Chinese City 'Plans To Launch Artificial Moon To Replace Streetlights' (theguardian.com)

The south-western Chinese city of Chengdu is planning to launch an illumination satellite in 2020 that is "designed to complement the moon at night," though it would be eight times as bright. "The 'dusk-like glow' of the satellite would be able to light an area with a diameter of 10-80km, while the precise illumination range could be controlled within tens of meters -- enabling it to replace streetlights," reports The Guardian. From the report: The vision was shared by Wu Chunfeng, the chairman of the private space contractor Chengdu Aerospace Science and Technology Microelectronics System Research Institute Co (Casc), at a national mass innovation and entrepreneurship event held in Chengdu last week. Wu reportedly said testing had begun on the satellite years ago and the technology had now evolved enough to allow for launch in 2020. It is not clear whether the plan has the backing of the city of Chengdu or the Chinese government, though Casc is the main contractor for the Chinese space program.

The People's Daily was quick to reassure those concerned about the fake moon's impact on night-time wildlife. It cited Kang Weimin, director of the Institute of Optics, School of Aerospace, Harbin Institute of Technology, who "explained that the light of the satellite is similar to a dusk-like glow, so it should not affect animals' routines."

Comments

I Predict...

[careysub]

That this won't see the light of day.

Re:I Predict...

[Anonymous Coward]

But if it does, that old copypasta 'The Moon: A Ridiculous Liberal Myth' will have become somewhat real. Interesting times.

It amazes me that so many allegedly "educated" people have fallen so quickly and so hard for a fraudulent fabrication of such laughable proportions. The very idea that a gigantic ball of rock happens to orbit our planet, showing itself in neat, four-week cycles -- with the same side facing us all the time -- is ludicrous. Furthermore, it is an insult to common sense and a damnable affront to intellectual honesty and integrity. That people actually believe it is evidence that the liberals have wrested the last vestiges of control of our public school system from decent, God-fearing Americans (as if any further evidence was needed! Daddy's Roommate? God Almighty!)

Documentaries such as Enemy of the State have accurately portrayed the elaborate, byzantine network of surveillance satellites that the liberals have sent into space to spy on law-abiding Americans. Equipped with technology developed by Handgun Control, Inc., these satellites have the ability to detect firearms from hundreds of kilometers up. That's right, neighbors .. the next time you're out in the backyard exercising your Second Amendment rights, the liberals will see it! These satellites are sensitive enough to tell the difference between a Colt .45 and a .38 Special! And when they detect you with a firearm, their computers cross-reference the address to figure out your name, and then an enormous database housed at Berkeley is updated with information about you.

Of course, this all works fine during the day, but what about at night? Even the liberals can't control the rotation of the Earth to prevent nightfall from setting in (only Joshua was able to ask for that particular favor!) That's where the "moon" comes in. Powered by nuclear reactors, the "moon" is nothing more than an enormous balloon, emitting trillions of candlepower of gun-revealing light. Piloted by key members of the liberal community, the "moon" is strategically moved across the country, pointing out those who dare to make use of their God-given rights at night!

Yes, I know this probably sounds paranoid and preposterous, but consider this. Despite what the revisionist historians tell you, there is no mention of the "moon" anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched. When President Josef Kennedy, at the State of the Union address, proclaimed "We choose to go to the moon", he may as well have said "We choose to go to the weather balloon." The subsequent faking of a "moon" landing on national TV was the first step in a long history of the erosion of our constitutional rights by leftists in this country. No longer can we hide from our government when the sun goes down..

Re:Wow that sounds super improbable

[WhiplashII]

Nope, GEO wobbles. Satellites up there require station keeping and direction pointing thrusters. (There are some clever ways to limit the directional thrusters, but in GEO there is no way to avoid needing position thrusters and for precise pointing like this you'll need pointing thrusters.)

Can it work? YES!

[BobC]

Let's assume, for the moment, that it is a "good idea". How should it be implemented?

If there is to be only one satellite, then there are only two orbits that can work: GEO and a polar Molniya that has the satellite overhead between dusk and dawn. With more satellites more orbits can work, but let's assume one for now.

