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A North American company plans to provide “sunlight on demand” after dark. It might work, but do we really want it? THE satellite constellation proposed by Reflect Orbital It’s making astronomers worried.
Unlike satellites that reflect sunlight and produce light pollution as an unwanted byproduct, those from the US company Reflect Orbital would produce light pollution by design.
The company promises generate “sunlight on demand” with mirrors that project sunlight to Earthallowing solar plants to operate after sunset.
According to , the company plans to start with an 18-meter test satellite, called Earendendi-1whose launch authorization in 2026 has already been requested by the company. Then, according to the most recent reports, this would be followed by around 4,000 satellites in orbit by 2030.
But how serious would it be? light pollution? And, perhaps most importantly, the satellites of Reflect Orbital Will they even be able to work as advertised?
Reflect sunlight
In the same way that sunlight can be reflected off a clock face to produce a spot of light, Earth’s satellites Reflect Orbital they would use mirrors to project light onto an area of the Earth.
But the scale involved is vastly different. The satellites of Reflect Orbital by orbitariam about 625 km above the ground and would eventually have mirrors 54 meters in diameter.
When light from the clock is reflected onto a nearby wall, the point of light may be very bright. But if it reflects off a distant wall, the dot becomes larger – and fainter.
This is due to the fact that the Sun is not a point of light, but rather covers half a degree of angle in the sky. This means that, at great distances, a beam of sunlight reflected from a flat mirror spreads out at an angle of half a degree.
What does this mean in practice? Let’s take a satellite that reflects sunlight at a distance of about 800 km – because a satellite at an altitude of 625 km will not always be directly overhead, but will project sunlight at a certain angle. THE illuminated area on the ground would be at least 7 km in diameter.
Even a curved mirror or lens would not be able to focus sunlight into a tighter spot, due to the Sun’s distance and half-degree angle in the sky.
Would the reflected sunlight be bright or dim? Well, for a single 54 meter satellite, it would be 15,000 times weaker than the Sun at noonbut still, much brighter than the full moon.
The balloon test
Last year, the founder of Reflect Orbital, Ben Nowackpublished a brief video that summarized a test with “the last thing to build before going into space”. It was a reflector transported by a hot air balloon.
In the test, a flat, square mirror measuring about 2.5 meters on a side directs a beam of light towards solar panels and sensors. In one of the measurements, the team recorded 516 watts of light per square meter, with the balloon at a distance of 242 meters.
For comparison, the Sun at midday produces about 1,000 watts per square meter. So 516 watts per square meter corresponds to about half, which is enough to be useful.
However, we will scale the balloon test into space. As we have already noted, if the satellites were 800 km from the area of interest, the reflector would have to measure 6.5 km by 6.5 km – 42 square kilometers. It is not practical to build such a gigantic reflector, so the Balloon test has obvious limitations.
So what is Reflect Orbital planning?
The plan of Reflect Orbital and: “simple satellites in the right constellation illuminating existing solar plants”. And your goal is just 200 watts per square meter – 20% of the sun at noon.
Could smaller satellites achieve this? If a single 54-meter satellite is 15,000 times fainter than the Sun at midday, it would take 3,000 satellites to reach 20% of the midday sunlight. That’s a huge number of satellites to illuminate just one region.
Another problem: satellites at an altitude of 625 km move at 7.5 kilometers per second. Thus, a satellite will be less than 1,000 km from a given location for a maximum of 3.5 minutes.
This means that 3,000 satellites would provide just a few minutes of illumination. To provide a full hour, many thousands more would be needed..
A Reflect Orbital does not lack ambition. In an interview, Nowack suggested 250,000 satellites in orbits at 600 km altitude. That’s more than all the satellites and large space debris currently cataloged combined.
And yet, this vast constellation would provide just 20% of midday sunlight to no more than 80 locations simultaneously, based on the calculations above. In practice, even fewer locations would be illuminated due to cloudiness.
Furthermore, given their altitude, satellites could only provide lighting to most locations near dusk and dawnwhen mirrors in low Earth orbit would still be bathed in sunlight.
Distinct customer, Reflect Orbital plan that your constellation circle the Earth above the day-night line, in Sun-synchronous orbits, so that they remain continually in sunlight.
Bright lights
So are satellites with mirrors a practical way to produce cheap solar energy at night? Probably not, experts consider Michael J. I. Brown e Matthew Kenworthyin The Conversation article.
Could they cause devastating light pollution? “Absolutely”, they say.
In the early evening, it’s not difficult to spot satellites and space debris – and they’re not even designed to be bright. With the plan of Reflect Orbitaleven if just the test satellite works as expected, it will sometimes be much brighter than the full Moon.
A constellation of such mirrors would be devastating for astronomy and dangerous for astronomers. For anyone observing through a telescope, the surface of each mirror could be almost as bright as that of the Sun, putting permanent eye damage at risk.
Light pollution will harm everyone’s ability to see the cosmos, and light pollution is known to artificial light affects animals’ daily rhythms.
Although the Reflect Orbital intended to illuminate specific locations, the satellites’ beams would also sweep across the Earth as they move from one location to another. The night sky could be illuminated by flashes of light brighter than the Moon.
Last week, the company told the company that it plans to redirect sunlight from “brief, predictable and targeted” formsavoiding observatories and sharing satellite locations so scientists can plan their work.
The consequences would be dire
It remains to be seen whether the project Reflect Orbital will actually come out of the paper. The company may launch a test satellite, but it is a long way to go before it has 250,000 huge mirrors constantly orbiting the Earth, keeping some solar plants running for a few more hours a day.
Still, it’s a project to follow. “The consequences of success – for astronomers and anyone who enjoys the dark night sky – would be dire,” write Michael JI Brown and Matthew Kenworthy.
