The night skies might soon have company: Chinese scientists are planning to launch an artificial moon into orbit by 2020 to illuminate city streets after dark.

Scientists are hoping to hang the man-made moon above the city of Chengdu, the capital of China’s southwestern Sichuan province, according to a report in Chinese state media. The imitation celestial body — essentially an illuminated satellite — will bear a reflective coating to cast sunlight back to Earth, where it will supplement streetlights at night.

Scientists estimated that it could be eight times more luminous than the actual, original moon. It will also orbit much closer to Earth; about 500 km (310 miles) away, compared to the moon’s 380,000 km (236,000 miles).

But the ambitious plan still wouldn’t “light up the entire night sky,” Wu Chunfeng, chief of the Tian Fu New Area Science Society, told China Daily. “Its expected brightness, in the eyes of humans, is around one-fifth of normal streetlights.”

http://time.com/5429288/china-chengdu-artificial-moon/

There are some problems here, and I don’t know whether the issue is that the chief of the Tian Fu New Area Science Society doesn’t know about science, or the Time correspondent didn’t understand the material, or there was a mistranslation.

1/
You can’t “hang” a satellite over a city at an altitude of 500 km. 500 km is low earth orbit. This thing will be orbiting the earth about 14 times a day. You’d need an array of these objects if you wanted Chengdu to have an “artificial moon” in the sky all the time or even most of the time.

2/
You’ll need more than a satellite with a reflective coating. You’ll need a flat, or flattish, mirror.

3/
You’re never going to be able to illuminate Chengdu with a space mirror at 500 km altitude in the dead of night. This is just basic geometry. It will give you a few hours after sunset and before sunrise but in the middle of the night, it can’t be done.

So let’s assume that there was just some miscommunication, and the actual plan is to use an array of space mirrors to increase the hours of illumination in Chengdu.

Other outlets indicate that they are seeking to illuminate an area 80 km across. They’d require a slightly convex mirror for that purpose.

They say “eight times” brighter than the original moon. Let’s assume they mean full moon. The sun is 400000 times brighter to us than the full moon so the brightness of a Chengdu space mirror will be about 1/50000 as bright as the sun. If the area of illumination is 80 km across, then the mirror will need to be about 350 metres across (assuming perfect reflection etc).

Certainly, this would be the biggest thing ever put in space, in terms of length or area. The ISS for instance is about 100 metres across. On the other hand this need not be a very complex structure. You would need a frame and a thin membrane mirror that could be kept in the appropriate shape, you’d need rocketry for frequent burns (since this thing would lose altitude quickly, due to high area to mass ratio) to maintain altitude, and you’d need big gyros or small rockets to control the attitude so that the reflection went to Chengdu. You’d go through quite a lot of fuel maintaining altitude so you’d probably have service missions to refuel, rather than launch it with all the fuel it would need for the full time in service.

And of course as I said you’d need several of these. Probably twelve at a bare minimum if you wanted to ensure there was always at least one in Chengdu’s sky. Even if we were to assume that each one of these things, much bigger than the ISS, only cost as much as the ISS to launch and construct, then you would honestly not get much change out of a trillion dollars for this program.

It’s being proposed as an alternative to street lighting but for a lot of the time, it won’t be great for lighting streets in a city with many tall buildings. A space mirror low in the sky would still leave many areas unilluminated (much as the full moon does when it is low in the sky). Only went it is high in the sky will it serve this purpose.

Now, I don’t know what it costs to light streets in Chengdu currently. The total street lighting cost in Australia is around $125 million per year. Chengdu is a big city, with a population about half of all Australia … but it’s total street length is comparable to that of Sydney. Any BOTE calc is going to indicate that lighting Chengdu, for the next hundred years, is going to cost a few billion dollars.

So yeah … something doesn’t add up.

Sounds like a load of bullshit.

Be cheaper just to fit a few large cargo aircraft with lithium batteries and banks of LED lights and get them to fly a circle pattern around the city. They can be plugged in to recharge during the day using vast solar panels.

