A robot powered by a ground-based laser beam climbed a long cable dangling from a helicopter to qualify for prize money in a two million dollars (£1.21 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 (nearly 1 kilometre) 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 dollars (£544,788.69) second-place prize.

The device, a square of photo voltaic panels about 2 feet by 2 feet (0.6 metres by 0.6 metres) 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.

LaserMotive's two principals, Jordin Kare and Thomas Nugent, said they were relieved after two years of work. They said their real goal is to develop a business based on the idea of beaming power, not the futuristic idea of accessing space via an elevator climbing a cable.

"We both are pretty sceptical of its near-term prospects," Mr Kare said of an elevator.

The day's competition began late after hours of testing the cable system, refuelling 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 (48 metres) 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.