Reflect sunlight at night with Giant mirrors

Sunlight would be available on demand by Reflect Orbital

Reflect Orbital is a startup company in the US and wants to provide light for solar farms at night, among other uses. The company suggested putting 250,000 satellites into space covered with mirrors in order to achieve their night-lighting goals. Scientists said this plan could be dangerous for astronomers and others. Plus, it still would not adequately achieve the goals they are claiming. A bright sun with rays bursting through past dark trees and landscape. The startup company Reflect Orbital has proposed putting hundreds of thousands of satellites with mirrors in space to illuminate areas of Earth at night. But can it be done? Reflect Orbital promises sunlight on demand. What exactly does that mean and how would it affect astronomy? There are many unanswered questions for this project. 

California company wants to launch thousands of mirrors to space. A company called Reflect Orbital is proposing putting mirrors in space to reflect sunlight to the ground. Just imagine, You’ve worked a long shift, turned the lights out and settled into bed, when all of a sudden the sky outside your window lights up as if it’s daylight. This is what could happen if a US company has its way. Reflect Orbital is looking to send giant mirrors in space to “sell sunlight after dark.”  A proposed constellation of satellites has astronomers very worried. Unlike satellites that reflect sunlight and produce light pollution as an unfortunate by product, the ones by US startup Reflect Orbital would produce light pollution by design. The company promises to produce “sunlight on demand” with mirrors that beam sunlight down to Earth so solar farms can operate after sunset. It plans to start with an 18-meter (60-foot) test satellite named Earendil-1, which the company has applied to launch in 2026. It would eventually be followed by about 4,000 satellites in orbit by 2030, according to the latest reports. So, how bad would the light pollution be? And perhaps more importantly, can Reflect Orbital’s satellites even work as advertised?

It’s a plan that’s causing alarm among astronomers who are already concerned about the loss of the night sky due to satellite constellations, hundreds to thousands of satellites belonging to one company, most often providing internet services, and overall light pollution. But the California startup says their plan could help solve energy issues as well as provide lighting for situations like disaster rescue plans and more. Sunlight can be bounced off a wristwatch to produce a spot of light. In the same way you can bounce sunlight off a watch face to produce a spot of light, Reflect Orbital’s satellites would use mirrors to beam light onto a patch of Earth. But the scale involved is vastly different. Reflect Orbital’s satellites would orbit about 625 km (388 miles) above the ground. And they would eventually have mirrors 54 meters (177 feet) across. When you bounce light off your watch onto a nearby wall, the spot of light can be very bright. But if you bounce it onto a distant wall, the spot becomes larger, and dimmer. This is because the sun is not a point of light, but spans half a degree in angle in the sky. This means that at large distances, a beam of sunlight reflected off a flat mirror spreads out with an angle of half a degree. What does that mean in practice? Let’s take a satellite reflecting sunlight over a distance of roughly 800 km (500 miles). That’s because a 625-km-high (388-mile-high) satellite won’t always be directly overhead, but beaming the sunlight at an angle. The illuminated patch of ground would be at least 7 km (4.3 miles) across. Even a curved mirror or a lens can’t focus the sunlight into a tighter spot due to the distance and the half-degree angle of the sun in the sky.

Astronomers aren’t buying this idea. Aaron Boley, an astronomer and associate professor at the University of British Columbia, said there are "basic misunderstandings or willful misrepresentations" on the company's website. "They were talking about reducing light pollution by having this giant light from space. And it really seems like they're trying to suggest that because it's natural sunlight, it's not like pollution.” Would this reflected sunlight be bright or dim? Well, for a single 54-meter satellite, it will be 15,000 times fainter than the midday sun. But this is still far brighter than the full moon. Earth in space, with a large square foil reflector floating above it in orbit. Reflect Orbital says its space mirrors could provide solar farms with additional sunlight after the sun sets. The company, which filed a request with the US the Federal Communication Commission to launch its first satellite, EARENDIL-1, is proposing using the satellites to beam down reflected sunlight on specific locations, such as solar farms after the sun has set. Reflect Orbital has proposed a few different sizes of satellites, ranging from 10 x 10 metres, 18 x 18 metres and even 54 x 54 metres. But even at the top size, some experts say that in order to provide enough sunlight to a solar farm, thousands of satellites would be needed. “If you were to do the midday sun for instance, you would need a mirror that, from the ground, looked like it was the same size as the sun itself in the sky,” said Michael Brown, an associate professor in astronomy at Monash University in Melbourne, Australia. “That's many kilometres across when it's up in orbit. Now, no one's going to launch a mirror that's many kilometres across, so what they do is they launch multiple smaller mirrors. And Reflect Orbital’s talking about 54-metre-square mirrors. And to just produce 20 per cent of the midday sun, it looks like you need about 3,000, possibly more of these mirrors.”

