Recently, a company by former SpaceX employee Ben Nowack – called Reflect Orbital – announced that it is now ready to put gigantic mirrors in space to reflect sunshine at ground-based solar farms. This is an idea that’s been around for a hundred years already, both for purposes of defeating the night through reflecting sunshine onto the surface, as well as to reject the same sunshine and reduce the surface temperature. The central question here is is perhaps what the effect would be of adding or subtracting (or both) of solar irradiation on such a large scale as suggested?

We know the effect of light pollution from e.g. cities and street lighting already, which suggests that light pollution is a strongly negative factor for the survival of many species. Meanwhile a reduction in sunshine is already a part of the seasons of Autumn and Winter. Undeniable is that the Sun’s rays are essential to life on Earth, while the day-night cycle (as well as the seasons) created by the Earth’s rotation form an integral part of everything from sleep- and hibernation cycles, to the reproduction of countless species of plants, insects, mammals and everyone’s favorite feathered theropods.

With these effects and the gigantic financial investments required in mind, is there any point to space-based mirrors?

Night-Be-Gone

Of all proposed space-based reflectors and deflectors, the only one to make it past the theoretical stage into testing is the Soviet-era Znamya (‘banner’) satellite. This was originally a solar sail project by Vladimir Syromyatnikov, who would try to get funding for it by pitching it to the USSR leadership in 1988 as a way to bring sunshine to the northern regions of the USSR with their short, cold days. This would extend daylight hours for outdoor work, and potentially also find uses in metropolitan settings, effectively driving night away and removing the need for street and indoor lighting.

Not too long after this Znamya 2 project began, the USSR collapsed, but like so many parts of the USSR space program, Znamya 2 would coast into the uncertain years of the 1990s under the auspice of newly formed Russian companies. With the USSR’s Mir space station still in orbit, it was the ideal platform from which this satellite could be launched. When in February of 1993 this experiment took place, it was considered a success, with the satellite unfolding its 20-meter mirror and casting a roughly 5 km diameter spot of reflected light over pre-dawn Europe.

Yet as if the atmosphere was making a statement, it was cloudy that day over Europe, and those on the ground did not observe much of this new light in the sky, which was said to be on par with that of the full Moon. Following this experiment, the Znamya 2.5 satellite was prepared, with a larger mirror. Unfortunately, the deployment of this satellite failed, with the mirror getting caught on an antenna of the Progress spacecraft. After failed attempts to free the mirror, the satellite was deorbited and along with Znyamya 2.5 the program went up in ashes.

What would have been the impact if the USSR and its successor state had launched hundreds or even thousands of Znamya satellites into orbit?

Light Pollution

How would a world without night fare? This is not an entirely theoretical question either, as those who live at or near the Earth’s poles are well aware of. Yet it’s not simply a matter of day or night, with the sky brightening during night time around the globe a little bit more each year. At this point over a third of the world’s population cannot see the Milky Way any more at night, which is not just a cosmetic inconvenience, but also has very real implications for human health. Much of this is due to how it affects the circadian rhythm and aspects of it, such as the production of melatonin.

An increasing body of evidence supports the notion that exposure to (artificial) light during night time suppresses the production of melatonin, which can have a range of undesirable effects, including poor sleep and even the development of cancer. A 2018 review study by Leena Tähkämö and colleagues in Chronobiology International finds that even an increase in background lighting levels (even with one’s eyes closed) can affect one’s circadian rhythm. This is also an issue with pregnant women, a 2021 study by Karin Windsperger, MD and colleagues in Birth on the ease of delivery and health of newborns describes. Since melatonin passes through the placenta, a disrupted maternal circadian rhythm will thus also negatively affect the development of the fetus.

The ecological impacts of a decreasing night amidst phenomena like skyglow range from new selective pressures on night-time insects and mammals – e.g. decreased effectiveness of camouflage – to the risk of extinction of entire species, such as with newborn turtles who only know to move away from the darkness (the coast) and towards the lighter area (moon-lit ocean), but end up crawling onto brightly lit roads instead where they all too often find their early demise. The case of the Post Tower in Bonn, Germany, clearly demonstrates how birds can be disoriented by light pollution from buildings and consequently collide with said buildings.

Eternal Day

Most recently, the focus with space mirrors appears to based on addressing the primary issue with photovoltaic solar farms, being their lack of production when night falls. Much like how Soviet planners imagined loggers and farmers productively working in eternal daylight, so too would today’s solar farms produce power around the clock. Although Reflect Orbital hasn’t released many – if any – details on what their proposed satellite constellation would look like, a (EU Horizon 2020 grant-supported) 2024 study by Onur Çelik and Colin R. McInnes, as published in Acta Astronautica, titled A constellation design for orbiting solar reflectors to enhance terrestrial solar energy details a few deployment approaches.

This paper suggests initially 20 space mirrors in sun-synchronous orbits at the dawn/dusk terminator, in a fairly typical Walker constellation. What’s not typical is that instead of the satellites trying to blend into the darkness of space, they’d instead do the equivalent of a satellite flare cranked up to well over 9,000. Rather than a glint that may upset an astronomer trying to capture the night sky, instead it’d blast a fairly narrow beam of sunlight at the Earth’s atmosphere. Since the Earth’s atmosphere is not an optically transparent medium, but instead refracts and diffuses light (hence Rayleigh scattering and blue skies), this would create a skyglow from Hell if you’re an astronomer.

Just that one aspect ought to be enough to disabuse anyone of the notion of trying space mirrors for chasing the night away. When it is not ruining astronomy even further, the other aspects of human health effects, ecological destruction and whichever exciting consequences we’d stand to discover as a result, the sheer cost and complexity of putting these massive mirrors into space and controlling them should give anyone pause.

Aiming space mirrors at the Earth and hitting a few PV solar farms is a feat where, if you pay attention, the marketing and studies never seem to mention clouds, fog or other weather events that make sunshine not reach the Earth’s surface as well. Meanwhile we got low-carbon power sources that do not require space mirrors or ecological destruction to produce 24/7.

Reclaiming The Night

If it’s solar that you want, but the lack of 24/7 production has you down, then concentrated solar power (CSP) has been around for a while. Although the tower-based form of CSP, like Ivanpah in the Mojave desert, have a bad rap if only for their bird-killing powers, parabolic-trough CSP circumvents many of the issues, including less complicated solar tracking, due to the parabolic part. CSP generally comes with its own thermal storage system, which gives CSP built-in energy storage for hours and thus makes it a dispatchable source of power.

Although storage-less PV solar used to get a higher return, dispatchable power sources are more highly valued these days, which is whwy CSP is making a comeback. These solar plants will happily produce power during the night from their stored heat, although they do best in areas with a lot of sunshine. Much like the non-solar option of nuclear and hydro dams, these do not share the main flaw that makes PV solar such a pain to manage, while being dispatchable, low-carbon and do not ruin the night and astronomy more than we have already managed so far.

Considering the importance of maintaining the day-night cycle on Earth based on the evidence we have available, it is hoped that we never see space mirrors become a reality, and instead we can focus on technologies that will really make life better on Earth. Or, if we really want to do PV solar and satellites, we can burn a big stack of money on space-based solar while leaving precious night time intact.

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• Source: https://hackaday.com/2024/04/03/space-mirrors-dreams-of-turning-the-night-into-day-around-the-clock/