I mean it is probably cheaper to just use streetlighting … like lamps on poles.

There was a Russian space mirror project called Znamya in 1992. It was a small mirror compared to that which would be required for the Chengdu project: about 20 metres across, so total area about 1/300 that need for Chengdu, mission mass perhaps 1/1000 (remembering that although the membrane mass will be proportional to area, the structural elements will need to scale as a volume).

There was no attempt to control the reflection point, so the reflected light point just raced across Europe. Znamya deorbited within a few hours due to drag.

cross out it’s
replace with its

I was wondering about this.

I was thinking, if you’re going to put a mirror into geostationary orbit at about 36,000 km away, and have it reflect a useful amount of light that is going to have to be one big-arse mirror.

And if you put mirrors into low-Earth orbit at 500 km, then how long will they last before atmospheric drag pulls them out of orbit? Not terribly long, methinks, hardly justifying the expense.

wont somebody think of the telescopists?

Perhaps this is a Chinese reaction to western rat bag science.

captain_spalding said:

I was wondering about this.

I was thinking, if you’re going to put a mirror into geostationary orbit at about 36,000 km away, and have it reflect a useful amount of light that is going to have to be one big-arse mirror.

And if you put mirrors into low-Earth orbit at 500 km, then how long will they last before atmospheric drag pulls them out of orbit? Not terribly long, methinks, hardly justifying the expense.

Theoretically, a slightly concave mirror in geostationary orbit could focus light onto a small area on the surface. This would remove some of the problems I mentioned before (drag, the requirement for many satellites, the impossibility of using it in the dead of night).

On the other hand, it’s further away and harder to refuel, and it will still need periodic attitude corrections (altitude correction won’t be an issue). I can’t speak to the practicality of manufacturing space mirrors precisely enough for this purpose.

But yeah in a lot of ways this is more appealing than Chunfeng’s 500 km idea.

Illuminating city streets is just a cover story, it’s obviously a stage in a cunning oriental plan of world domination by these inscrutable celestials.

AwesomeO said:

Illuminating city streets is just a cover story, it’s obviously a stage in a cunning oriental plan of world domination by these inscrutable celestials.

I’ll give you a partial payment for the apt double meaning of celestials.

dv said:

AwesomeO said:

Illuminating city streets is just a cover story, it’s obviously a stage in a cunning oriental plan of world domination by these inscrutable celestials.

I’ll give you a partial payment for the apt double meaning of celestials.

I’ll let you have it, interested to hear.

AwesomeO said:

dv said:

AwesomeO said:

Illuminating city streets is just a cover story, it’s obviously a stage in a cunning oriental plan of world domination by these inscrutable celestials.

I’ll give you a partial payment for the apt double meaning of celestials.

I’ll let you have it, interested to hear.

Celestial Empire or Tianchao a name used to refer to China.

dv said:

The night skies might soon have company: Chinese scientists are planning to launch an artificial moon into orbit by 2020 to illuminate city streets after dark.

Scientists are hoping to hang the man-made moon above the city of Chengdu, the capital of China’s southwestern Sichuan province, according to a report in Chinese state media. The imitation celestial body — essentially an illuminated satellite — will bear a reflective coating to cast sunlight back to Earth, where it will supplement streetlights at night.

Scientists estimated that it could be eight times more luminous than the actual, original moon. It will also orbit much closer to Earth; about 500 km (310 miles) away, compared to the moon’s 380,000 km (236,000 miles).

But the ambitious plan still wouldn’t “light up the entire night sky,” Wu Chunfeng, chief of the Tian Fu New Area Science Society, told China Daily. “Its expected brightness, in the eyes of humans, is around one-fifth of normal streetlights.”

http://time.com/5429288/china-chengdu-artificial-moon/

There are some problems here, and I don’t know whether the issue is that the chief of the Tian Fu New Area Science Society doesn’t know about science, or the Time correspondent didn’t understand the material, or there was a mistranslation.

