ilan
10-28-2018, 12:21 PM
Why China’s artificial moon probably won’t work
Nathaniel Scharping, Astronomy | Friday, October 26, 2018
Launching a man-made night light into orbit and keeping it in place might be harder than it seems.
http://www.astronomy.com/-/media/Images/News%20and%20Observing/News/2018/10/MoonNight.jpg?mw=500&mh=400
To step outside on a moonlit night is to see the darkness pushed back. The reflected sunlight from our natural satellite during a nearly full moon is enough to limn the nighttime landscape in silver and allow even human eyes to penetrate the gloom. But we can always do better, right? If one moon is good, surely two is even better.
One Chinese researcher thinks so, at least. Wu Chunfeng, head of the Tian Fu New Area Science Society, wants to use a satellite like an artificial moon, reflecting sunlight back to targeted areas of the Earth at night. The reflector would orbit above a city, providing enough illumination to replace lights on the ground with a steady glow and potentially saving on electricity costs.
Brighten the Night
He imagines a shiny satellite unfurling in space about 300 miles above the ground and orienting itself toward cities on the ground. One would be enough to light up around 5o square miles, he says, according to China Daily, and several working in concert could brighten up to 4,000 square miles. Wu says the first should be ready to launch in 2020, and three more in 2022, though the details of the project remain largely unknown.
The plan might not be all that sound, though, according to satellite experts. Based on the scant details available, in fact, the satellite would probably never work, says Ryan Russell, an associate professor of aerospace engineering at the University of Texas at Austin.
The biggest flaw? A satellite flying low enough to deliver that much light wouldn’t be able to stay in one place.
“Their claim for 1 LEO sat at [300 miles] must be a typo or misinformed spokesperson,” Russell says in an email. “The article I read implied you could hover a satellite over a particular city, which of course is not possible.”
Satellites that stay over a fixed point on the Earth, what’s called a geostationary orbit, sit much further away: about 38,000 miles. At that distance, the reflective surface would need to be massive to deliver enough light for humans to see back to Earth. At a distance of just 300 miles the moon would whip around the Earth at thousands of miles per hour, beaming its light on any one place for only a fraction of a second.
You could keep an artificial moon in place with rocket thrusters, says Iain Boyd, an aerospace engineering professor at the University of Michigan, but that would eat up fuel, adding to the cost and requiring constant refueling.
A constellation of satellites circling the Earth would be necessary to keep the lights on all night, trading off reflective duties to one another as they passed by overhead. And even then, fuel is necessary to counteract the tiny atmospheric drag present even in low orbits above Earth. The International Space Station, for example, orbits at about 250 miles up and must be constantly boosted back to its orbit as it slows down due to drag.
The cost of launching and refueling multiple satellites would likely far outpace the savings on electricity, at least for the time being.
Nathaniel Scharping, Astronomy | Friday, October 26, 2018
Launching a man-made night light into orbit and keeping it in place might be harder than it seems.
http://www.astronomy.com/-/media/Images/News%20and%20Observing/News/2018/10/MoonNight.jpg?mw=500&mh=400
To step outside on a moonlit night is to see the darkness pushed back. The reflected sunlight from our natural satellite during a nearly full moon is enough to limn the nighttime landscape in silver and allow even human eyes to penetrate the gloom. But we can always do better, right? If one moon is good, surely two is even better.
One Chinese researcher thinks so, at least. Wu Chunfeng, head of the Tian Fu New Area Science Society, wants to use a satellite like an artificial moon, reflecting sunlight back to targeted areas of the Earth at night. The reflector would orbit above a city, providing enough illumination to replace lights on the ground with a steady glow and potentially saving on electricity costs.
Brighten the Night
He imagines a shiny satellite unfurling in space about 300 miles above the ground and orienting itself toward cities on the ground. One would be enough to light up around 5o square miles, he says, according to China Daily, and several working in concert could brighten up to 4,000 square miles. Wu says the first should be ready to launch in 2020, and three more in 2022, though the details of the project remain largely unknown.
The plan might not be all that sound, though, according to satellite experts. Based on the scant details available, in fact, the satellite would probably never work, says Ryan Russell, an associate professor of aerospace engineering at the University of Texas at Austin.
The biggest flaw? A satellite flying low enough to deliver that much light wouldn’t be able to stay in one place.
“Their claim for 1 LEO sat at [300 miles] must be a typo or misinformed spokesperson,” Russell says in an email. “The article I read implied you could hover a satellite over a particular city, which of course is not possible.”
Satellites that stay over a fixed point on the Earth, what’s called a geostationary orbit, sit much further away: about 38,000 miles. At that distance, the reflective surface would need to be massive to deliver enough light for humans to see back to Earth. At a distance of just 300 miles the moon would whip around the Earth at thousands of miles per hour, beaming its light on any one place for only a fraction of a second.
You could keep an artificial moon in place with rocket thrusters, says Iain Boyd, an aerospace engineering professor at the University of Michigan, but that would eat up fuel, adding to the cost and requiring constant refueling.
A constellation of satellites circling the Earth would be necessary to keep the lights on all night, trading off reflective duties to one another as they passed by overhead. And even then, fuel is necessary to counteract the tiny atmospheric drag present even in low orbits above Earth. The International Space Station, for example, orbits at about 250 miles up and must be constantly boosted back to its orbit as it slows down due to drag.
The cost of launching and refueling multiple satellites would likely far outpace the savings on electricity, at least for the time being.
