Why Humans Still Can't Go To Mars

Long-distance human spaceflight is, famously, a bust. So far, anyway -- no doubt we'll figure it out someday. But the reason we haven't sent humans on five-year missions seeking out new life and new civilizations isn't because of cost, politics, or lack of warp drive. The real reason is that astronauts would probably be killed by radiation before they met their first gas giant.

They wouldn't be dead dead, of course. They might even make it back in time to die on Earth. Yet the outbound trip alone would be enough to send their risk for cancer shooting way beyond what NASA considers acceptable levels.  

How do we know? Well, before they sent the Mars Curiosity rover to the red planet, scientists strapped on a sensor to measure the amount of radiation bombarding its ship. According to newly released data, for every day the vessel spent traveling to Mars, it recorded 1.8 milliSieverts of space radiation.