of slowing down. We wrote here about the situation as recently as early 2023. At that time, new research showed that skyglow was then increasing at a worldwide average rate of 10 percent each year. A much newer notion is the idea of 'light pollution' from space. We also wrote about that situation in 2023. The concern was then about the changing appearance of the night sky. 

Fast forward only two years, and a completely new concern is now emerging. What happens when satellites can turn night into day? The result is a novel threat we explore in this month's post.

We live in an era some that some call "New Space". This describes activities in outer space dominated by private commercial actors. It contrasts with previous decades when only national space programs could pay the high cost of launch.

That cost plummeted in the 2010s, enabling private companies to launch payloads into space. At first, the main service private satellites provided was global telecommunications. But as investor money poured into the industry, entrepreneurs began to come up with audacious new ideas.

One of those ideas is to harness solar power in space and send it to the ground. This takes different forms including converting sunlight to radio waves. A simpler concept would deploy large reflective surfaces in orbit around the Earth. These would redirect sunlight to the ground to illuminate solar power stations on the ground. The scheme only works near sunrise and sunset, when the reflectors are in sunlight but the sun has set on solar farms.

Proponents of this technology note that it can provide light for other uses. For instance, they say, it could function in place of street lighting over cities. It would provide an illumination level about four times the brightness of full moonlight. That could aid in disaster recovery when utility power is unavailable.

You would be forgiven for thinking this is the first time anyone has proposed such a thing. But it's not. In the Second World War, a group of German scientists at the German Army Artillery proposed building a Sonnengewehr ("sun gun"). They designed a focused beam of sunlight from an orbital reflector as an offensive weapon. And they expected the devastation to be akin to what the world later saw resulting from the U.S. atomic attack on Japan.
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In October 1992, the Russian Federal Space Agency launched the Znamya 2 satellite. Designed as a 'solar sail' testing a new kind of propulsion, the RFSA repurposed it as a 20-meter-wide solar mirror. It consisted of panels of stretched, highly reflective film that deployed after launch.

During a demonstration of the technology, it successfully directed a beam of sunlight to the ground. It yielded a spot 5 kilometers wide with the intensity of full moonlight. The beam swept across Europe from southern France to western Russia at a ground speed of 8 kilometers per second. Though weather along much of the ground track was cloudy, some observers reported seeing bright flash of light as the beam swept past them.

The RFSA tried another test of this technology in 1999 with a larger spot size and a brighter beam. The test failed when the reflective film panels tore after snagging a piece of the Progress spacecraft used to deploy the object. Although the RFSA planned future satellites with even large collecting surfaces, the 1999 failure was the death knell for the program.

More than 25 years later, the concept is again inching closer to reality. An American company called Reflect Orbital applied for clearance to launch and operate a test satellite in 2026. It consists of a thin-film reflector 18 meters on a side and a system to control its orientation in space. By changing that orientation relative to the direction of the Sun, it can direct a beam of sunlight toward Earth.

Like Znamya 2, its beam has a diameter of 5 kilometers on the ground, enough to illuminate a large solar power installation. The beam shines for about four minutes before the satellite disappears over the local horizon. The company plans to eventually launch a flotilla of thousands of these reflectors. That would enable continuous sunlight for about an hour after dusk and an hour before dawn.

Will it work? We don't yet know. The Russian test from the 1990s suggests that something like this is technically workable. But if it does, a host of concerns are expected to follow.

Some problems have to do with the idea of shining a beam of light with the intensity of sunlight onto specific locations at night. A simple calculation suggests that the reflectors will appear on the sky as sources several times brighter than a full Moon. Far from the beams, they'll still look like bright stars, and dozens of them may appear in the sky at any moment.

Scattering of light in the atmosphere will make the edges of the beams 'fuzzy'. The mirror-like surfaces of the reflectors will deteriorate with time due to exposure to the space environment. The beams of light they produce becoming more diffuse, spreading out and losing intensity. This may direct light well away from the intended targets of the beams. Some of that light may end up in ecologically sensitive areas.

As described above, the mirrors have to change their orientation in space as they pass over a given location. Although the company claims that the reorientation will happen quickly, it involves sweeping the light beam across the Earth at high speed. A 2000 study published in the Journal of the Royal Astronomical Society of Canada found that "space-mirror experiments reflecting sunlight to Earth can produce resolved images having surface-brightness sufficient to damage human eyes looking through telescopes or binoculars". Even if the flash is instantaneous, it could cause real harm to the viewer.

In a similar vein, these light beams could be a problem for aviation safety. Pilots have for years reported intense flashes of light from laser pointers on the ground shining up at their planes. At the altitudes of commercial planes, beams of sunlight from space will be larger in size and brighter than they appear on the ground. This could become a significant hazard for civilian and military pilots alike.

There is great potential for misuse of this technology. Sunlight could be weaponized in a way that conventional solar power cannot be. It may be directed toward people and communities that don’t want it. It could also be used to convey battlefield advantage in military conflicts. This adds another layer of complexity in deciding how the technology should be regulated.

