PARIS (AFP) - Scientists believe they have found a way of protecting astronauts from a dangerous source of space radiation, thus lifting a major doubt clouding the dream to send humans to Mars. Their breakthrough takes forward ideas born in the golden age of science fiction, including a proton shield used in the TV show "Star Trek," says one of the researchers. Space weather is one of the greatest challenges facing Mission Red Planet sketched by the United States and Europe for some three decades from now. Even the shortest round trip " the distance between the two planets varies between 55 million (34 million miles) and more than 400 million kms (250 million miles) " would take at least 18 months. During this time, the crew would be exposed to sub-atomic particles that whizz through space, capable of slicing through DNA like a hot knife through butter and boosting the risk of cancer and other disorders. The peril has been known for nearly half a century but has seemed insoluble because costs and technological difficulty. Some experts have toyed with the idea of shielding the crew with lead or massive tanks of water, but the price of lifting this load into orbit from Earth is mind-spinning. Another idea, born in the 1960s, would be to swathe the spaceship with a replica of Earth's own magnetic field. Our weak two-pole field deflects incoming cosmic rays, protecting life on Earth as well as astronauts in low Earth orbit. According to these calculations, the spacecraft would have to generate a magnetic field hundreds of kilometres (miles) across. But such equipment would be huge and drain the ship's energy supply and its powerful field could well harm the crew. British and Portuguese scientists have taken a fresh look at this old concept and say the magnetic field does not, in fact, have to be huge " just a "bubble" a few hundred metres (yards) across would suffice. "The idea is really like in 'Star Trek', when Scottie turns on a shield to protect the starship Enterprise from proton beams " it's almost identical really," Bob Bingham of the Rutherford Appleton Laboratory near Oxford told AFP. Their study, published on Tuesday in a specialist journal by Britain's Institute of Physics, draws on numerical simulation that is also used by experts in nuclear fusion, in which a hot plasma is kept in place by a powerful magnetic field. This number-crunching technology gives a far more accurate picture of how individual particles behave when they collide with a two-pole magnetic field. As a result, the researchers have been able to devise a smarter, miniaturised model of magnetic protection rather than the blunderbuss-style field generator that was envisaged in the past. Using a plasma lab at the Superior Technical Institute in Lisbon, the team tested a scaled down version of the device " its full details are secret, as patents are being sought " in a simulation of a solar storm of atomic particles. Scaled up for a trip to Mars, the device would weigh around "several hundred kilos" (500-700 pounds) and use only about a kilowatt of energy, or around one half to one third of the typical power consumption of today's communications satellites, said Bingham. The force of the magnetic field would replicate that of Earth's but, to minimise any risk to crew close to its source, could be carried in unmanned spacecraft flying either side of the crewship. Bingham said the "mini magnetosphere" was being pitched both to the European Space Agency (ESA) and NASA. It would scatter almost all particles dispatched in "solar storms" " protons belched out by the Sun, he said. It would not work against a somewhat less dangerous problem, of high-energy cosmic rays that fly across interstellar distances, but the ship could be swathed with material, like a kevlar bulletproof waistcoat, against that threat. "It certainly will be the answer if we go to Mars, because going to Mars will take about 18 months and we need to protect the astronauts against these storms," said Bingham. In 2001, a NASA study found that at least 39 former astronauts suffered cataracts after flying in space, 36 of whom had taken part in missions beyond Earth's orbit. Separately, the agency has tentatively estimated that a trip to Mars and back would give a 40-year-old non-smoking man a 40 percent risk of developing fatal cancer after he returned to Earth, or twice the terrestrial risk.