Originally published 2018-11-05.
In October 2018, Wu Chunfeng, head of the Tian Fu New Area Science Society in Chengdu, told China Daily that the city planned to put an "artificial moon" into orbit by 2020. The idea was a satellite carrying large reflective panels that would bounce sunlight onto part of Chengdu at night, with the aim of replacing some street lighting and cutting electricity bills. If the first satellite worked, three more were to follow in 2022.
It was a local proposal, not a project announced by China's national space agency, and there is no public evidence that the satellite was ever launched. Here is what was promised, how the technology would work, and why ideas like this have proved so hard to deliver.
What Chengdu announced
The details came from Wu's interview with China Daily and reports that followed:
- Orbit: about 500 km above Earth, compared with roughly 380,000 km for the real Moon.
- Launch site: the Xichang Satellite Launch Center in Sichuan province.
- Brightness: described as up to eight times brighter than the Moon, though Wu said people on the ground would perceive it at about one-fifth of a normal streetlight.
- Accuracy: the light could reportedly be aimed to within a few dozen metres.
- Savings: lighting 50 square kilometres of Chengdu was projected to save about 1.2 billion yuan (around $170 million) a year in electricity.
- Later phase: three satellites working together could, it was claimed, light 3,600 to 6,400 square kilometres.
According to the same report, the Harbin Institute of Technology and China Aerospace Science and Industry Corporation had reviewed the concept and approved it for trial and demonstration. Wu also said the satellite could help emergency teams by lighting areas hit by blackouts or natural disasters, and that it would be tested first over uninhabited desert so it would not disturb people or ground-based astronomy.
How a "man-made moon" would work
Despite the name, the plan was not to build a glowing object. The satellite would act like a mirror. Panels with a reflective coating, angled a bit like solar-panel wings, would sit high enough to stay in sunshine after dusk on the ground, and would redirect that sunlight down onto the darkened city below.
Wu was clear that residents should not expect to look up and see a second giant moon. To the naked eye the satellite would look like a bright star, and the light on the ground would be a dim glow rather than daylight. He also said it would not light up the whole night sky.
There is a physical challenge here. A satellite at 500 km does not hover over one city; at that height it circles the Earth in about an hour and a half. Keeping a beam of light on Chengdu would require either many satellites in sequence or a very different orbit, and the published reports did not explain how this would be solved.
Russia tried it first
The idea is older than Chengdu's plan. In the 1990s Russia's Znamya experiments tested space mirrors launched from the Mir space station.
Znamya 2, a 20-metre reflector, was unfolded on 4 February 1993. It worked: a spot of light about 5 km wide, roughly as bright as a full moon, swept across Europe from southern France to western Russia at around 8 km per second, before the mirror was de-orbited a few hours later. A larger 25-metre version, Znamya 2.5, followed in February 1999 and was meant to cast a brighter, 7 km spot, but it snagged on an antenna on its spacecraft, tore, and was abandoned. Plans for even larger mirrors were dropped.
Those tests showed that sunlight can be reflected from orbit. They also showed how small, brief and fragile the result is compared with what a city's lighting network does every night.
The concerns scientists raised
When the plan was reported, critics pointed to light pollution. Even a faint extra glow could interfere with astronomical observation, and a bright moving point in the sky is exactly what observatories try to avoid. Others worried about wildlife and people, since nocturnal animals and human sleep both depend on natural cycles of darkness.
Supporters played this down. Kang Weimin of the Harbin Institute of Technology's School of Aerospace argued that the glow would be too weak to turn night into day, and closer to dusk than to daylight.
Practical questions were left unanswered too. Clouds would block the light on overcast nights. The cost of building, launching and replacing satellites was not published. And a beam that can cover tens of square kilometres cannot light the inside of an underpass or a narrow alley the way a streetlight can.
What actually happened
The 2020 launch date passed without any confirmed launch, and the three-satellite phase planned for 2022 did not materialise either. The project never appears to have moved from announcement to an identifiable mission, and no measured results have been published. The fairest summary is that Chengdu's artificial moon remained a proposal.
That does not make the story worthless. It is a good example of how a bold local announcement can travel the world as if it were a done deal. Headlines at the time said "China will launch" an artificial moon; the more accurate phrase would have been "a Chengdu science group says it hopes to".
Cheaper ways to cut lighting costs
The goal behind the plan, spending less energy on street lighting, is a real one, and cities have found down-to-earth ways to do it:
- LED streetlights use much less electricity than older sodium lamps and last longer.
- Smart controls dim lights on empty streets late at night and brighten them when sensors detect people or cars.
- Shielded fittings send light down onto the road instead of up into the sky, saving energy and reducing light pollution at the same time.
None of these makes headlines like a second moon, but they work on cloudy nights, in narrow streets and on a city budget.
Sources: China Daily: Man-made moon to shed light on Chengdu in 2020; Smithsonian Magazine: Chinese city wants to launch fake moon; Wikipedia: Znamya (satellite).
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