Last week it was an electric airplane reaching 155 knots. This week, we're reporting on Solar Impulse, a Swiss-based project aimed at launching an airplane around the world using only the power of the sun. According to team leaders, the aircraft will need to "[push] back the current technological limits in all fields." But the team believes the single-seat aircraft will be able to circumnavigate the Earth without issuing so much as an ounce of carbon or other pollutants. The Solar Impulse weighs 3,300 pounds at takeoff and incorporates 12,000 photovoltaic cells. Its four electric motors, driven by lithium polymer batteries, will spin props at 200 to 400 rpm and cruise at approximately 60 knots. Takeoff is said to be at about 19 knots. The Solar Impulse was unveiled last week. No word on a timetable for the planned global flight.