Can I use a space mirror to melt my driveway ice?


Hothlanta 2010? (Paul Huber/Creative Commons)

The roads of Atlanta will hopefully be thawed soon, but in contemplating an iced-over driveway, the inevitable question arises: Could I use a giant space mirror to concentrate sunlight down to melt my driveway free?

Sadly, both Russian Znamya space mirrors burned up in the atmosphere back in the '90s. While operational, Znamya 2* proved capable of reflecting a 3-mile (5-kilometer) wide patch of light onto the dark side of the Earth. Of course, the patch sped along at a speed of 5 miles (8 kilometers) per hour and only had the intensity of a full moon. For many onlookers, it appeared as a brief flash in the sky. Znamya 2.5 aimed higher but ripped on one of the Mir space station's antennae before it could be tested.

So Znamya was a bit of a flop, but that doesn't mean scientists have given up on the concept. For instance, solar mirrors might help us in our efforts to terraform Mars. The red planet is far too cold, so why not deploy fleets of orbiting reflective balloons to collect sunlight and reflect it down to the chilly surfaces? That's the gist of a study from the University of Arizona's Rigel Woida, who theorizes that such a scheme could raise the Martian temperature in a 150-acre patch to Earth-like levels of warmth.

Other scientists call for the use of space mirrors as a geoengineering or planet hacking measure here on Earth. Only instead of using the mirror to direct sunlight to the surface, we'd use it to divert it away from, say, the Greenland ice sheet. In this way, such a space mirror would help alleviate climate change and prevent rising sea levels.

Or, failing all this, you could always pull a playbook from the scientists of the Third Reich and build a giant weaponized space mirror. Hey, if it can melt cities, then the driveway should be a piece of cake, right? Fortunately for the enemies of Nazi Germany, the scheme was flawed in several ways -- namely in regard to optics. Here's how it was debunked in a 1945 edition of LIFE Magazine (via Neatorama):

"The German plan for building may be proved physically impossible by a simple axiom of optics. This is that light cannot be brought to a sharp, pointed focus with lenses or mirrors unless it comes from a sharp, pointed source. Since the sun appears in the sky as a disk and not as a point, the best any optical system can produce is an image of this disk. At very short focal lengths, the image is small and hot but as the focal length is increased the image becomes progressively bigger and cooler. At the distance the Germans proposed to set up their mirror (3,100 miles) the image of the sun cast on the earth would be about 40 miles in diameter and not hot enough to do any damage."

So there you have it. There's hope for the future, but we're just not going to get deicing space mirrors up and running this week. So grab some salt, gravel and your favorite shovel.

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About the Author: Robert Lamb spent his childhood reading books and staring into the woods — first in Newfoundland, Canada and then in rural Tennessee. There was also a long stretch in which he was terrified of alien abduction. He earned a degree in creative writing. He taught high school and then attended journalism school. He wrote for the smallest of small-town newspapers before finally becoming a full-time science writer and podcaster. He’s currently a senior writer at HowStuffWorks and has co-hosted the science podcast Stuff to Blow Your Mind since its inception in 2010. In his spare time, he enjoys traveling with his wife Bonnie, discussing dinosaurs with his son Bastian and crafting the occasional work of fiction.