Loon is an experimental project carried out in the framework of Google's X projects to create a network of balloons traveling on the troposphere/stratosphere. The project lead by Mike Cassidy, was born in early 2012 in the restricted access facility that Google have near Mountain View, California.

In the future the fully developed system could offer access to internet above rural and remote areas and also could help fill coverage gaps or help to connect people in zones affected by disasters.

The balloons used in the project are of the superpressure type, made of thin polyethylene plastic and measuring fifteen meters wide by twelve meters tall when fully inflated. They were designed and fabricated by Raven Industries, from Sioux Falls, United States, one of the leading firms in the fabrication of high altitude balloons for scientific and military purposes.

Beneath each balloon is attached a small box containing circuit boards that control the system, radio antennas to communicate with other balloons and with Internet antennas on the ground, and batteries wich are powered by an array of flexible solar panels that sits between the envelope and the box. In full sun, these panels produce 100 Watts of power - enough to keep the unit running while also charging a battery for use at night. A parachute attached to the top of the balloon envelope allows for a controlled descent and landing whenever a balloon is taken out of service.

Project Loon uses software algorithms to determine where its balloons need to go: taking advantage of the different directions of winds at different altitudes they are able to steer the balloons by rising or descending them to an altitude with winds moving in the desired direction. By moving with the wind, the balloons can be arranged to form one large communications network. Each one can provide connectivity to a ground area about 40 km in diameter at speeds comparable to 3G. For balloon-to-balloon and balloon-to-ground communications, the balloons use antennas equipped with specialized radio frequency technology.

Project Loon currently uses ISM bands (specifically 2.4 and 5.8 GHz bands) that are available for anyone to use using a special Internet antenna attached to their building. The signal bounces from balloon to balloon, then to the global Internet back on Earth.

The project started under strict secrecy in March 2013 with test balloons launched from Moffet Field, California and moved to public view in June 2013 with a pilot experience carried out in Christchurch and Canterbury, in the south island of New Zealand where a small group of local users is testing the technology after the launching of a mini constellation of 30 balloons.

The idea is no new: in 2008 a firm called Space Data made some test of a similar balloon-based concept over some rural zones of the United States, however Loon project appears to had achieved a bigger advance than similar initiatives in the past.

Future perspectives for Loon project are to scale-up the tests extending the coverage area to several countries located along the 40th parallel as Australia, Argentina, Chile, Paraguay and Uruguay.

Curiously, Christchurch was during late 60's and early 70's one of the most actives spots for launches of small superpressure balloons. In those years the National Center for Atmospheric Research developed the so called GHOST program aimed to trace the circulation patterns of winds in the southern hemisphere.