Google is experimenting with balloons that beam the Internet from the sky.

WHAT? The helium-filled balloons are made from a thin polyethylene film and are 15 meters (49 feet) in diameter when fully inflated.

WHERE? They float in the stratosphere about 20 kilometers (12 miles) above the Earth.

HOW? The balloons would sail on the stratosphere's winds in a continuous circuit around the globe. The balloons come equipped with flight computers, and Google would control the balloons' altitude from the ground, keeping them moving along a desired channel by using different winds at different heights.

A BREAKTHROUGH? Google says past attempts to control balloons have involved tethering them or using expensive motors to keep them in place. They say simply sailing with the winds was one of the company's breakthrough ideas.

THE ADVANTAGE? Google says the balloons have the potential to provide Internet access far more cheaply, quickly and widely than traditional underground fiber cables. One downside is that computer users on the ground would need to install a receiver to get the signal.

THE REACH? The transmitter on each balloon would beam down the Internet to an area about 1,250 square kilometers (780 square miles) - twice the size of New York City.

THE CHALLENGE? Managing the flight of just one balloon in our complex and ever-changing atmosphere is a huge challenge. Trying to harmonize an entire fleet of thousands of them will be mind-boggling.