Last year, Reflect Orbital’s founder Ben Nowack posted a short video that summarized a test with the “last thing to build before moving into space.” It was a reflector carried on a hot air balloon. In the test, a flat, square mirror roughly 2.5 meters (8.2 feet) across directs a beam of light down to solar panels and sensors. In one instance, the team measures 516 watts of light per square meter (11 sq ft) while the balloon is at a distance of 242 meters (794 feet). For comparison, the midday sun produces roughly 1,000 watts per square meter. So 516 watts per square meter is about half of that, which is enough to be useful. However, let’s scale the balloon test to space. As we noted earlier, if the satellites were 800 km (500 miles) from the area of interest, the reflector would need to be 6.5km by 6.5km, or 42 square km's (16 square miles). It’s not practical to build such a giant reflector, so the balloon test has some limitations. The idea of a space mirror isn’t a new one, which was first proposed in the 1920s. In 1993, Russia deployed Znamya 2, a space mirror 25 metres in diameter that ended up producing a five-kilometre bright spot. A few days later, it burned up over Canada. The US and the European Space Agency have also made such proposals, though none so far have come to fruition. Some say it's because it's not feasible. Reflect Orbital’s plan is “simple satellites in the right constellation shining on existing solar farms.” And their goal is only 200 watts per square meter, or 20% of the midday sun.

Can smaller satellites deliver? If a single 54-meter satellite is 15,000 times fainter than the midday sun, you would need 3,000 of them to achieve 20% of the midday sun. That’s a lot of satellites to illuminate one region. Another issue is that satellites at a 625-km (390 mile) altitude move at 7.5 km's per second (16,800 mph). So a satellite will be within 1,000 km (621 miles) of a given location for no more than 3.5 minutes. This means 3,000 satellites would give you a few minutes of illumination. To provide even an hour, you’d need thousands more. Reflect Orbital isn’t lacking ambition. In one interview, Nowack suggested 250,000 satellites in 600-km-high (370-mile-high) orbits. That’s more than all the currently cataloged satellites and large pieces of space junk put together. And yet, that vast constellation would deliver only 20% of the midday sun to no more than 80 locations at once, based on calculations above. In practice, even fewer locations would be illuminated due to cloudy weather. Additionally, given their altitude, the satellites could only deliver illumination to most locations near dusk and dawn, when the mirrors in low Earth orbit would be bathed in sunlight. Aware of this, Reflect Orbital plan for their constellation to encircle Earth above the day-night line in sun-synchronous orbits to keep them continuously in sunlight. A tall, narrow rocket launching on a pillar of fire, above billowing clouds of steam. Cheaper rockets have enabled the deployment of satellite constellations.

"With the proliferation of objects in orbit, there's a mentality that if you can do something from space, you should do something from space," Boley said. "And I think that is driving part of this idea." He explained that in order for the mirrors to work, the satellites would have to be on a polar orbit, which is like a ring moving from the south to north poles. That would take the satellites right over Canada. "There's this other issue of like shining light when you simply don't want it there … so because we have this sun-synchronous design, then we will be having these satellites just sweeping across Canada as twilight sweeps across Canada," he said. "And so Canada should be very vocal about that." In the early evening it doesn’t take long to spot satellites and space junk … and they’re not deliberately designed to be bright. With Reflect Orbital’s plan, even if just the test satellite works as planned, it will sometimes appear far brighter than the full moon. A constellation of such mirrors would be devastating to astronomy and dangerous to astronomers. To anyone looking through a telescope the surface of each mirror could be almost as bright as the surface of the sun, risking permanent eye damage. The light pollution will hinder everyone’s ability to see the cosmos, and light pollution is known to impact the daily rhythms of animals as well. Although Reflect Orbital aims to illuminate specific locations, the satellites’ beams would also sweep across Earth when moving from one location to the next. The night sky could be lit up with flashes of light brighter than the moon. The company did not reply to The Conversation about these concerns within deadline. However, it said that it plans to redirect sunlight in ways that are “brief, predictable and targeted,” avoiding observatories and sharing the locations of the satellites so scientists can plan their work.

Reflect Orbital has estimated the light produced by its mirrors would extend several kilometres across. There's concern over how that could impact not only people who don't want the light, but also wildlife. In a world of light pollution, this starry spot could become a top tourist destination. It remains to be seen whether Reflect Orbital’s project will get off the ground. The company may launch a test satellite, but it’s a long way from that to getting 250,000 enormous mirrors constantly circling Earth to keep some solar farms ticking over for a few extra hours a day. Still, it’s a project to watch. The consequences of success for astronomers, and anyone else who likes the night sky dark, would be dire. The number of satellites visible in the evening has skyrocketed in the recent past. John Barentine, founder of Dark Sky Consulting, said there's a lot that's unknown about Reflect Orbital's technical details. However, he added, information the company has disclosed suggests it will have unintended consequences. "These objects will appear like very bright stars in the sky moving slowly as seen from potentially hundreds of miles or kilometres away from the spot on the ground where the light appears," he said. "It's happening at a time when the world is dark. The expectation of [animal] biology is that the conditions will be dark around them. I worry a bit that if you are, say, a migratory bird, who we now know are navigating by the stars at some level, that this could be very disorienting." Then there are implications for observatories, both professional and amateur. "Reflect Orbital says we're definitely not going to light up your observatories, but if I have bright objects that look like stars moving through the sky far from where the beam is reaching the ground, if it's anywhere close to an observatory, that's still a problem," Barentine said. Brown, of Monash University, is also concerned about unintended radio interference from the satellites. Recently it was discovered that SpaceX's Starlink satellites are creating noise at radio observatories. But there's more that distresses him. "I'm also more concerned, oddly enough, I'd say from a sort of almost an aesthetic point of view. That I sort of like the sky being sort of this shared wilderness," he said. "If you go somewhere where it's nice and dark and look at the night sky and have these constant reminders of technology, I think that's a bit of a loss."