PASADENA, Calif. (AP) _ Two softball-size probes are literally on a collision course toward the Red Planet in search of water and test technology that could revolutionize solar system exploration. ``We're not your average mission _ we're slamming into a planet at 400 mph,'' said Deep Space 2 project manager Sarah Gavit at NASA's Jet Propulsion Laboratory. The hardy devices are cruising along with the Mars Polar Lander, which will begin its controlled descent on Friday some 18 seconds before the probes. Unlike the lander, the probes' 77-mile fall will not be slowed by pricey parachutes or thrusters. They will penetrate the planet like lawn darts. Deep Space 2 is risky _ just ask anyone who has destroyed a laptop computer by dropping it. If successful, though, fleets of microprobes could be sent to study more planetary territory at less cost and risk than current spacecraft. The $29.6 million Deep Space 2 probes are part of NASA's New Millennium program, a series of inexpensive missions testing untried technology for future spacecraft. Ten systems will be tried out during the Mars mission. For four years, Gavit and her team have been throwing models out of airplanes over the Mojave Desert and firing electronics out of air guns in Florida to find designs and materials that might survive the force of smashing into the surface. After about 20 attempts, they finally arrived at a design that should withstand the force of impact, which will be 60,000 times stronger than gravity on Earth. Each probe will be protected from the heat of entry by a gray basketball-size aeroshell that will shatter as it hits the surface Friday. Most of the weight is located at one end of each unit to ensure stability, similar to badminton birdies and lawn darts. Impact will cause a silver, bullet-like penetrator to separate from the center of each probe and plunge up to 2 feet into the ground. A cable will connect it to the orange aboveground unit holding an antenna and batteries. Even with successful tests on Earth, there's no guarantee of survival on Mars. The 8-pound probes might hit rocks and shatter. The antennas could be swallowed up by soft dusty soil. A sudden gust of wind could blow them upside down during flight. ``We've got a pretty robust design, but it's like throwing one of these things out here in the middle of Pasadena and saying it has got to penetrate no matter where it lands,'' Gavit said. ``If it lands in the middle of the freeway, it's not going to penetrate.'' The probes should crash to the surface about a mile from each other and 35 miles from the lander in an area about 500 miles north of the planet's south pole. Deep Space 2 will be declared a success if mission controllers receive any signal from one of the probes. Any science data will be considered a windfall, said Suzanne Smrekar, project scientist for Deep Space 2. During descent and impact, instruments will record acceleration for a study of the density of the atmosphere and the surface. A thermometers will track how quickly each probe cools _ measurements that can be used to search for water. But the main water experiment is the most ambitious: After the penetrator stops, a small drill will collect an eraser-size soil sample that will be heated and tested by a laser for evidence of water vapor. ``The water experiment requires a motor to run, a drill to extend. In all the tests, everything worked out,'' she said. ``We're expecting it work. But it certainly by far requires more things to go properly than any of the other experiments.'' Most of the experiments will be completed within an hour and data returned late Friday. The probes will continue to measure soil temperature for two to three days. Gavit is hopeful everything will work despite the leading-edge technology. If not, there's always her other job _ planning an interstellar mission. ''I'm going from a crazy program to something that's really crazy,'' she said.