It is an unmanned solar powered aircraft with panels covering the top of it's 74.1 metre series of wings which supply energy to 14 propellers on electric motors.  By 2003 the excess solar energy will be used in a device called an electrolyzer which takes water carried on board the plane and splits it into it's base elements, oxygen and hydrogen.  At night these elements are combined in a fuel cell which powers the motors and produces water so the cycle goes on and Helios can fly by day and night.

Piloted by two controllers using computers on the ground, the plane has cost over $30 million US, approximately $60 million Aus, and is the result of research and development between NASA (the National Aeronautics and Space Administration) and a company in Monrovia, California called AeroVironment Inc. which has been involved in creating solar powered planes for 30 years.

It had it's first trials in 1999 at Edwards Air force Base and on the 14th of July 2001 had a more public showing in Hawaii.  Helios is mainly constructed out of carbon fibre, Kevlar and styrofoam and weighs less than a fully fuelled, single engine Cessna 172.

The future for this aeroplane is most likely as an alternative, cheaper type of satellite or in the military due to it's silence and ability to avoid radar detection.