1/
You can’t “hang” a satellite over a city at an altitude of 500 km. 500 km is low earth orbit. This thing will be orbiting the earth about 14 times a day. You’d need an array of these objects if you wanted Chengdu to have an “artificial moon” in the sky all the time or even most of the time.

2/
You’ll need more than a satellite with a reflective coating. You’ll need a flat, or flattish, mirror.

3/
You’re never going to be able to illuminate Chengdu with a space mirror at 500 km altitude in the dead of night. This is just basic geometry. It will give you a few hours after sunset and before sunrise but in the middle of the night, it can’t be done.

So let’s assume that there was just some miscommunication, and the actual plan is to use an array of space mirrors to increase the hours of illumination in Chengdu.

Other outlets indicate that they are seeking to illuminate an area 80 km across. They’d require a slightly convex mirror for that purpose.

They say “eight times” brighter than the original moon. Let’s assume they mean full moon. The sun is 400000 times brighter to us than the full moon so the brightness of a Chengdu space mirror will be about 1/50000 as bright as the sun. If the area of illumination is 80 km across, then the mirror will need to be about 350 metres across (assuming perfect reflection etc).

Certainly, this would be the biggest thing ever put in space, in terms of length or area. The ISS for instance is about 100 metres across. On the other hand this need not be a very complex structure. You would need a frame and a thin membrane mirror that could be kept in the appropriate shape, you’d need rocketry for frequent burns (since this thing would lose altitude quickly, due to high area to mass ratio) to maintain altitude, and you’d need big gyros or small rockets to control the attitude so that the reflection went to Chengdu. You’d go through quite a lot of fuel maintaining altitude so you’d probably have service missions to refuel, rather than launch it with all the fuel it would need for the full time in service.

And of course as I said you’d need several of these. Probably twelve at a bare minimum if you wanted to ensure there was always at least one in Chengdu’s sky. Even if we were to assume that each one of these things, much bigger than the ISS, only cost as much as the ISS to launch and construct, then you would honestly not get much change out of a trillion dollars for this program.

It’s being proposed as an alternative to street lighting but for a lot of the time, it won’t be great for lighting streets in a city with many tall buildings. A space mirror low in the sky would still leave many areas unilluminated (much as the full moon does when it is low in the sky). Only went it is high in the sky will it serve this purpose.

Now, I don’t know what it costs to light streets in Chengdu currently. The total street lighting cost in Australia is around $125 million per year. Chengdu is a big city, with a population about half of all Australia … but it’s total street length is comparable to that of Sydney. Any BOTE calc is going to indicate that lighting Chengdu, for the next hundred years, is going to cost a few billion dollars.

So yeah … something doesn’t add up.

Let’s see if together we can work out whether this actually means something or whether it’s the Chinese equivalent of an April fools day joke.

Start by looking for publications (in any language) by the China National Space Administration (CNSA) 国家航天局

28/8/2018 – “China develops large aperture optical mirror with high accuracy” – “China has developed a high accuracy four-meter-aperture optical mirror, an important tool for deep space and astronomical observation. Developed by Changchun Institute of Optics, Fine Mechanics, and Physics of the Chinese Academy of Sciences, the silicon carbide aspheric optical mirror measures 1.6 tonnes”.

That’s their latest press release. May or may not be relevant.

From wikipedia:

“Plans currently include a permanent Chinese space station in 2020.” “The Chinese space station 基本型空间站 will be a modular design with an eventual weight of around 60 tons, to be completed sometime before 2020. The first section, designated Tiangong 3, will weigh 22 tons and be 18.1 metres long. Additional modules will be connected over several missions to build the space station.” “The Modular Space Station Core Module would be called Tianhe 天和.

That would make the Chinese space station the second brightest manmade object in the sky after the ISS. Again, may or may not be relevant.

Let’s google “国家航天局 2020” and see what pops up.

First hit,

“The China Space Station will be built into an international strategic technology infrastructure to provide services to the One Belt, One Road participating countries.”

