An American startup plans to provide “sunlight on demand” after dark. Can it work – and is it what we want?

The proposed satellite constellation has greatly concerned astronomers. Unlike satellites that reflect sunlight and produce light pollution as an unlucky byproduct, the satellites produced by the US start-up Orbit reflection by design would cause light pollution.

The company guarantees to produce “sunlight on demand” using mirrors that direct sunlight to Earth so that solar farms can do it operate after sunset.

It plans to start with an 18-meter test satellite called Earendil-1, for which the company has submitted an application start in 2026. Ultimately, by 2030, roughly 4,000 satellites might be in orbit, according to the latest reports.

How bad would the light pollution be? More importantly, can Reflect Orbital satellites even perform as advertised?

Reflecting sunlight

In the same way you’ll be able to reflect sunlight off a watch face to create a spot of sunshine, Reflect Orbital satellites use mirrors to send light onto a patch of Earth.

But the scale of this phenomenon is completely different. The Reflect Orbital satellites would orbit at an altitude of about 625 km above the earth and would eventually have mirrors Width 54 meters.

When you reflect the light from the watch onto a nearby wall, the spot of sunshine will be very vibrant. But if you reflect it on a far wall, the stain becomes larger – and darker.

This is because the Sun is not a point of sunshine, but extends across the sky at an angle of half a degree. This signifies that at large distances, the beam of sunlight reflected from a flat mirror diverges at an angle of half a degree.

What does this mean in practice? Let’s take a satellite reflecting sunlight to a distance of about 800 km – because a satellite 625 km high won’t at all times be directly overhead, but will emit sunlight at an angle. The illuminated patch of land can be at least 7 km wide.

Even a curved mirror or lens cannot focus sunlight into a narrower spot due to the distance and half-degree angle of the Sun in the sky.

Would this reflected sunlight be vibrant or dim? Well, in the case of a single 54-meter satellite, it might be 15,000 times fainter than the southern Sun, but will still be much brighter than the full Moon.

Balloon test

Last 12 months, Reflect Orbital founder Ben Nowack published a short video which summed up the “last thing to build before going to space” test. It was a searchlight transported in a hot air balloon.

In the test, a flat, square mirror about 2.5 meters in diameter directs a beam of sunshine down to the solar panels and sensors. In one case, the team measured 516 watts of sunshine per square meter when the balloon was 242 meters away.

For comparison, the midday sun produces about 1,000 watts per square meter. So 516 watts per square meter is about half of that, which is enough to be useful.

But let’s scale the balloon test to space. As we noted earlier, if the satellites were 800 km from the area of ​​interest, the reflector would have to be 6.5 km by 6.5 km – or 42 square kilometers. It is impractical to build such a gigantic reflector, so the balloon test has some limitations.

So what does Reflect Orbital plan to do?

Reflect Orbital’s plan calls for “simple satellites in the right constellation shining on existing solar farms.” And their goal is only 200 watts per square meter – 20% on noon Sunday.

Can smaller satellites provide a signal? If a single 54-meter satellite is 15,000 times fainter than the southern Sun, it would take 3,000 of them to reach 20% of the southern Sun. That’s a lot of satellites to illuminate one region.

Another point: satellites at an altitude of 625 km are moving at a speed of seven.5 km per second. Therefore, the satellite might be at a distance of 1000 km from a given location in not than 3.5 minutes.

This signifies that 3,000 satellites will provide several minutes of illumination. To provide even an hour, hundreds more can be needed.

Reflect Orbital has no shortage of ambition. In one of the interviews, Nowack suggested 250,000 satellites in orbits with a height of 600 km. It’s greater than that all currently cataloged satellites and large pieces of space junk combined.

And yet, according to our calculations above, this huge constellation would only deliver 20% of the southern Sun to not more than 80 locations at a time. In practice, due to the cloudy weather, even fewer locations can be illuminated.

Moreover, given their altitude, the satellites could only provide illumination to most places at dusk and dawn, when the mirrors in low Earth orbit can be bathed in sunlight. Aware of this, they Reflect the orbital plan for their constellation surrounding the Earth above the day-night line IN Sun-synchronous orbits so that they are continuously exposed to sunlight.

Bright lights

So are mirror satellites a practical way to produce inexpensive solar energy at night? Probably not. Could they cause devastating light pollution? Absolutely.

In the early evening, it doesn’t take long to spot satellites and space debris – and they are not intentionally designed to be vibrant. With the Reflect Orbital planeven if just the test satellite works as planned, it will sometimes appear much brighter than the full moon.

A constellation of such mirrors can be devastating to astronomy and dangerous to astronomers. For anyone searching through a telescope, the surface of each mirror will be almost as vibrant as the surface of the Sun, which is dangerous everlasting eye damage.

Light pollution will make it difficult for anyone to view space, and light pollution is also known to affect animals’ each day rhythms.

While Reflect Orbital’s purpose is to illuminate specific locations, the satellites’ beams may even sweep across the Earth as they move from one location to one other. The night sky will be lit up with flashes of sunshine brighter than the Moon.

The company didn’t respond to these concerns to The Conversation by deadline. However, he told Bloomberg this week plans to redirect sunlight in a “brief, predictable and targeted” way, avoiding observatories and sharing satellite locations so scientists can plan their work.

The consequences can be terrible

Time will tell whether the Reflect Orbital project might be implemented. The company may launch a test satellite, but there’s still a good distance to go to get 250,000 huge mirrors continuously orbiting the Earth so that some solar farms can run a few extra hours a day.

Still, it’s a project price watching. The consequences of success for astronomers – and anyone who enjoys dark night skies – can be dire.