In the 1990s solar flares were a known problem we've yet to solve. Without the earth's magnetic field or eleven feet of concrete, a CME bakes astronauts crispy golden brown.

With the moon shots, we just timed them with solar minimum and hoped to get lucky. But instead of a couple of weeks, a mars shot is nine months in space. So we're going to need some new materials with which to make our crew compartments CME proof.

And this is one of hundreds of problems we need to fix before we can send people to mars. It's going to be a while.