Artificial Moon of China – Numbers "Do not Add"

Artificial Moon of China – Numbers "Do not Add"

An "artificial moon" to illuminate a Chinese city at night – saving hundreds of millions in electricity. It looks like science fiction. And China's plan, says physicist Scott Manley, is just that.

A group of volunteers look through the door of the "Lunar Palace" – a lunar basic simulator

DW recently spoke with physicist and astronomer Scott Manley about plans for China's "artificial moon".

DW: What's wrong with the?

Scott Manley: The numbers they give us do not match. They talk about the spaceship 500 kilometers away [roughly 300 miles]which is good – it's a low Earth orbit. But then, they talk about providing light for an extended period. And the problem is that, at 500 km, satellites move very fast. If you see a satellite, it moves in the sky in a few minutes. Thus, they could only direct light on one point only a few minutes at a time. And that means that if you really want to light a city, you need several satellites, which must also be able to follow the ground position.

Has this already been done?

The Russians obviously tried to do it in the 1990s and they did not even adjust the angle of their lighting. They created a bright spot on the earth that was moving at seven kilometers per second. So you had to go after it if you wanted to get a steady light. Otherwise, you will only see a flash of light for a second. Geostationary orbit [36,000 kilometers above the Earth] is conventionally the magic distance to which it could stay on a single zone of the Earth.

about the space:

The first tests will take place in a desert, with the intention to enlighten Chengdu, 14 million inhabitants

Can not China put the artificial moon into geostationary orbit?

The problem is that as you move forward, you need to enlarge your mirror. As the reflected light scatters, there is a kind of fundamental physical limit: if you are in an orbit of 500 km, [a mirror of] 25 meters would give you something that is 10 times brighter than the moon. If you plan to cover 36,000 kilometers, you have to travel hundreds of meters. And if you followed the James Webb Space Telescope – NASA's next large space telescope – one of the big problems they face is to unfold their visor to zero in space. It's actually quite complicated to make a very compact object that can reliably deploy to zero g. especially since you can not really test it at zero g on Earth.

Other projects in Earth orbit:

Astronomers in Chengdu expected to leave province to observe stars without light pollution

But would the geostationary option work, at least in theory, to illuminate a medium-sized city?

You can not illuminate just a city. It would be a fairly large province. If you have a 600-meter mirror, of course … There's this sci-fi film that lets you do the "Archimedes Light Weapon", where you focus the sun on a target. Fortunately, you can not do it from a geostationary orbit to a target on the Earth, unless your mirror is really huge – we're talking about hundreds of kilometers or more.

But in geostationary orbit, you also have the other problem that your spaceship will reflect the sun. And we think that the sun is only light. But light exerts a pressure that will act as a force. This means that the rays essentially push your spaceship. And that will change the orbit over time. Thus, the spacecraft should not only reflect the sun. He should also make adjustments for the disturbances that the sun would cause to keep him in that orbit.

So, "China Daily" is he cheated? Would you say that?

I think they have just been very excited. I think that realistically, they will test it in low Earth orbit. They then claim that, if they could permanently, they could save hundreds of millions of dollars in public lighting. But that would require several satellites and very carefully coordinated orbits, all coordinating and ensuring continuous illumination. And I do not think 500 kilometers is a good altitude for that. I think that intermediate orbits could also be used. You can also place it on a synchronous polar solar orbit that flies over the city at the right time.

And of course, even if you find yourself in a situation where you could make it as bright as the moon every night, it would disrupt biological processes on Earth. There are animals that would see this thing and disturb their different monthly rhythms, I suppose. So, you know, there are many things to consider when doing these big projects.

Will the artificial moon change the life of this red panda in danger in Chengdu?

But this is achievable at a certain level.

This is, but not as described in their article.

physicist and astronomer training, is best known online as a "rocket specialist on the Internet".

The interview was modified for its length and clarity.

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