“the PALAPA-N1 communication satellite will be delivered to Indonesian customers in the first half of 2020. The Chinese company will provide a package of products and services including satellite, launch service, ground system, insurance and financing support.”

“Ye Peijian speaks about the lunar exploration project: after the 2020, he built a scientific research station on the moon.”

Hmm, nothing relevant on those last two. Try twitter. I don’t see anything relevant there from CNSA.

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

dv said:

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

Someone’s been doing some calculating :)

dv said:

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

Um, no. Can do very much better than that with a curved mirror. The size of the dot on Earth is only limited by the atmospheric turbulence, mirror diameter and mirror fabrication accuracy.

mollwollfumble said:

dv said:

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

Um, no. Can do very much better than that with a curved mirror. The size of the dot on Earth is only limited by the atmospheric turbulence, mirror diameter and mirror fabrication accuracy.

Mmm I’m afraid not, even with a curved mirror. Any tiny surface of that mirror at geostationary will make an image of the sun with 300 km diameter on the earth’s surface, and any reflection from a curved mirror will also be a superposition of such images.

I don’t know about the pollution situation in Chengdu; would a relatively dim object like this even be seen in the night sky? I’ve heard reports of pollution in some Chinese cities being so bad that the sun in broad daylight is only a fuzzy blob.

Divine Angel said:

I don’t know about the pollution situation in Chengdu; would a relatively dim object like this even be seen in the night sky? I’ve heard reports of pollution in some Chinese cities being so bad that the sun in broad daylight is only a fuzzy blob.

rofl good point

dv said:

Divine Angel said:

I don’t know about the pollution situation in Chengdu; would a relatively dim object like this even be seen in the night sky? I’ve heard reports of pollution in some Chinese cities being so bad that the sun in broad daylight is only a fuzzy blob.

rofl good point

https://www.youtube.com/watch?v=3A3alSCUCRI

It’s not as bad as some places, but it’s pretty bad.

They’re dreamin’, if they think a few lumens from a big bit of tinfoil in the sky is goingto help.

‘Afghans vote amid chaos and corruption’ – ABC News

Who doesn’t?

….aaaand wrong thread again.

dv said:

mollwollfumble said:

dv said:

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

Um, no. Can do very much better than that with a curved mirror. The size of the dot on Earth is only limited by the atmospheric turbulence, mirror diameter and mirror fabrication accuracy.

Mmm I’m afraid not, even with a curved mirror. Any tiny surface of that mirror at geostationary will make an image of the sun with 300 km diameter on the earth’s surface, and any reflection from a curved mirror will also be a superposition of such images.

Perhaps you’re right. I’ll check the calcs. Looks like you’re right, I wonder if there’s a way around that (other than using a laser). A curved mirror can make the centre brighter and the edges duller. Can the f-stop be changed? What about a metamaterial with negative refractive index or a phased array reflector?

mollwollfumble said:

dv said:

mollwollfumble said:

Um, no. Can do very much better than that with a curved mirror. The size of the dot on Earth is only limited by the atmospheric turbulence, mirror diameter and mirror fabrication accuracy.

Mmm I’m afraid not, even with a curved mirror. Any tiny surface of that mirror at geostationary will make an image of the sun with 300 km diameter on the earth’s surface, and any reflection from a curved mirror will also be a superposition of such images.

Perhaps you’re right. I’ll check the calcs. Looks like you’re right, I wonder if there’s a way around that (other than using a laser). A curved mirror can make the centre brighter and the edges duller. Can the f-stop be changed? What about a metamaterial with negative refractive index or a phased array reflector?

Looks like a few more inmates for the Re-education Center.

Zao already tried this another day, before he died.

SCIENCE said:

Zao already tried this another day, before he died.

Very droll.

dv said:

I mean it is probably cheaper to just use streetlighting … like lamps on poles.

oh.. boring!!

dv said:

Then again, no way to get around the fact of the sun not being a point source. It takes up 0.5 degrees of sky, so the smallest region you could illuminate with a reflector in geostationary orbit would be 300 km across.

