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Why China's artificial moon probably does not work



Going outside on a moonlit night means pushing back the darkness. The reflected sunlight from our natural satellite during an almost full moon is enough to limit the night landscape to silver and even allow human eyes to penetrate into the darkness. But we can always do better, right? If a moon is good, two are certainly even better.

At least that's what a Chinese researcher thinks. Wu Chunfeng, head of the Tian Fu New Area Science Society, wants to use a satellite such as an artificial moon, which reflects sunlight into the Earth's target areas at night. The reflector would circle over a city and provide sufficient lighting to replace the lights on the floor with a steady glow and possibly save electricity costs.

Brighten the Night

He imagines a shining satellite unfolding in space about 300 miles above the ground and oriented toward cities on the ground. One would be enough to illuminate about 5o square miles, he says after China Daily and several works in concert could brighten up to 4000 square miles. Wu says the first one should be put into operation in 2020 and three more in 2022, although the details of the project are largely unknown.

The plan is not so good, according to satellite experts. Given the limited data available, the satellite would probably never work, says Ryan Russell, an associate professor of aerospace engineering at the University of Texas at Austin.

The biggest mistake? A satellite that flies low enough to deliver so much light would not be able to stay in one place.

"Your claim to 1

LEO at [300 miles] must be a typo or misinformed speaker," Russell says in an email. "The article I read suggested that you could levitate a satellite over a certain city, which of course is not possible."

Satellites that remain above a fixed point on Earth, which is called a geostationary orbit, sit much further away: about 38,000 miles. At that distance, the reflective surface would have to be massive enough to provide enough light for people to see back to Earth. At a distance of only 300 miles, the moon circled the earth at thousands of miles per hour, emitting its light to some place for only a fraction of a second.

They could hold an artificial moon with rocket engines in place, says Iain Boyd, a professor of aerospace engineering at the University of Michigan, but that would consume fuel, which would increase costs and require constant refueling.

A constellation of satellites orbiting the earth would be necessary to hold all the lights at night, buying off mutually reflective duties as they passed them. And even then, fuel is needed to counteract the low atmospheric resistance that exists even in low orbits above the earth. The International Space Station, for example, orbits about 250 miles and must constantly be returned to orbit as it slows down due to air resistance.

The cost of starting and refueling multiple satellites would probably far exceed the power savings, at least for the moment.

Turn off the lights

It also raises the question of whether we even want a city-wide night light. Some cities around the world are already trying to stem light pollution, making their nights darker and brighter. Excessive nocturnal light disturbs the activities of nocturnal animals, blocks the stars and could even disrupt our circadian rhythms and affect our health.

If we really need better lighting solutions, it may be better to focus on more terrestrial options, Russell says.

"It's a very complicated solution that affects everyone on a simple problem that affects some, it's light pollution on steroids," he says. "And they illuminate the entire area, while street lights only illuminate the streets that need to be lit. Do you imagine whole generations of people living in the same urban areas and never seeing the stars at night?"


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