# Sun orbiting optics

#### aeroegnr

I was curiuous about the materials that would be used to make a giant sun-orbiting reflector, and approximately how close they could be to the sun's center without being destroyed by heat/flares.

Why?

Just wanted to know the feasability of using wasted solar energy (meaning energy that normally just shoots into space in no particular direction) to heat up a suitable planet, like mars.

What kind of devices would be used, and how big would they be? I calculated a reflective sheet orbiting at the distance of mercury's orbit would require a functional radius of around 9*10^5m, which is quite a bit of material, to double the radiation reaching mars. This obviously isn't within the scope of todays technology to launch and deploy.

Is there something out there that would achieve the same effect with much less material, like maybe a closely orbiting lens?

What kind of climate change would doubling the radiation reaching mars achieve?

Yeah I know its a complex question.

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#### chroot

Staff Emeritus
Gold Member
Well, there are only two ways to increase the flux received from the Sun:

1) increase the area of the object
2) get it closer to the Sun

All that you're really doing when you do either of these things is making the object subtend a larger solid angle as seen from the Sun. The Sun's energy is radiated uniformly over its entire 4 pi steradian solid angle, and you can capture more energy if you subtend a larger solid angle. There is no other way.

- Warren

#### Ambitwistor

You might actually want to read Kim Stanley Robinson's Mars trilogy of science fiction novels. He discusses the terraforming of Mars in great detail, including an orbiting mirror/lens combination to increase insolation. Knowing him, he probably worked out some of the math himself. (He postulated better-than-modern materials engineering, though.)

There are probably published studies on this idea somewhere, but I don't know where.

#### wimms

Radio antennas and reflectors can be made from wire grid. Wavelength defines needed grid spacing. For Sun, you'd be interested in infrared I guess, like 900nm. Dunno how to calculate quickly, but I guess needed spacing is close to 900nm. Nanotubes came to mind immediately . Imagined kind of net cloth with parabolic shape as mirror, unfolding at needed position and kept at right angles to direct the beam where needed. Some good bunch of those near sun orbit. Lightweight stuff.
Infact, such bunch of mirrors could be quite a strong weapon, possibly usable to deflect or destroy comets or asteroids on earth collision course, and as energy source for light sail propulsion vehicles.
Search for "Solar sails" or sunlight propulsion.

#### aeroegnr

I guess next week in physics is when I get to optics...

I suppose if a parabolic reflector were used, propulsion by light could get us fairly quickly through the solar system.

Actually, if we had a grid of those materials between the sun and us, we could also control the climate of our planet, and any other planet.

Can a nanotube strucure survive that kind of radiation from the sun though? Wouldn't the energy melt the strucures we put there unless it had a way to disappate incoming energy?

....I just thought initially how much energy the sun sends to nowhere. Maybe if we had some kind of permanent orbiting structure (not a dyson sphere, something much smaller) that collected energy from the sun specifically to make antimatter for fuel. That would really speed up our exploration of our solar system/universe. We could send the probe out there with antimatter containers and ferries to return the antimatter to where its needed. Eventually, we could have a solar highway of antimatter shipments coming in. That's a lot of free power in the most compact form possible.

I know that antimatter can be made in particle accelerators, but I don't think that we produce the amount of power we could get from a sun-orbiting station. Is there another way to make antimatter with a smaller structure than current accelerators (something small enough to be put into space), given a whole bunch of energy to run the process?

I just like the idea of sun brewed antimatter, just waiting there for us to use it when we need it.

B

#### birdus

Another problem, I think, is the large quantity of small bodies orbiting the sun. Debris from comets and such eventualy come close to the sun. Whatever, device you would put there would frequently take high velocity hits.

#### russ_watters

Mentor
Originally posted by birdus
Another problem, I think, is the large quantity of small bodies orbiting the sun. Debris from comets and such eventualy come close to the sun. Whatever, device you would put there would frequently take high velocity hits.
There really isn't much bigger than dust particles and such a mirror could certainly handle a bunch of micrometeroite pinholes. Plus, remember most matter in the solar system orbits the sun in the same direction. I don't think its a very big concern.

This is something I have been curious about too. A few dozen reflectors of a few square miles of mylar would be a nice help to the power grid. For simplicity (you do have to AIM them), it would probably be best to put them in geostationary orbit.

#### enigma

Staff Emeritus
Gold Member
Dust going at tens of km per sec does quite a bit of damage, and you get impacts constantly regardless of your orbit.

#### enigma

Staff Emeritus
Gold Member
http://setas-www.larc.nasa.gov/LDEF/MET_DEB/md_impact.html [Broken]

Long Duration Exposure Facility

5.75 years in LEO. 4000 visible impact craters. Over 15,000 additional smaller impacts. That experiment was turned to swiss cheese.

http://setas-www.larc.nasa.gov/LDEF/MET_DEB/photos/glass1.gif [Broken] is what will most likely happen to any mirror or lens placed in space for any length of time.

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#### Integral

Staff Emeritus
Gold Member
What energy are you collecting? How do you store it? How do you transport it to earth? These are all questions that would need very specific answers before you could design your collector.

I have imagined panaling the moon with photovoltaic cells, the collected power could, with some difficuties be beamed back to earth. This project would/could change the face of the moon as we see it. Since we would be controlling the reflectivity of the moon. I wonder how much Coke would pay to turn the full moon into the Coke symbol?

#### russ_watters

Mentor
Originally posted by enigma
Dust going at tens of km per sec does quite a bit of damage, and you get impacts constantly regardless of your orbit.
Only if it hits something it can damage. It won't do anything more to a mylar sheet than poke a hole in it.

#### wimms

Also, I wonder if such Sun orbiting structure is easily usable as interferometer/telescope?

"Sun orbiting optics"

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