Let's figure out how big a mirror is needed. First, it will need to have at least some degree of focus to keep the spot size bounded. That is, a flat plane won't do. Let's compute the total light needed over a 10 km x 80 km ellipse, an area of about 2500 km^2. Given that 1 lux = 1 lumen / m^2, the lumens we need will be lux * area. Let's assume a partial moon (0.1 lux) is the minimum needed. Multiply those numbers, and that's 250,000,000 lumens. Let's say naked sunlight (allowing for atmospheric losses) is roughly 100,000 lux. Area = lumens/lux, yielding a mirror area of 2500 m^2.

And that's for a *perfect* mirror: No losses, with perfect focus. Assuming a circular mirror, that's a minimum diameter of about 60 m. That million-to-one illumination ratio really rocks. So, at a first glance, the optics alone says it's doable, at least near the minimums I've used. VERY doable!

A mirror in a Molniya orbit will have to deal with a rapidly/continuously varying sun angle every night, but there may be rotational tricks to deal with that, *if* we can manage to rapidly change the mirror shape. But it would rapidly complicate things, so let's set the Molniya orbit aside.

A mirror in GEO need only cope with seasonal variations. While we're at it, let's increase the mirror area by a factor of 10, so we'll be sure to have abundant margin to play with; let's say a nice, round 200 m diameter.

We already have communication satellites at GEO that stay aimed with precision for 15 years or more. Of course, they're aiming tiny antennas that are a millionth the size of our mirror, so we still must consider the aiming problem.

Satellites use aiming actuators for the antennas, and thrusters and gyros (torquers) for the satellite body, which combined yield good pointing precision. Our reflector won't have that luxury: The antenna will dwarf any satellite body, and will also have minimal rigidity: It really can't be aimed much at all, and even then not quickly.

To get some rigidity we can spin the mirror, which should also help with its shape, though that may not be needed. The total range of motion needed to track the sun matches the 23.5 degree tilt axis over a year, which is roughly 0.1 degree per day. (Well, OK, the total wobble is 23.5 degrees in each direction, but we only need to split the difference to bounce the sun toward the ground, which is 11.75 degrees, doubled, which gets us back to 23.5 degrees).

Next is the issue of aiming/pointing. Using gas or chemical thrusters alone may be a non-starter, including ion thrusters. But with a spinning disk, we really should be able to use precession. But precess against what?

Given the slow rate of angular motion, I suspect a 100-300 km long gravity tether should be able to provide enough restoring force to make the job manageable. The satellite body will then need only to slightly pivot the mirror relative to the tether, an extremely low-energy operation.

The satellite will still need an ion thruster to stay on-station (very gentle thrust). But even with that, our reflector satellite will be vastly simpler than a communications satellite, and perhaps about the same mass for an equivalent mission duration.

Oh, almost forgot: Let's put a small hole in the center of the mirror so light can reach some solar cells to power the satellite! No reactors or RTGs here.

I think that about does it, as an "educated guess". Total mass isn't really an issue: Some member of the Long March family will be able to loft it.

(Yes, yes, I know I haven't calculated either the atmospheric dispersion or the "f-number" of the optics. But I made the mirror 10x larger so I wouldn't have to!)

Re:Did thwy rewrite the laws of physics

[quenda]

How do you get a mirror that big into geostationary orbit?

Easy. Ask the Russians. They experiomented with this sort of thing in the 1990s.

The mirror deployed successfully, and, when illuminated, produced a 5 km wide bright spot, which traversed Europe from southern France to western Russia at a speed of 8 km/s.[1] The bright spot had a luminosity equivalent to approximately that of a full moon.

https://en.wikipedia.org/wiki/...

Re:Can it work? YES!

[hankwang]

Regarding focusing: even with a perfectly shaped mirror, you can't circumvent the fact that the sun is not a point source. Sun diameter D=1.4e+9 m, sun distance L=1.5e+11 m, geostationary orbit distance R=3.6e+7 m. The spot at the earth surface will have a minimum diameter D R/L=340 km, for ideal optics. The claimed diameter of 10 to 80 km is physically impossible from geostationary orbit. They would need to use low-earth orbit, about 1000 km altitude, which would require multiple satellites to illuminate a single town throughout the night.

By the way, the difference between an ideal focusing mirror and a flat mirror is negligible for illumination purposes. For a 200 m diameter mirror, it would add another 0.2 km to the spot size if it's flat rather than paraboloid.