Why haven they attempted a manned mission to mars yet?
Radiation is one of the biggest dangers to long-distance space travelers. Intense bursts from solar flares can kill quickly. But even normal background radiation levels in interplanetary space are high enough to pose dangers, including an increased risk of cancer. While adequate shielding can easily be made with existing technology—a few feet of concrete would work admirably—such materials are too heavy to launch into space. This thorny safety issue can’t be solved the same way on a Mars mission as it was on the International Space Station or the Apollo expeditions to the moon. The Apollo trips, were “little hops,” so there wasn’t time for background exposures to reach dangerous levels. And in the space station, astronauts are close enough to Earth for its magnetic field to protect them from the worst types of radiation. On occasions when short-lived solar flares overpower that protection, the astronauts can huddle in a cramped radiation shelter that doesn’t add vastly to the station’s
