Shortly after midnight in early May, a strange aircraft approached Phoenix’s Sky Harbor International Airport. It had the wingspan of a jumbo jet but flew at only about 40 miles per hour; 16 bright, bluish-white lights shone along the leading edge of its spindly wings. Concerned Phoenicians called the police to report an alien landing.
Sky Harbor’s air traffic control explained to Phoenix police that the ostensible UFO was really a solar-powered airplane: the Solar Impulse, an experimental aircraft completing the first, 19-hour leg of a flight across the United States. Then the police asked how it could fly at night if it’s solar-powered. (Batteries.)
The Solar Impulse is scheduled to take off on Wednesday for its next leg, from Phoenix to Dallas. The 830-mile trip would be the longest ever for a piloted solar aircraft.
The part of the UFO story that most pleases Dr. Bernard Piccard, the Swiss explorer who flew the Solar Impulse into Phoenix is that so many people noticed the lights, which are made from energy-efficient light-emitting diodes (LEDs). Together, all 16 lights consume just 150 watts, Piccard says.
Minimizing power consumption is a crucial consideration for a plane that carries no fuel and gets all its energy from sunlight. It stores solar energy in specially designed batteries during the day so it can keep its four slowly spinning propellers turning at night.
More gangly than a dragonfly, the Solar Impulse is built for lightness, rather than strength. It can’t withstand heavy turbulence, so the team has to wait for a clear weather report before taking off. After Dallas, the next planned stops are St. Louis, Washington, and New York. When a storm is brewing ahead, the plane can turn back or circle in place until the problem blows off.
Piccard is a psychiatrist and adventurer who is chairman of the Solar Impulse venture. He alternates piloting the Solar Impulse with Andre Borschberg, the project’s chief executive officer, a Swiss engineer and former fighter pilot who will helm the Phoenix-to-Dallas leg. The project’s ultimate goal is to fly the Solar Impulse around the world in 2015.