Racing with the sun.

Racing with the sun

On an overcast day last month in Mesa, Ariz., an unusual vehicle, shaped like a flattened bullet, raced four times around a 5-mile circular track. On its fourth go-round, the racing car set a new world speed record for a land vehicle powered solely by direct energy from the sun. Taking 8 minutes, 28.628 seconds to complete the circuit, the GM Sunraycer traveled at an average speed of 35.227 miles per hour. This surpasses the previous record of 24.74 miles per hour set by a different vehicle in 1984. The circular course ensured that any wind or terrain effects would be canceled out.

The GM Sunraycer, designed and built by Detroit-based GM Hughes Electronics, is powered by an array of 7,200 solar cells, covering a total of 90 square feet. On a sunny day, the car can move as fast as 45 miles per hour using solar power alone. Because of cloudy conditions on the day scheduled for the record-breaking attempt, the solar cells produced considerably less than their maximum power output. On the road, the car normally uses a battery to provide extra power for acceleration or climbing hills. Under those conditions, it can reach 60 miles per hour. In the race for the record, the car's battery was disconnected.

The car itself is 19.7 feet long, 6.6 feet wide and 3.3 feet high. Its aerodynamically shaped body is constructed from a lightweight, honeycombed composite material over a welded, aluminum-tube frame. The car, including its electric motor, battery, electronic components and solar panel, weighs merely 360 pounds.

The GM Sunraycer was built to compete in a 1,950-mile race for solar-powered vehicles across central Australia from Darwin through Alice Springs to Adelaide. The race begins on Nov. 1 and will probably last at least six days. It features 25 solar vehicles from seven different nations. All vehicles must meet size constraints and have adequate braking, highway lighting and seat belts. They must also be stable in winds up to 40 miles per hour.

Speed alone won't be enough to win the race, says Bruce McCristal of GM Hughes Electronics. "It's a test of durability and reliability,' he says.' "You need a good vehicle and some good luck.' Parts of the road are narrow, and much of it is roughly paved. The terrain varies from lush tropical forest and barren plateau in northern and central Australia to desert and mountains in south Australia. The GM team has only one car, but the team plans to bring along spare parts for just about any problem that could come up.

Because temperatures can go as high as 120|F in the Australian sun, the GM Sunraycer's canopy is plated with a thin film of gold to protect the driver. The film blocks 90 percent of visible light and 98 percent of the infrared radiation. Because the car is driven only in daylight, enough light gets through to enable the driver to see the road.

"We look at this thing as a really interesting scientific effort,' says McCristal. "Our motivation is to push some technologies along that we think are important to the future, and we're very interested in stimulating high-school and college students to get into technical fields [associated with automotive engineering].' The car demostrates advances in low-speed aerodynamics, high-efficiency batteries, lightweight motors and solar cells and panels.