Following that thought through. The smallest region of Earth you could illuminate with a reflector in geostationary orbit aimed at Alpha Centauri A would be 1.2 metres. What if you filled that area with CCDs? High resolution image, yes.

For a few other stars.
R Doradus >= 9 metres.
Betelgeuse >= 8.5 metres
Alphard = 1.6 metres
Canopus = 1.0 metres
Sirius = 1.0 metres
Proxima Centauri = 0.17 metres.

Or within our solar system
Venus = 1.7 km to 11.5 km
Jupiter = 5.2 km to 8.7 km
Neptune = 400 metres
Pluto = 10 to 19 metres
Eris = 6 to 15 metres

So if you want to light a city use Venus or Jupiter.

If you want the size to do good astronomy, try any of the above.

Have the Chinese said how big they will will be ?

without reading the entire thread. what risk of the moon falling out of orbit and plummeting back to earth and causing or not causing any damage is there?

monkey skipper said:

without reading the entire thread. what risk of the moon falling out of orbit and plummeting back to earth and causing or not causing any damage is there?

There is a risk, they will need to keep boosting it back when it falls.

There are still no details on its mirror diameter.

It will orbit at 500 kilometres above the Earth and light up an area with a diameter of 10 to 80 kilometres.

There are some interesting comments about its orbit here.

http://en.people.cn/n3/2018/1016/c90000-9508748.html

Having artificial light at night, might confuse the birds and wildlife.

Tau.Neutrino said:

Having artificial light at night, might confuse the birds and wildlife.

Like moths to a streetlight or an eclipse sending the birds home to roost…

Having an artificial moon means there will be more werewolves, you Mark my words.

Divine Angel said:

Tau.Neutrino said:

Having artificial light at night, might confuse the birds and wildlife.

Like moths to a streetlight or an eclipse sending the birds home to roost…

When I was at uni, we were involved in lighting up salmon pens so we could trick the salmon into being in season all year round. by changing the day length with artificial lighting, we could induce a breeding season, shorten it or prevent it completely

monkey skipper said:

without reading the entire thread. what risk of the moon falling out of orbit and plummeting back to earth and causing or not causing any damage is there?

Negligible.

Stumpy_seahorse said:

Divine Angel said:

Tau.Neutrino said:

Having artificial light at night, might confuse the birds and wildlife.

Like moths to a streetlight or an eclipse sending the birds home to roost…

When I was at uni, we were involved in lighting up salmon pens so we could trick the salmon into being in season all year round. by changing the day length with artificial lighting, we could induce a breeding season, shorten it or prevent it completely

I think that’s also how they trick caged chickens into laying eggs.

Divine Angel said:

Stumpy_seahorse said:

Divine Angel said:

Like moths to a streetlight or an eclipse sending the birds home to roost…

When I was at uni, we were involved in lighting up salmon pens so we could trick the salmon into being in season all year round. by changing the day length with artificial lighting, we could induce a breeding season, shorten it or prevent it completely

I think that’s also how they trick caged chickens into laying eggs.

Yeah and the Marijuana growers use day length changes to make their plants flower.

“Tian Fu New Area Science Society,”

Looking up Wikipedia, it’s actually Chengdu Tianfu New Area

The planning scope of Tianfu New Area includes the southern part of Chengdu High-tech Zone, Longquanyi District, Shuangliu County, Xinjin County, Jianyang City, Pengshan County of Meishan City and Renshou County. It involves in total 3 cities, 7 counties (city, district) and 37 towns and villages . The total area is planned to cover 1,578 km (981 mi).

天府新区

It is understood that the first 84 projects of Chengdu Tianfu New Area include 51 industry projects with the investment of 169.5 billion RMB (including 27 industrial projects with investment of 82.35 billion RMB and 24 service projects with investment of 87.15 billion RMB), 29 infrastructure projects with investment of 43.4 billion RMB, and 4 ecology projects with investment of 1.5 billion RMB.

One major project in the Tianfu New Area is the construction of the New Century Global Centre(complete), Chengdu Tianfu International Airport and the Chengdu Contemporary Arts Centre.

