40kW ironless motors will propel airships on the edge of space

A Californian company has developed a 40kW-plus ironless core motor to propel unmanned, solar-powered airships designed to hover on the edge of space, 21km above the earth`s surface. The multi-role, high-altitude airships (HAAs) are being developed by Lockheed Martin under a $40m-plus contract from the US Department of Defense.

The prototype 40kW motor (above) - thought to be the largest of its type, with the highest torque-to-weight ratio - has been developed by AeroVironment, a company specialising in innovative technologies for energy-efficient systems and unmanned aerial vehicles. The motor (shown above) is designed to deliver large amounts of torque and to operate at part-load efficiencies of more than 98%.

The 150m-long, 50m-diameter airships - 25 times larger than the familiar Goodyear-type blimps - will stay in position for months at a time, performing duties such as observing the weather, carrying out surveillance, and relaying telecommunications signals. One possible military role could be to track low-flying missiles that might slip beneath earth-based radar systems.

The airships (shown in an artist`s impression above) will be able to carry payloads of up to two tonnes. The four motors will power the 10m-diameter propellers to maintain the airships in the required position. Up to 10kW of power will come from thin-film solar cells mounted on the airship`s surface. Excess power will be stored in on-board batteries. Later versions of the HAA may carry fuel cells.

A prototype of the HAA is due to be tested next year. Around ten of the airships will be needed to provide overlapping coverage of the USA`s coastal regions.