The reflective material could be subject to fraying or other kinds of damage on orbit. They may shed material that becomes space debris. Over time, the satellites will inevitably fall back to Earth, whether from atmospheric drag or deliberate action to de-orbit them. Where, when and how they will come back down is not clear.
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Lastly, despite prognostications to the contrary, there is no “inevitability” about this or any other idea for furthering renewable energy sources through methods such as sunlight as a service. Improvements in battery storage are slowly improving renewable energy supplies at night. We may be better off deploying more solar panels on the ground, even knowing that there is a life-cycle cost for producing/recycling the equipment. 

"Greenwashing" is a label describing efforts made to persuade the public that an organization's products or actions are friendly to the environment. Usually they are not, and the greenwashing effort is deceptive.

That seems to be happening in the case of sunlight as a service. The sales literature is full of starry-eyed claims having to do with a purported social good. But it focuses on the notion of sustainability in a narrow sense: providing sunlight from space for "clean" electricity generation. It doesn't consider the full lifecycle of the project from launch to de-orbit.

It doesn't account for the negative externalities of directing light to spaces where it doesn't naturally exist at night. There is abundant evidence for the harms associated with artificial light at night. That in principle includes sunlight directed to the night side of Earth. It interferes with natural rhythms as much as sources of electric lighting.

At the same time, there is no national or international prohibition on this kind of activity in outer space. The international legal framework governing activities in space takes the view that 'what isn't forbidden is allowed'. Norms often change to discourage a harmful activity only when the harm has already been inflicted.

In that sense it resembles obtrusive space advertising, which we wrote about here recently. Dangerous activities in space can occur with only an ill-defined liability system on the other side.

It's unclear how serious any of this is, and projects like Reflect Orbital may not fly at all. Many such audacious ideas never become reality. Some are meant only to attract the intention of investors looking to make quick money as companies are bought and sold.
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It remains to be seen whether there is any successful business model for selling "sunlight as a service". Yet the lure of new wealth from space may prove irresistible. This is a challenge for defenders of the night everywhere, and one that is worth watching closely.

It sounds like something out of a bad dream. You're outside in the early evening, enjoying the night air and contemplating the stars. All of a sudden, a glowing message drift across the sky: EAT AT JOE'S. It has all the appeal of a commercial message in a nature reserve. Yet such a scenario may only be a few years away.

​In a previous post here, we asked whether we should worry about satellite light pollution. At that time we argued there was little reason for concern. Yet it's easy to conceive of a future in which it is a problem. We made that argument based on certain realities about shortcomings in how we govern human activities in outer space. "Space advertising" is in even earlier stages of development, but the same anxieties apply. The difference is that for space advertising, there is still time to get out ahead of the situation.

​The uses and occupation of orbital space near the Earth have transformed since 2019. In the time since, the number and pace of launches of satellites into orbit around our planet more than doubled compared to their Cold War peak. An important difference compared to decades ago is that private actors conduct most of these operations. This brings activities motivated by profit rather than, say, geopolitical superiority.

Yet long before the arrival of this new use regime, some eyed outer space as the next frontier of product marketing.  For some, it was enough to engage in product placement on rockets or spacecraft. Others saw space as the medium of advertisement itself.

One notable episode in 1993 involved a proposed orbiting billboard made of Mylar that would appear about half the size of the full moon in the sky. Outcry from astronomers and environmental groups led to an act of the U.S. Congress that prohibited such activity if launched from U.S. territory.

​The 1993 law defined obtrusive space advertising as "advertising in outer space that is capable of being recognized by a human being on the surface of the Earth without the aid of a telescope or other technological device." Congress worded it so to draw a distinction with a more passive form of advertising such as corporate logos on launch vehicles. But in enacting the prohibition, Congress made clear that the U.S. would not abide "obtrusive" commercial messages in space. 

Besides the potential to annoy billions of people, obtrusive space advertising poses a threat to astronomy. To be bright enough for people on the ground to see it, ads in space must be bright. Any such object wandering through the field of view of a telescope would obliterate faint cosmic light beyond. These object would also be bright at infrared wavelengths.

Even if the lights switched off while flying over observatories, dark objects would block starlight for several seconds. There are already concerns that much smaller conventional satellites will have similar effects on astronomical observations.

At the same time, it seems inevitable that someone will try this. The lure of passive income from space advertising is great. It was once the case that the high cost of launching objects into orbit was a disincentive to potential space advertisers. But the recent mass-commercialization of launch services caused per-kilogram launch costs to plummet.

​Another factor is a shift in government attitudes toward commercial activities in space. From its founding, the U.S. National Aeronautics and Space Administration (NASA) faced restrictions on even appearing to promote commercial products or services. That stance is shifting. For example, in 2018 the NASA administrator formed a committee to investigate changing the policy.

Nothing in international law now governs this variety of space advertising. The founding document of international space law, the 1967 Outer Space Treaty (OST), is silent on this topic. It does not prohibit commercial activity in space. In fact, it refers to the "use of outer space", which many construe to include both commercialism and exploitation.