Sichuan Tianfu district plan in 2010, the future population projections 500 million (people?), involving Chengdu Tianfu District Chengdu straight District , Chengdu Hi-tech Zone , Shuangliu District , Longquan District , Xinjin County , Jianyang City , Meishan City of Peng mountain , Renshou County , The planned area is 1578 square kilometers.

As of 2017, Sichuan Tianfu New District has generated a total of 784.33 billion yuan of GDP, an average annual growth rate of 8.7%; accumulated fixed assets investment of 653.41 billion yuan, an average annual growth of 18.5%.

Chengdu Science City will be established by 2020.

Construction of Tianfu New Area was approved in May 2011. The government offices there started to operate in Dec 2013.

Why can’t we build like that in Australia?

Perhaps it can be turned off and on and is actually a means to summon Chinese Batman

Cymek said:

Perhaps it can be turned off and on and is actually a means to summon Chinese Batman

And his sidekick…no, i won’t say it. The disapproval would be unbearable.

captain_spalding said:

Cymek said:

Perhaps it can be turned off and on and is actually a means to summon Chinese Batman

And his sidekick…no, i won’t say it. The disapproval would be unbearable.

You can’t go lobbin racist names around

party_pants said:

captain_spalding said:

Cymek said:

Perhaps it can be turned off and on and is actually a means to summon Chinese Batman

And his sidekick…no, i won’t say it. The disapproval would be unbearable.

You can’t go lobbin racist names around

The very idea!

Anyway, the Chengdu street-lighting-boost story is clearly a bullshit cover for something.

There’s a 3/4 moon at the moment. Go outside tonight, look at the ambient light level, and ask yourself ‘would a 20% increase in this light level really be of any help in reducing street-lighting costs? Especially in a Chinese city with an air pollution level as yet unseen in ths country’.

captain_spalding said:

Anyway, the Chengdu street-lighting-boost story is clearly a bullshit cover for something.

There’s a 3/4 moon at the moment. Go outside tonight, look at the ambient light level, and ask yourself ‘would a 20% increase in this light level really be of any help in reducing street-lighting costs? Especially in a Chinese city with an air pollution level as yet unseen in ths country’.

Could it be a proof of concept for a space based mirror used to focus sunlight on a small area as a weapon or means to significantly heat up the ground for some purpose.

Cymek said:

captain_spalding said:

Anyway, the Chengdu street-lighting-boost story is clearly a bullshit cover for something.

There’s a 3/4 moon at the moment. Go outside tonight, look at the ambient light level, and ask yourself ‘would a 20% increase in this light level really be of any help in reducing street-lighting costs? Especially in a Chinese city with an air pollution level as yet unseen in ths country’.

Could it be a proof of concept for a space based mirror used to focus sunlight on a small area as a weapon or means to significantly heat up the ground for some purpose.

Who knows? Jolly inscrutable, these Orientals.

Cymek said:

captain_spalding said:

Anyway, the Chengdu street-lighting-boost story is clearly a bullshit cover for something.

There’s a 3/4 moon at the moment. Go outside tonight, look at the ambient light level, and ask yourself ‘would a 20% increase in this light level really be of any help in reducing street-lighting costs? Especially in a Chinese city with an air pollution level as yet unseen in ths country’.

Could it be a proof of concept for a space based mirror used to focus sunlight on a small area as a weapon or means to significantly heat up the ground for some purpose.

Following on from DV’s calculations, no. The light would be very faint, like 1,000 of the brightness of a full moon, or less.

What diameter will be the mirror for the artificial moon ?

It’s only a paper moon
Sailing over a cardboard sea

Peak Warming Man said:

It’s only a paper moon
Sailing over a cardboard Chinese sea

https://wordpress.futurism.com/artificial-moon-impossible-says-expert/

Divine Angel said:

https://wordpress.futurism.com/artificial-moon-impossible-says-expert/

Feasiblity is just one aspect.

Don’t get us started on the stupidity of it.