NASA's solar-powered Helios experimental aircraft lifted off from a U.S. Navy base on the Hawaiian island of Kauai on Monday, reaching a height of 96,500 feet.

The $15 million aircraft failed in its attempt to reach an altitude of 100,000 feet, but it broke a record set by its predecessor, the Pathfinder Plus, for 80,201 feet for solar-powered and propeller-driven aircraft in 1998.

Officials decided to bring down the radio-controlled Helios at 4:08 p.m. Hawaii time (10:08 p.m. EDT), NASA spokesman Alan Brown told the Associated Press, as the craft had reached a "zero climb rate" in thinning air and slanting sunlight.

"It's a real milestone of flight," Brown said. "It's a landmark achievement, and especially to do it with a solar aircraft that is nonpolluting. It is a triumph of technology in this area."

The radio-controlled Helios craft, which cruises at speeds of 19 to 25 mph, can reach 103,000 feet under ideal weather conditions, its designers say. It could even be used to fly above Mars, NASA says.

The flight on Monday was delayed for nearly 40 minutes by clouds that prevented the aircraft's 62,000 solar cells from developing enough electricity for take-off. But pilots operating the craft from the ground took advantage of a brief hole in the clouds to get the craft flying.

The Helios, which has a wingspan of 247 feet, has been designed to reach high altitudes and stay aloft for up to three months. It is intended to function like a "poor man's satellite,'' providing telecommunications and other services at a fraction of the cost of launching a satellite into orbit, said John Hicks, project manager for AeroVironment Inc.

AeroVironment has contracted with NASA to develop the craft under the space agency's cooperative Environmental Research and Sensor Technology program.

Helios had its inaugural check-out flight on July 13, when it soared to 76,000 feet. Prior to that, it had been flown only once, in 1999 at Edwards Air Force Base in California, when it reached heights of just 1,000 feet operating on battery power.

Once it demonstrates it can reach the target altitude, engineers will try to develop a lightweight fuel cell system that will allow the craft to fly at night by storing the excess solar power it generates. Currently, the Helios has batteries that allow it to stay up for just a few hours after sunset.

The solar cells will generate about 40 kilowatts of power -- about the amount used each day by four to six homes -- to drive 14 propellers on the craft, which looks like a single boomerang-shaped translucent wing.

When fuel cells are installed by summer of 2003, the Helios will be able to stay aloft for months at a time, Hicks said. And because the Helios will travel close to the Earth, rather than in space orbit like a satellite, it can be brought down easily for routine maintenance and payload changes.

It also can remain in one spot over the Earth's surface for an extended period of time.

AeroVironment is pursuing commercial applications for the craft, but the government plans to use the Helios for a variety of earth science research programs, such as remote-sensing and imaging of the earth's atmosphere and water to study global warming and ozone depletion, Hicks said.

The craft also can be used to monitor the health of fisheries and forest resources, track natural events like hurricanes, tornadoes and volcanic eruptions and even determine the readiness of agricultural crops for harvest, Hicks said.

The military also may use the Helios for surveillance activities because it is essentially a stealth aircraft that is silent and cannot be detected by radar, he said. At maximum altitude, it can fly at speeds of about 200 miles per hour, he said.