No, they really can’t. Or won’t. But what’s the difference? From National Geographic:
Future astronauts could hitchhike their way to Mars—without the need for aVogon Constructor Fleet. According to a new paper, space explorers could reach the red planet by riding along inside asteroids.
Landing a ship on a space rock would solve a key issue facing Mars travelers: how to shield astronauts from galactic cosmic rays, high-energy particles traveling at near light speed that come from outside the solar system. (Related:”Black Holes Belch Universe’s Most Energetic Particles.”)
Cosmic rays can damage DNA, increasing the risks of cancer and cataracts for space travelers. Current research suggests that the amount of radiation that would bombard an astronaut during a thousand-day, round-trip Mars mission increases his or her risk of cancer by 1 to 19 percent.
The best way to avoid cosmic radiation during space travel is to hide in an asteroid? No matter how technologically challenging this would be, it seems like a step backwards to me.