Is Chengdu’s space mirror a green technology?

When I was a teenager I wrote a short story about a city that launched an artificial moon into space, made up of reflecting mirrors. In my story the mirrors could be configured into shapes, so it was usually round, but could be a smily face or a snowflake for special occasions. Everyone liked it until corporate sponsors were brought in to help pay for it, and then the moon was just a logo in the sky. Moonlight, brought to you by Coca Cola.

I was remined of this recently, as the Chinese city of Chengdu announced last month that it plans to install a space mirror to provide illumination at night. A series of three giant mirrors will reflect the light of the sun down over the city and a 50 square mile area around it. Apparently it will be brighter than your old-school natural moon, and cast enough light to replace street lights.

The hope is that Chengdu’s nightlight will save money as the city basks in a dusky twilight, at least when there’s a clear sky. With a population of over 14 million, Chengdu is a big city with a lighting bill to match, and they’re projecting a saving of £174 million a year in electricity and maintenance costs. I don’t know how much it costs to install a spacelight, but with those sorts of savings it shouldn’t take very long to pay for itself.

If you’re saving energy, you’re saving greenhouse gas emissions too, so does this qualify as a green technology? Once the emissions from creating it and blasting it into space are paid off, presumably it’s zero carbon light – and light accounts for 18% of the world’s electricity use.

So far the best solution for streetlights has been LEDs, and China has led the world in LED streetlights through its ‘cities of 10,000 lights’ programme. They deliver typical savings of 50-70%, which is great, especially when powered by renewable energy – but zero carbon is altogether better.

There may be consequences for nature of course, which is adapted to day and night cycles. We humans like to conquer darkness, but we’re part of nature and adapted to those cycles too. We mess with them at our peril, and light pollution affects human psychology as well as animal behaviour.

However, Chengdu’s spacelight won’t be as bright as normal streetlights. It would potentially be less disruptive to nature and sleep patterns than what the city already has. What’s more, despite the headlines all calling it an ‘artificial moon’, it will actually look like a bright star from the ground. Presumably that makes it less likely to tamper with creatures adapted to the lunar cycle.

Another downside is that if Chengdu prove it can be done, other cities might want one.  Some are already discussing mirrors to amplify solar power, to deflect sunlight and cool the earth, or – humans being humans – to create sun-powered weapons. However benign the nightlight might be, it may enable more dangerous applications later. Besides, we could do without a boom in space junk – the more we put into orbit, the higher the risk of collision or even a destructive chain-reaction.

Ultimately we’re going to have to wait and see. It’s an experiment, and it might not get any further than the Russian space mirror experiments in the 90s. If everything goes to plan we’ll see what it looks like by 2020, and China has promised to test their mirror in an uninhabited bit of desert first.

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