But it doesn't render such activities limitless. Its Article IX calls for "due regard" among spacefaring nations toward "the corresponding interests of all other States Parties to the Treaty". And it considers the possibility that some of those activities could drive conflict. Any activity that "would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space" requires consultations between countries causing and receiving the interference.

The U.S. prohibition on obtrusive space advertising also faces civil liberties challenges. Some assert that the First Amendment to the U.S. Constitution precludes such laws. In their 1995 law review article "People Do Read Large Ads: The Law of Advertising from Outer Space", Don Tomlinson and Robert Wiley came to different conclusions on this point. Tomlinson argued "Ban Without Reservation", while Wiley promoted "Regulate with Reservations".

Still, the world often looks to the United States to lead on international policy matters. The Outer Space Treaty led to the establishment of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). It serves as an international forum for diplomatic discussions of matters flowing from implementation of the OST. At its annual meetings (and those of its subcommittees), national delegations debate various concerns.

​Because COPUOS operates on a consensus basis, the pace of legal conventions over the decades has been very slow. The U.S. and its allies exert an outsized influence in the international community. To that extent they have led efforts to recognize norms of behavior outside the realm of binding, 'black-letter' law.

The American Astronomical Society (U.S.) and Royal Astronomical Society (U.K.) recently asked for exactly that. Both are associations of astronomers that advocate for their members on both national and international matters. In the past year, both issued statements calling for their national delegations to promote discussing obtrusive space advertising at COPUOS. That led to media coverage (e.g., here, here and here) that raised more public attention to the issue.

A particular episode spurred them on. As the AAS statement notes, "Avant-Space Systems LLC, a private entity incorporated in the Russian Federation, recently launched a prototype cubesat intended to demonstrate the feasibility of this technology." Avant-Space launched a 3U cubesat in April 2024 to test objects that would make glowing message formations in space. The successful effort made the prospect of near-term advertising missions palpable.

The AAS statement calls out two specific aspects of the OST. First, it declares that astronomy is a kind of Article I "use" of outer space. And second, as a result Article IX dictates that it is entitled to "due regard" from launching States to limit harmful interference.

But it goes further. Because "no known mitigation of such harmful interference enables the peaceful co-existence of obtrusive space advertising alongside astronomy consistent with Article IX", it argues that States should simply prohibit launch of such payloads from their territories. That's exactly what U.S. law already demands. AAS thus asks the U.S. COPUOS delegation to promote the same policy worldwide.

The RAS takes a similar stance, noting that the Society "opposes all space-based advertising, recognising it as detrimental to the science of astronomy and to our shared heritage of the night sky". It references the 2007 Declaration in Defence of the Night Sky and the Right to Starlight, a nonbinding statement supported in part by the United Nations Educational, Scientific and Cultural Organization (UNESCO). That document called an unpolluted night sky "an inalienable right of humankind equivalent to all other environmental, social, and cultural rights."

It also builds on moves the international astronomical community made almost a quarter-century ago. In its 2001 COPUOS statement, the International Astronomical Union (IAU) referenced the 1993 U.S. obtrusive space advertising prohibition. It called on COPUOS to encourage member States to "adopt similar legislation on obtrusive space advertising, so that this activity is regulated by all space-faring nations."

​This month, the COPUOS Science and Technology Subcommittee will hold its annual meeting in Vienna, Austria. At that meeting, it will hear again from the IAU: "[T]here is no means of mitigating the potential harm to astronomy of obtrusive space advertising.  It represents the ultimate light trespass because its purpose is to be visible as widely as possible on the surface of the Earth.  The IAU urges COPUOS national delegations to consider a prohibition on this technology that creates the risk of unwanted messaging and disruption of the dark night sky."

No one yet knows whether COPUOS will take this advice to heart. Reading the diplomatic tea leaves is often difficult. But this effort may well have the majority of public sentiment on its side. As effective as advertising is, many people tire of being targets of a nonstop, 24-hour-a-day marketing regime. Especially given the proliferation of electronic media and mobile devices, their waking hours are often bombarded with commercial messages. And for some, the notion of advertisements brightening the night sky beyond the pale.

The world faces an imminent choice. It can allow this kind of activity in space, or it can prevent it from ever taking root. If it chooses the former, experience shows that it will be difficult to put the proverbial genie back in the bottle. Of course, a rogue actor could (and may well) launch an space advertisement in violation of domestic law. Some argue against the very notion of law in space to begin with; others note that the OST enforcement regime has no effect at the international level. It remains an evolving geopolitical matter.

The night sky is one of the few remaining aspects of the natural world that all humans share. Our increasingly connected world has blurred other boundaries, but the sky remains a kind of public commons. Whether the world will assert proper control over that commons remains to be seen. But if we lose that shared sense of ownership by allowing narrow commercial interests to take it over, we will have lost something much more significant: a rare medium that draws us together more than it pushes us apart.