A robot powered by a ground-based laser beam climbed a long cable dangling from a helicopter on Wednesday to qualify for prize money in a $2 million competition to test the potential reality of the science fiction concept of space elevators.

The highly technical contest brought teams from Missouri, Alaska and Seattle to Rogers Dry Lake in the Mojave Desert, most familiar to the public as a space shuttle landing site.

The contest requires their machines to climb 2,953 feet up a cable slung beneath a helicopter hovering nearly a mile high.

LaserMotive's vehicle zipped up to the top in just over four minutes and immediately repeated the feat, qualifying for at least a $900,000 second-place prize.

The device, a square of photo voltaic panels about 2 feet by 2 feet and topped by a motor structure and thin triangle frame, had failed to respond to the laser three times before it was lowered, inspected and then hoisted back up by the helicopter for the successful tries.

Earlier out on the lakebed, team member Nick Burrows had pointed out how it grips the cable with modified skateboard wheels and the laser is aimed with an X Box game controller.

It had never climbed higher than 80 feet previously, he said.

The day's competition began late after hours of testing the cable system, refueling the helicopter and waits for specific time windows in which the lasers can be fired without harming satellites passing overhead.

The Kansas City Space Pirates went first with a machine that initially balked but eventually began climbing. Its speed was too slow to qualify for any prizes but it got within about 160 feet of the top before the laser had to be shut down for satellite protection.

Ben Shelef, CEO of the contest-sponsoring Spaceward Foundation, said the Pirates had a minor laser tracking problem but the real problem appeared to be in the mechanical system.

As the afternoon grew late, the University of Saskatchewan's Space Design Team had to put off its attempts until Thursday. All three teams had further chances to qualify through Friday.

The competition was five years in the making, Shelef said.

"A lot of hurdles to cross," he said. "Now that it's happening I'm actually happy already. It doesn't matter what the outcome is."

Funded by a NASA program to explore bold technology, the contest is intended to encourage development of a theory that originated in the 1960s and was popularized by Arthur C. Clarke's 1979 novel "The Fountains of Paradise."

Space elevators are envisioned as a way to reach space without the risk and expense of rockets.

Instead, electrically powered vehicles would run up and down a cable anchored to a ground structure and extending thousands of miles up to a mass in geosynchronous orbit — the kind of orbit communications satellites are placed in to stay over a fixed spot on the Earth.

Electricity would be supplied through a concept known as "power beaming," ground-based lasers pointing up to photo voltaic cells on the bottom of the climbing vehicle — something like an upside-down solar power system.

The space elevator competition has not produced a winner in its previous three years, but has become increasingly difficult.

The vehicles must climb at an average speed of 16.4 feet per second, or about 11 miles per hour, to qualify for the top prize. A lesser prize is available for vehicles that climb at 2 meters per second.

The rules allow one team to collect all $2 million or for sums to be shared among all three teams depending on their achievements.

While the concept of an elevator to space may seem too fanciful, Andrew Williams, 26, a mechanical engineer on the Saskatchewan team, said he has no doubts it will come about.

"Once we put our minds to something it's just a matter of time for us to achieve it," he said.