LOS ANGELES (AP) _ Wanted by the Pentagon: A muscular, outdoorsy specimen. Must be intelligent and, above all, self-driven.
When 20 hulking robotic vehicles face off next month in a rugged race across the Nevada desert, the winning machine (if any crosses the finish line) will blend the latest technological bling and the most smarts.
The military sponsors the race to speed the development of unmanned vehicles for combat. The project had an inauspicious start: Last year's inaugural contest ended soon after it began when the robots careened off course or abruptly stalled. One even got tangled in barbed wire.
Fast forward 18 months, and double the prize to $2 million.
Newcomers have joined a handful of last year's teams to form a motley mix of garage tinkerers, academia and corporations. All hope that their machines _ fitted with the latest sensors, cameras and computers _ have aged a generation since last year.
Teams have beefed up their vehicles' artificial intelligence through improved computer algorithms that will help them avoid pitfalls such as ditches and boulders strewn across the roughly 150-mile-long course. To get there, the robots must compete in a semifinal showdown that starts Wednesday.
Entrants include several converted SUVs, souped-up passenger sedans, a modified all-terrain vehicle, a behemoth military truck and even a motorcycle.
This year's race shows signs of being extremely competitive. Some vehicles have logged hundreds of self-guided miles in the Southwest desert during summer practice runs. Several even tested on last year's course, which spanned the Mojave Desert between Barstow, Calif., and Primm, Nev.
The ramped-up preparation reflects the higher stakes for the so-called Grand Challenge. While sweetening the purse, organizers promise that the course, which this year loops from and to a casino town on the Nevada-California border called Primm, will be tougher and meaner.
Vehicles will have to drive on dirt and gravel, maneuver mountain switchbacks, squeeze through choke points and avoid man-made and natural obstacles.
The sponsor of the Grand Challenge is the research arm of the Pentagon known as the Defense Advanced Research Projects Agency, or DARPA, whose best-known success story is the Internet. The Pentagon wants one-third of the military's ground vehicles to be unmanned by 2015.
DARPA Director Anthony Tether hopes that a robot will be able to traverse the course in under 10 hours and snatch this year's prize.
``It's going to be a long day out in the desert,'' Tether said.
On Wednesday, 40 teams and three alternates compete for a spot in the Oct. 8 race during the semifinals at the California Speedway in Fontana.
The vehicles must negotiate a 2-mile stretch of the track using on-board computers, global positioning satellites and various lasers and radar. The top 20 performers will advance to the final starting line.
Last year's semifinals were disappointing. Only seven entrants completed a flat, 1.4-mile obstacle course. Even so, organizers let 15 vehicles compete in the finals.
One of the favorites again this year is the Red Team from Carnegie Mellon University in Pittsburgh, led by robotics professor William ``Red'' Whittaker.
During last year's finals, Carnegie Mellon's converted Humvee, nicknamed Sandstorm, traveled the farthest _ all of 7 1/2 miles _ before breaking down. This year, the school entered two robots _ an improved Sandstorm and a converted Hummer named H1ghlander.
The Carnegie Mellon team already has subjected both vehicles to extreme off-roading and hairpin driving in the desert outside Carson City, Nev.
``I'm so hungry for race day,'' Whittaker said.
Among the newcomers: the Stanford Racing Team, whose modified Volkswagen Touareg, Stanley, recently drove 200 miles without interruption or human help in the Arizona desert.
Team leader Sebastian Thrun, a computer science professor at Stanford University, declined to reveal how long the journey took.
``That's our best kept secret,'' he said.
The autonomous robotic vehicles use ``drive-by-wire'' technology, in which on-board computers control steering, braking and other movement. As a result, many of the mechanical linkages to the engine are absent.
The vehicles also have sensors that pinpoint their location and determine whether obstacles lie ahead. The sensors feed data to computers that, with the help of a three-dimensional camera, let vehicles distinguish a boulder from a tumbleweed and calculate whether a chasm is too deep to cross.
Participants generally agree that the sturdier the vehicle, the better it can handle curves and maneuver rocky terrain. But the secret weapon, many say, is each robot's computer brain. It must have all the right algorithms and programming to gather information, plot its path and change course to avoid danger.
DARPA's Tether said this year's selection process was rigorous. Nearly 200 participants from 37 states and three foreign countries applied _ double that of last year.
Unlike last year, teams had to send in a video showcasing their robot's abilities and a crew of judges then fanned across the United States and Canada to check them in action.
The course will not be revealed until two hours before the start time, when DARPA will give contestants a CD-ROM with GPS coordinates that chart the exact route.
If a winner crosses the finish line, Tether said, DARPA will probably not sponsor the same race next year. That would be ``anticlimactic,'' he said.
But if no one wins this year, the stakes will be raised again, to $4 million.