Dangerous levels of radiation in space could bar astronauts from a mission to Mars and limit prolonged activity on the moon, experts now caution.

However, more research could reveal ways to handle the risks that radiation poses to space missions.

The magnetic field of Earth protects humanity from radiation in space that can damage or kill cells. Once beyond this shield, people become far more vulnerable.

A return to the moon or a mission to Mars that NASA and other space agencies are planning would place astronauts at continued risk from cosmic rays or dangerous bursts of solar radiation.

Several reports in the past have outlined the potential risks.

When it comes to shielding astronauts from radiation, spacecraft designers and mission planners have to consider trading off a safe amount of protective material

Crafts that are too heavy simply can't carry enough fuel to make flight practical