April 13, 2024

Space mirrors: dreams of turning night into day 24 hours a day

Recently, a company owned by former SpaceX employee Ben Nowack – called Reflect Orbital – announced which is now ready to place gigantic mirrors in space to reflect sunlight into terrestrial solar farms. This is an idea that has been around for a hundred years, both to defeat the night by reflecting sunlight off the surface, and to reject the same sunlight and reduce the surface temperature. The central question here is perhaps what would be the effect of adding or subtracting (or both) solar irradiation on such a large scale as suggested?

We already know the effect of light pollution, for example from cities and public lighting, which suggests that light pollution is a strongly negative factor for the survival of many species. However, the reduction in insolation is already part of the autumn and winter seasons. What is 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 is 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.

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

Night that goes away

The Znyamya 2 space mirror in orbit. (Credit: RSC Energia)

Of all the proposed space reflectors and deflectors, the only one that made it from the theoretical phase to testing was the Soviet-era one. Znamya (‘banner’) satellite. This was originally a solar sail project from Vladimir Syromyatnikov, who would try to obtain funding by presenting it to the USSR leadership in 1988, as a way of bringing sunlight to the northern regions of the USSR with its short, cold days. This would extend daylight hours for outdoor work and potentially also find use in metropolitan environments, effectively moving away from night and eliminating the need for public and indoor lighting.

Not long after the start of this Znamya 2 project, the USSR collapsed, but like many parts of the USSR’s space program, Znamya 2 would reach the uncertain years of the 1990s under the auspices of newly formed Russian companies. . With the USSR Mir space station still in orbit, was the ideal platform from which this satellite could be launched. When this experiment was carried out in February 1993, it was considered a success, with the satellite unfolding its 20-meter mirror and projecting a patch of reflected light about 5 km in diameter over Europe before dawn.

However, as if the atmosphere was making a statement, that day was cloudy 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 stuck in an antenna on the Progress spacecraft. After failed attempts to free the mirror, the satellite was deorbited and together with Znyamya 2.5 the program went into 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

Increased artificial brightness of the night sky in North America (Source: Ron Chepesiuk, 2009, Environmental Health Perspective)

What would a world without night be like? This is also not an entirely theoretical question, as those who live at or near the Earth’s poles know. However, it’s not simply a matter of day or night, with the sky shining a little brighter at night around the world every year. Right now, more than a third of the world’s population can no longer see the Milky Way 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 melatonin production.

A growing body of evidence supports the notion that exposure to (artificial) light at night suppresses melatonin production, which can have a number of undesirable effects, including poor sleep and even the development of cancer. A 2018 review study by Leena Tähkämö and colleagues in International Chronobiology finds that even an increase in background lighting levels (even with eyes closed) can affect the circadian rhythm. This is also an issue with pregnant women, a 2021 study by Karin Windsperger, MD and colleagues in Birthday about the ease of childbirth and the health of newborns describes. As melatonin passes through the placenta, a disruption of the maternal circadian rhythm will also negatively affect the developing fetus.

The ecological impacts of a decreasing night in the midst of phenomena such as skyglow range from new selective pressures on nocturnal insects and mammals – for example, reduced camouflage effectiveness – to the risk of extinction of entire species, as happens with newborn turtles. who only know how to stay away. out of the darkness (the coast) and toward the brighter area (moonlit ocean), but end up crawling along brightly lit roads, where they often meet their early demise. The case of the Post Tower in Bonn, Germany, clearly demonstrates how birds can become disoriented by light pollution from buildings and consequently collide with those buildings.

Eternal Day

24-hour Earth track of selected optimal Sun-synchronous orbit. (Credit: Çelik et al., 2024)

More recently, the focus on space mirrors appears to be based on solving the main problem of photovoltaic solar parks, which is the lack of production at nightfall. Just as Soviet planners imagined loggers and farmers working productively in eternal daylight, so today’s solar farms would produce energy 24 hours a day. While Reflect Orbital has not released many – if any – details about what the proposed satellite constellation would look like, a 2024 study (funded by the EU’s Horizon 2020 program) by Onur Çelik and Colin R. McInnes, published in Astronautical Actentitled A constellation design for orbiting solar reflectors to increase terrestrial solar power details some implementation approaches.

This paper initially suggests 20 space mirrors in Sun-synchronous orbits at late dawn/dusk, 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 would do the equivalent of a satellite flare boosted to well over 9,000. Instead of a glow that might disturb an astronomer trying to capture the night sky, it would cast a fairly narrow beam of sunlight into Earth’s atmosphere. Since Earth’s atmosphere is not an optically transparent medium, but instead refracts and diffuses light (hence Rayleigh scattering and the blue sky), this would create a celestial glow from Hell if you were an astronomer.

That aspect alone should be enough to disabuse anyone of the notion of trying space mirrors to chase all night. When it’s not further ruining astronomy, the other aspects of human health effects, ecological destruction, and whatever exciting consequences we might discover as a result, the cost and complexity of putting these enormous mirrors in space and controlling them should give anyone takes a break.

Pointing space mirrors at Earth and hitting some solar photovoltaic farms is a feat where, if you pay attention, the marketing and studies never seem to mention clouds, fog or other weather events that cause sunlight to not also reach the surface from the earth. However, we have obtained low-carbon energy sources that do not require space mirrors or ecological destruction to produce 24/7.

Recovering the night

Part of the 354 MW SEGS solar complex in northern San Bernardino County, California

If it’s solar power you want, but the lack of 24/7 production has you feeling discouraged, then concentrated solar power (CSP) has been around for a while. Although the tower-based form of CSP, like Ivanpah in the Mojave Desert, has a bad reputation, if only for its bird-killing powers, the parabolic trough CSP gets around many of the problems, including less complicated solar tracking, due to the parabolic. The CSP usually comes with its own thermal storage system, which provides energy storage integrated into the CSP for hours and thus makes it a dispatchable power source.

While storage-free solar PV used to get a higher return, dispatchable power sources are more valued today, which is why CSP is making a comeback. These solar plants will produce energy at night from stored heat, although they perform best in areas with lots of sun. Like the non-solar option of nuclear and hydroelectric dams, these do not share the main flaw that makes solar photovoltaics so difficult to manage, while at the same time they are dispatchable, low carbon and do not ruin the night and astronomy any more than we already did. 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 will never see space mirrors become a reality and instead can focus on technologies that will truly make life best on Earth. Or, if we really want to do solar photovoltaics and satellites, we can burn a big pile of money on space solar, leaving precious nighttime untouched.

Leave a Reply

Your email address will not be published. Required fields are marked *